Article

A paleolatitude reconstruction of the South Armenian Block (Lesser Caucasus) for the Late Cretaceous: Constraints on the Tethyan realm

February 2015
Tectonophysics 644-645

DOI:10.1016/j.tecto.2015.01.012

Authors:

Maud JM Meijers

University of Graz

Brigitte Smith

Université de Montpellier

Uwe Kirscher

Curtin University

Show all 11 authorsHide

The continental South Armenian Block - part of the Anatolide-Tauride South Armenian microplate - of Gondwana origin rifted from the African margin after the Triassic and collided with the Eurasian margin after the Late Cretaceous. During the Late Cretaceous, two northward dipping subduction zones were simultaneously active in the northern Neo-Tethys between the South Armenian Block in the south and the Eurasian margin in the north: oceanic subduction took place below the continental Eurasian margin and intra-oceanic subduction resulted in ophiolite obduction onto the South Armenian Block in the Late Cretaceous.

Thermal-tectonic history of the İspir-Ulutaş porphyry Cu-Mo deposit, Eastern Pontides: Implications for regional tectonics and exploration of porphyry systems

Article

Full-text available

Mar 2025
ORE GEOL REV

Nilay Gülyüz

This study employs multiple low-temperature thermochronology techniques—Apatite Fission Track (AFT), Apatite (U-Th)/He (AHe), and Zircon (U-Th)/He (ZHe)—to reveal the cooling, exhumation, and preservation history of the İspir-Ulutaş porphyry Cu-Mo deposit, the oldest known porphyry deposit in the Eastern Pontides (∼131 Ma), and to investigate the relative scarcity of the porphyry systems in the Eastern Pontides. The inverse thermal history model reveals a complex multi-stage cooling/exhumation history of the İspir-Ulutaş deposit. The ZHe data and thermal model indicate that the deposit was emplaced at a paleodepth of over 6 km at ∼ 131 Ma. The deposit experienced two major exhumation stages. The first, occurring during the Middle Eocene (∼43–38 Ma), was triggered by anomalous regional compressional forces likely due to the subduction of a mid-ocean ridge along the Bitlis-Zagros suture zone. During this phase, the porphyry system was exhumed to near-surface levels, but only its uppermost parts were eroded. Shortly after, post-collisional volcanic and sedimentary sequences buried the deposit, temporarily protecting it from further erosion. The second major exhumation phase, recorded by AHe data, began around 18 Ma and continues to the present, resulting in approximately 2.5 km of erosion. This phase aligns with the timing of the Arabia-Eurasia collision, which caused gradual uplift and exhumation across the region. In summary, the deep emplacement of the İspir-Ulutaş deposit (>5 km), combined with the post-mineralization burial by Eocene sequences, extended slow exhumation, and drier/continental climatic conditions, played key roles in the preservation of the porphyry system. Lastly, the study proposes that areas in the southern Eastern Pontides, particularly those covered by Eocene sequences, may offer promising exploration targets for new porphyry deposits.

Total Shortening Estimates Across the Western Greater Caucasus Mountains from Balanced Cross Sections and Area Balancing

Article

Jul 2023

The Greater Caucasus orogen forms the northern edge of the Arabia-Eurasia collision zone. Although the orogen has long been assumed to exhibit dominantly thick-skinned style deformation via reactivation of high-angle extensional faults, recent work suggests the range may have accommodated several hundred kilometers or more of shortening since its ~30 Ma initiation, and this shortening may be accommodated via thin-skinned, imbricate fan-style deformation associated with underthrusting and/or subduction. However, robust shortening estimates based upon surface geologic observations are lacking. Here we present line-length and area balanced cross sections along two transects across the western Greater Caucasus that provide minimum shortening estimates of 130-200 km. These cross sections demonstrate that a thin-skinned structural style provides a viable explanation for the structure of the Greater Caucasus, and highlight major structures that may accommodate additional, but unconstrained, shortening.

The South Armenian Block: Gondwanan origin and Tethyan evolution in space and time

Article

Full-text available

Apr 2023
GONDWANA RES

The geodynamic evolution of the South Armenian Block (SAB) within the Tethyan realm during the Palaeozoic to present-day is poorly constrained. Much of the SAB is covered by Cenozoic sediments so that the relationships between the SAB and the neighbouring terranes of Central Iran, the Pontides and Taurides are unclear. Here we present new geochronological, palaeomagnetic, and geochemical constraints to shed light on the Gondwanan and Cimmerian provenance of the SAB, timing of its rifting, and geodynamic evolution since the Permian. We report new 40Ar/39Ar and zircon U-Pb ages and compositional data on magmatic sills and dykes in the Late Devonian sedimentary cover, as well as metamorphic rocks that constitute part of the SAB basement. Zircon age distributions, ranging from ∼3.6 Ga to 100 Ma, firmly establish a Gondwanan origin for the SAB. Trondhjemite intrusions into the basement at ∼263 Ma are consistent with a SW-dipping active continental margin. Mafic intraplate intrusions at ∼246 Ma (OIB) and ∼234 Ma (P-MORB) in the sedimentary cover likely represent the incipient stages of breakup of the NE Gondwanan margin and opening of the Neotethys. Andesitic dykes at ∼117 Ma testify to the melting of subduction-modified lithosphere. In contrast to current interpretations, we show that the SAB should be considered separate from the Taurides, and that the Armenian ophiolite complexes formed chiefly in the Eurasian forearc. Based on the new constraints, we provide a geodynamic reconstruction of the SAB since the Permian, in which it started rifting from Gondwana alongside the Pontides, likely reached the Iranian margin in Early Jurassic times, and was subject to episodes of intraplate (∼189 Ma) and NE-dipping subduction-related (∼117 Ma) magmatism.

Arabia-Eurasia convergence and collision control on Cenozoic juvenile K-rich magmatism in the South Armenian block, Lesser Caucasus

Article

Full-text available

Jan 2022
EARTH-SCI REV

The South Armenian Block (SAB) belongs to the Lesser Caucasus, and it is located where the Central Tethyan belt bends from an EW orientation in Turkey to the NW-oriented Iranian tectonic zones. Magmatism in these belts is the result of convergence, collision and post-collision evolution of the Arabian plate with the Eurasian margin. An exhaustive study including whole-rock major, trace element, and radiogenic isotope (Sr, Nd, Pb) data, and zircon Hf isotopes, and UPb dating has been conducted in three areas of the SAB, including Tejsar, Amulsar and Bargushat. Combined with previous data, this study reconstructs the Cenozoic magmatic and geodynamic evolution of the Turkish-Lesser Caucasian-Iranian magmatic belt, with a particular focus on the SAB. The Cenozoic intrusions in the SAB are dominantly K-rich and characterized by an enrichment in LILE and depletion in Nb, Ta, Ti. They were emplaced in Tejsar and Bargushat between 43.0 and 37.7 Ma, in Amulsar between 35.9 and 32.1 Ma, predating or being contemporaneous with a 37.8 to 28.1 Ma shoshonitic pulse recorded in the southernmost SAB at the Meghri-Ordubad pluton. This K-rich magmatism is characterized by a juvenile mantle dominated composition, evidenced by εHf(i) zircon values higher than 8.1 and εNd(i) whole-rock values higher than 3.1. Modelling of the Nd and Sr isotope data shows that the mid-Eocene to early Oligocene K-rich magmatism of the SAB is the result of low degree partial melting of a metasomatized mantle source (SCLM), mixing with an upwelling asthenospheric mantle. Mid-Eocene-early Oligocene K-rich magmatism in the SAB and NW Iran coincided with a magmatic lull in Turkey at 40–20 Ma. While frontal Arabia-Turkish plate collision totally shut off magmatism, ongoing coeval magmatism in the SAB and NW-Iran is explained by strike-slip fault tectonics during oblique convergence of the Arabian plate along the Iranian and SAB segment. The dominant juvenile mantle signature of the Cenozoic SAB magmatism contrasts with more crustal-enriched sources in the adjacent NW Iranian and eastern Turkish Cenozoic magmatic rocks, revealing a mantle anomaly underneath the SAB. Our study concludes that the compressive to tranpressive tectonic regime in the SAB during Arabia-Eurasia collision resulted in delamination of a metasomatized SCLM, which interacted with a juvenile asthenospheric mantle upwelling underneath the SAB. Low degree partial melting of this mixed mantle reservoir resulted in the formation of the mid-Eocene to Oligocene K-rich magmatic rocks in the SAB.

The East Anatolia–Lesser Caucasus ophiolite: An exceptional case of large-scale obduction, synthesis of data and numerical modelling

Article

Full-text available

Jan 2020

Full text (free access): https://www.sciencedirect.com/science/article/pii/S1674987119300295 We present new, geological, metamorphic, geochemical and geochronological data on the East Anatolian – Lesser Caucasus ophiolites. These data are used in combination with a synthesis of previous data and numerical modelling to unravel the tectonic emplacement of ophiolites in this region. All these data allow the reconstruction of a large obducted ophiolite nappe, thrusted for > 100 km and up to 250 km on the Anatolian-Armenian block. The ophiolite petrology shows three distinct magmatic series, highlighted by new isotopic and trace element data: (1) The main Early Jurassic Tholeiites (ophiolite s.s.) bear LILE-enriched, subduction-modified, MORB chemical composition. Geology and petrology of the Tholeiite series substantiates a slow-spreading oceanic environment in a time spanning from the Late Triassic to the Middle-Late Jurassic. Serpentinites, gabbros and plagiogranites were exhumed by normal faults, and covered by radiolarites, while minor volumes of pillow-lava flows infilled the rift grabens. Tendency towards a subduction-modified geochemical signature suggests emplacement in a marginal basin above a subduction zone. (2) Late Early Cretaceous alkaline lavas conformably emplaced on top of the ophiolite. They have an OIB affinity. These lavas are featured by large pillow lavas interbedded a carbonate matrix. They show evidence for a large-scale OIB plume activity, which occurred prior to ophiolite obduction. (3) Early Late Cretaceous calc-alkaline lavas and dykes. These magmatic rocks are found on top of the obducted nappe, above the post-obduction erosion level. This series shows similar Sr-Nd isotopic features as the Alkaline series, though having a clear supra-subduction affinity. They are thus interpreted to be the remelting product of a mantle previously contaminated by the OIB plume. Correlation of data from the Lesser Caucasus to western Anatolia shows a progression from back-arc to arc and fore-arc, which highlight a dissymmetry in the obducted oceanic lithosphere from East to West. The metamorphic PT-t paths of the obduction sole lithologies define a southward propagation of the ophiolite: (1) PT-t data from the northern Sevan-Akera suture zone (Armenia) highlight the presence and exhumation of eclogites (1.85 ± 0.02 GPa - 590 ± 5 °C) and blueschists below the ophiolite, which are dated at ca. 94 Ma by Ar-Ar on phengite. (2) Neighbouring Amasia (Armenia) garnet amphibolites indicate metamorphic peak conditions of 0.65 ± 0.05 GPa and 600 ± 20 °C with a U-Pb on rutile age of 90.2 ± 5.2 Ma and Ar-Ar on amphibole and phengite ages of 90.8 ± 3.0 Ma and 90.8 ± 1.2 Ma, respectively. These data are consistent with palaeontological dating of sediment deposits directly under (Cenomanian, i.e. ≥ 93.9 Ma) or sealing (Coniacian-Santonian, i.e., ≤ 89.8 Ma), the obduction. (3) At Hınıs (NE Turkey) PT-t conditions on amphibolites (0.66 ± 0.06 GPa and 660 ± 20°C, with a U-Pb titanite age of 80.0 ± 3.2 Ma) agree with previous P-T-t data on granulites, and highlight a rapid exhumation below a top-to-the-North detachment sealed by the Early Maastrichtian unconformity (ca. 70.6 Ma). Amphibolites are cross-cut by monzonites dated by U-Pb on titanite at 78.3 ± 3.7 Ma. We propose that the HT-MP metamorphism was coeval with the monzonites, about 10 Ma after the obduction, and was triggered by the onset of subduction South of the Anatolides and by reactivation or acceleration of the subduction below the Pontides-Eurasian margin. Numerical modelling accounts for the obduction of an “old” ~80 Myr oceanic lithosphere due to a significant heating of oceanic lithosphere through mantle upwelling, which increased the oceanic lithosphere buoyancy. The long-distance transport of a currently thin section of ophiolites (<1 km) onto the Anatolian continental margin is ascribed to a combination of northward mantle extensional thinning of the obducted oceanic lithosphere by the Hınıs detachment at c. 80 Ma, and southward gravitational propagation of the ophiolite nappe onto its foreland basin.

Caucasus collisional history: Review of data from East Anatolia to West Iran

Article

May 2017
GONDWANA RES

Yann Rolland

This article summarizes the geodynamic evolution of the Caucasus mountain belt from the Paleozoic to Present based on a review of works from Eastern Anatolia, Greater and Lesser Caucasus and Western Iran. The geological history of crystalline basements provides evidence for their derivation from Gondwana, for their drift at 450–350 Ma by roll-back of the South-dipping Rheic slab. Accretion to Eurasia of the Pontides-Transcaucasus block (PTB) occurred in the Carboniferous, and later an active continental margin was formed above a North-dipping subduction zone since at least the Early Jurassic. In the Mesozoic, the Neotethys ocean is separated into two domains, to the North and South of an E-W elongated block, the Taurides–Anatolides-South Armenian (ATA) Block. Two major subduction jumps are accounted for closure of the Tethys domain in Mesozoic to Cenozoic times: (i) jump at 90–80 Ma from the Northern to the Southern branch of Tethys after the closure of the northern branch of Neotethys along the Southern Eurasian margin in the Lesser Caucasus following the accretion of the ATA block to the PTB, (ii) jump at c. 40 Ma from the Southern branch of Neotethys to the Greater Caucasus back-arc basin (GCB), following the accretion of the ATA-Bitlis to the Arabian margin. The GCB will close completely during the Late Eocene to Pliocene and will give rise to the Greater Caucasus mountains. The Pliocene times mark an abrupt transition from a phase of convergence accommodated by subduction of marginal basins into a ‘hard’ collisional phase dominated by the reactivation of sutures and leading to a generalized uplift and diffuse deformation in the whole region.

Metallogeny of the Lesser Caucasus: From arc construction to post-collision evolution

Chapter

Oct 2016

This contribution reviews the metallogenic setting of the Lesser Caucasus within the framework of the complex geodynamic evolution of the Central Tethys belt during convergence and collision of Arabia, Eurasia and Gondwana-derived microplates. New rhenium-osmium molybdenite ages are also presented for several major deposits and prospects, allowing us to constrain the metallogenic evolution of the Lesser Caucasus. The host rock lithologies, magmatic associations, deposit styles, ore controls and metal endowment vary greatly along the Lesser Caucasus as a function of the age and tectono-magmatic distribution of the ore districts and deposits. The ore deposits and ore districts can be essentially assigned to two different evolution stages: (1) Mesozoic arc construction and evolution along the Eurasian margin, and (2) Cenozoic magmatism and tectonic evolution following late Cretaceous accretion of Gondwana-derived microplates with the Eurasian margin. The available data suggest that during Jurassic arc construction along the Eurasian margin, i.e. the Somkheto-Karabagh belt and the Kapan zone, the metallogenic evolution was dominated by subaqueous magmatic-hydrothermal systems, VMS-style mineralization in a fore-arc environment or along the margins of a back-arc ocean located between the Eurasin margin and Gondwana-derived terranes. This metallogenic event coincided broadly with a rearrangement of tectonic plates, resulting in steepening of the subducting plate during the middle to late Jurassic transition. Typical porphyry Cu and high-sulfidation epithermal systems were emplaced in the Somkheto-Karabagh belt during the late Jurassic and the early Cretaceous, once the arc reached a more mature stage with a thicker crust, and fertile magmas were generated by magma storage and MASH processes. During the late Cretaceous, low-sulfidation type epithermal deposits and transitional VMS-porphyry-epithermal systems were formed in the northern Lesser Caucasus during compression, uplift and hinterland migration of the magmatic arc, coinciding with flattening of the subduction geometry. Late Cretaceous collision of Gondwana-derived terranes with Eurasia resulted in a rearrangement of subduction zones. Cenozoic magmatism and ore deposits stitched the collision and accretion zones. Eocene porphyry Cu-Mo deposits and associated precious metal epithermal systems were formed during subduction-related magmatism in the southernmost Lesser Caucasus. Subsequently, late Eocene-Oligocene accretion of Arabia with Eurasia and final closure of the southern branch of the Neotethys resulted in the emplacement of Neogene collision to post-collision porphyry Cu-Mo deposits along major translithospheric faults in the southernmost Lesser Caucasus. The Cretaceous and Cenozoic magmatic and metallogenic evolutions of the northern Lesser Caucasus and the Turkish Eastern Pontides are intimately linked to each other. The Cenozoic magmatism and metallogenic setting of the southernmost Lesser Caucasus can also be traced southwards into the Cenozoic Iranian Urumieh-Dokhtar and Alborz belts. However, contrasting tectonic, magmatic and sedimentary records during the Mesozoic are consistent with the absence of any metallogenic connection between the Alborz in Iran and the southernmost Lesser Caucasus.

Metallogeny of the Lesser Caucasus: From Arc Construction to Postcollision Evolution

Chapter

Full-text available

Jan 2016

Nino Popkhadze

From seafloor spreading to obduction: Jurassic–Cretaceous evolution of the northern branch of the Neotethys in the Northeastern Anatolian and Lesser Caucasus regions

Article

Full-text available

Dec 2015

We present arguments for an innovative tectonic set-up just prior to the Northern Neotethys obduction event in the NE Anatolian and Lesser Caucasus area. Along the Northern Neotethyan suture (the Ankara–Erzincan–Amasia–Sevan–Akera suture zone), relicts of the northern branch of the Neotethys oceanic domain outcrop as preserved unmetamorphosed slivers obducted over the northern edge of the South Armenian Block (SAB) and Taurides–Anatolides Platform (TAP) margins. Recent studies have shown that the ophiolitic bodies are formed of similar lithologies of Middle Jurassic age, all bearing mid-ocean ridge basalt chemical compositions enriched in large ion lithophile elements. This extensive database supports a model in which these ophiolites are derived from a single obducted nappe. This model is supported by the metamorphic pressure–temperature–time paths of the sole lithologies under the outcrops of the suture zone ophiolites. Palaeontological dating of sediment deposits directly under or sealing the obduction contact also support this model by temporally linking the emplacement of distant ophiolite outcrops. General emplacement during early Late Cretaceous time has been determined. A south-dipping subduction under the SAB shortly predating obduction has recently been proposed from the metamorphic and magmatic evolution preserved in the SAB crystalline basement, founding a model featuring opposite-direction subduction from at least late Middle Jurassic to Early Cretaceous times. The emplacement of alkaline pillow basalts directly on the oceanic crust is dated as Early to mid-Cretaceous. These dates argue the existence of abnormal mantle heat flows which may be responsible for a decrease in the density of the 80 Ma-old oceanic lithosphere prior to its obduction onto the SAB–TAP. We present a detailed review of recent data to further constrain the structural and geodynamic evolution of this sector and to define the tectonic set-up just prior to the obduction event.

Acritarchs and prasinophytes from the Upper Devonian of Armenia: biostratigraphic and palaeobiogeographic implications

Article

Jan 2025
Palynology

The Frasnian–Famennian (Upper Devonian) siliciclastic sedimentary sequences of the Ertych section, located in south-central Armenia, yielded a relatively diverse and well-preserved marine phytoplankton assemblage consisting of acritarchs and prasinophytes. The former are represented by 19 species belonging to 10 genera; the latter comprise six species (five genera). This constitutes the first report of marine organic-walled phytoplankton from the Upper Devonian successions of the South Armenian Block, which was then part of the northern Gondwanan continental margin. Comparison of the examined assemblage with others documented from elsewhere in Gondwana (e.g. Iran, Africa, South America, Australia), central and east Asia (South China, Tarim, Junggar), Variscan Terranes (Iberia, Armorica), and Laurussia (e.g. North America), establishes a close palaeobiogeographical affinity of the Armenian material with assemblages preserved in the Alborz Mountain Range, Iran. The presence in our material of several index acritarch species in palynomorph zones from the Eastern Alborz Mountains, Iran, signifies correlation with the late Frasnian–early Famennian interval, confirming previous results based on miospores. Furthermore, our observations provide additional data on previously suggested palaeobiogeographical patterns of Late Devonian organic-walled phytoplankton, supporting a closer affinity between floras from central to north-western Gondwana with those of Laurussia compared with those of higher palaeolatitudes (e.g. South America). Indeed, the assemblage from the Ertych section contains species evidently restricted to warm-temperate to arid climate belts.

Paleozoic xenoliths in Eocene plutons: The evidence for the destruction of pre-Jurassic crystalline basement beneath Adjara-Trialeti belt, Lesser Caucasus

Article

Full-text available

Sep 2021
GEOL CARPATH

In Georgia the Paleogene Adjara-Trialeti riftogenic belt (length 350 km, width 50-2 km) is dominantly composed of trachytic and trachytic-andesitic pyroclastic deposits, though plutonic rocks also play an important role in the structure. In this article, we report new data on the (LA-ICP-MS) U-Pb zircon geochronology and petrochemistry of the plutons, their xenoliths and restite from this belt. The results indicate that the magmatism in the basin began in the Early Eocene (~50 Ma) associated with the formation of pyroclastic rocks. The mafic intrusions (~46-44 Ma) led to the assimilation and contamination of sialic crust and formation of monzo-syenite melts emplaced at ~43-42 Ma. The Eocene monzo-syenite plutons contain xenoliths of Paleozoic granites (312±7 to 474±5 Ma) and tholeiitic basalts that contain inherited zircon grains ranging in age from Neo-Proterozoic (747±33 Ma, 632±29 Ma) to Cambrian (515±9 Ma). Paleozoic granite xenoliths show complete mineralogical and age similarity to the Adjara-Trialeti belt adjacent pre-Jurassic massif granites. Inherited zircon grains most likely are captured by magmas during ascent that cuts through the Gondwana-derived old continental crust. Obtained results and regional geological analysis demonstrate that the riftogenic basin of the Adjara-Trialeti belt developed on the pre-Jurassic crystalline basement, from Late Cretaceous to Eocene into a back-arc extensional regime to post-collision geodynamic setting.

At the crossroads of the Lesser Caucasus and the Eastern Pontides: Late Cretaceous to early Eocene magmatic and geodynamic evolution of the Bolnisi district, Georgia

Article

Full-text available

Nov 2020
LITHOS

The Bolnisi district is a distinct tectonic zone of the Lesser Caucasus, which is considered to represent the eastern extremity of the Turkish Eastern Pontides. Late Cretaceous, low-K, calc-alkaline to high-K rhyolite of the Mashavera and Gasandami Suites is the predominant rock type of the district, and is accompanied by subsidiary dacite, and rare high-alumina basalt and trachyandesite of the Tandzia Suite. The Mashavera and Gasandami rhyolite and dacite have yielded U-Pb LA-ICP-MS and TIMS zircon ages between 87.14 ± 0.16 and 81.64 ± 0.94 Ma, which are in line with the Coniacan-Santonian ages of radiolarian fauna of the Mashavera Suite. The felsic rocks of the Mashavera and Gasandami Suites were deposited during a ~6.6 m.y.-long silicic magmatic flare-up event, which together with the Tandzia Suite mafic rocks, documents Late Cretaceous bimodal magmatism in an extensional tectonic setting. Trace element data indicate that high Y-Zr, low- to high-silica rhyolite and dacite, and low Y-Zr high-silica rhyolite have been erupted, respectively, from coeval deep and shallow crustal reservoirs. The rocks of the bimodal magmatic event are overlain by high-K volcanic rocks of the Campanian Shorsholeti Suite, which have been erupted during slab roll-back and steepening, from magmas produced by deep melting of a metasomatised mantle. Eocene postcollisional felsic intrusions crosscut the Late Cretaceous rock. The Coniacian to early Campanian bimodal magmatism, and the subsequent high-K magmatism of the Bolnisi district are contemporaneous and share geochemical characteristics with the Late Cretaceous magmatism of the Eastern Pontides. It documents the existence of a Late Cretaceous regional silicic magmatic province, and subsequent high-K magmatism during slab steepening. This regional magmatic evolution coincided with the opening of the Black Sea and the Adjara-Trialeti basins. This evolution was coeval with the wanning stages of northern Neotethyan subduction, after a ~40 m.y.-long magmatic lull along the southern Eurasian convergent margin. Early Eocene adakite-like magmatism affected both the Bolnisi district and the Eastern Pontides, demonstrating a common postcollisional magmatic evolution.

Continental accretion and incremental deformation in the thermochronologic evolution of the Lesser Caucasus

Article

Apr 2019

Apatite fission-track analysis and thermochronologic statistical modeling of Precambrian–Oligocene plutonic and metamorphic rocks from the Lesser Caucasus resolve two discrete cooling episodes. Cooling occurred during incremental crustal shortening due to obduction and continental accretion along the margins of the northern branch of the Neotethys. (1) The thermochronometric record of a Late Cretaceous (Turonian–Maastrichtian) cooling/exhumation event, coeval to widespread ophiolite obduction, is still present only in a relatively small area of the upper plate of the Amasia-Sevan-Akera (ASA) suture zone, i.e. the suture marking the final closure of the northern Neotethys during the Paleogene. Such area has not been affected by significant later exhumation. (2) Rapid cooling/exhumation occurred in the Early-Middle Miocene in both the lower and upper plates of the ASA suture zone, obscuring previous thermochronologic signatures over most of the study area. Miocene contractional reactivation of the ASA suture zone occurred contemporaneously with the main phase of shortening and exhumation along the Bitlis suture zone marking the closure of the southern branch of the Neotethys and the ensuing Arabia-Eurasia collision. Miocene collisional stress from the Bitlis suture zone was transmitted northward across the Anatolian hinterland, which was left relatively undeformed, and focused along preexisting structural discontinuities such as the eastern Pontides and the ASA suture zone. © 2019 China University of Geosciences (Beijing) and Peking University

Rapid Late Eocene Exhumation of the Sivas Basin (Central Anatolia) Driven by Initial Arabia-Eurasia Collision

Article

Full-text available

Sep 2018

Continental collisions exert a profound influence on the configuration and evolution of orogenic systems. The effects of Arabia-Eurasia collision on the geodynamics of the eastern Mediterranean are difficult to unravel, however, because the timing of initial collision (i.e., intercontinental contact) remains controversial. We present the first detrital and bedrock apatite fission track and (U-Th-Sm)/He thermochronology, and detrital zircon U-Pb constraints from the Sivas Basin and eastern Taurides in central Anatolia (Turkey), which provide a detailed record of Cenozoic orogenesis in the hinterland of the Arabia-Eurasia collision zone. Our results indicate rapid middle Eocene burial followed by shortening, rapid cooling (up to ~25–45 °C/myr), and initiation of the southern Sivas fold-thrust belt (SSFTB) during the late Eocene (~40–34 Ma), consistent with evidence of a coeval basin-wide unconformity. We interpret that rapid late Eocene cooling of the SSFTB reflects exhumation driven by the northward propagation of retroforeland contraction into the Sivas Basin from the middle to late Eocene, and we propose that these events were due to initial soft collision of the thinned Arabian passive margin by ~45 Ma. This timing of the inception of collision is supported by a regional compilation of apatite fission track data that indicates rapid cooling and hinterland exhumation throughout central and eastern Anatolia from ~45 to 30 Ma, which was synchronous with a widespread magmatic lull from ~40 to 20 Ma. The data presented here are compatible with a widely accepted transition to more mature or hard collision at ~20 Ma, after which most collisional strain localized within the Bitlis suture zone.

Sponge-microbial build-ups from the lowermost Triassic Chanakhchi section in southern Armenia: Microfacies and stable carbon isotopes

Article

Nov 2017
PALAEOGEOGR PALAEOCL

The end-Permian mass extinction was the most severe biotic crisis in Earth's history. In its direct aftermath microbial communities colonized some of the space left vacant after the severe decline of skeletal metazoans. The Permian-Triassic boundary microbialites were peculiarly abundant on low-latitude shallow-marine carbonate shelves of central Tethyan continents. Armenia features particularly well preserved and diverse basal Triassic sponge-microbial build-ups (BTSMBs), which were not studied in detail to date. Here, the Chanakhchi section in southern Armenia is described petrographically and by means of stable isotope analyses. The Armenian BTSMBs formed in a distally open marine setting on a pelagic carbonate ramp in the course of two phases of microbial growth during the Induan (Lower Triassic). The BTSMBs are represented by predominantly thrombolitic but also dendrolitic and digitate stromatolite biostromes and mounds that vary in height between 5 cm to 12 m. The digitate stromatolites are associated with calcium carbonate crystal fans (CCFs). Microfacies analyses revealed that the BTSMBs exhibit a number of different growth forms and internal fabrics. The formation of CCFs was apparently not devoid of biological influence and took place above the sediment surface. The abundance of sponges in the BTSMBs reveals that ecologically complex metazoan-microbial reefs have been present already early after the end-Permian mass extinction. However, the formation of biostromes and mounds did not depend on sponges or other metazoans. BTSMBs that formed during the second microbial growth phase revealed similar δ13C-values like the surrounding sediment. In contrast, the δ13Cmicrobialite and δ13Csediment values from the BTSMBs and CCFs of the first growth phase show a difference of up to + 2.3‰, suggesting a significant influence of photoautotrophy during microbially induced carbonate precipitation.

A review of the plate convergence history of the East Anatolia-Transcaucasus region during the Variscan: Insights from the Georgian basement and its connection to the Eastern Pontides

Article

Mar 2016
J GEODYN

This article summarizes the geodynamic evolution of the Variscan to Mesozoic Tethyan subduction history, based on a review of geochronological data from Eastern Anatolia and the Lesser Caucasus, and new isotopic ages for the Georgian crystalline basements. The geological history of the basements of Georgia (Transcaucasus) and NE Turkey (eastern Pontides) appears to be similar and provides evidence for a continuously active continental margin above a north-dipping subduction since at least the Lower Jurassic. New La-ICPMS U-Pb ages from the Georgian basement provide further evidence for the derivation of the Transcaucasus and its western continuation (the eastern Pontides) from Gondwana. A migmatized granodiorite provides preserved magmatic zircon cores with an age of 474 ± 3 Ma, while the age of migmatization is constrained by its 343 ± 2 Ma metamorphic rims. Metamorphism is synchronous with widespread I-type granites that were emplaced at 335 ± 8 Ma in the neighbouring Dzirula massif, and in the eastern Pontides. These U-Pb ages are in close agreement with recently obtained Ar/Ar ages from biotites and muscovites from metamorphic schists and U-Pb ages ranging from 340 to 330 Ma in the Georgian basement. The narrow range of ages suggests that the Variscan LP-HT metamorphic event in the eastern Pontides and Georgia was of short duration and likely related to mantle-derived intrusives. Furthermore, we suggest that (1) rifting of the Pontides-Transcaucasus block (PTB) from Gondwana at 450–350 Ma could have been driven by roll-back of the south-dipping Rheic slab, (2) that the main metamorphic and coeval magmatic events are related to the accretion of the PTB to the Eurasian margin at c. 350 Ma, while the source of magmatism is ascribed to slab detachment of the south-dipping slab at 340 Ma and that (3) three subduction zones may have been contemporaneously active in the Tethyan domain during the Jurassic: (i) the Lesser Caucasus South Armenian Block (SAB) shares a similar Gondwana affinity, but bears younger ages for its MP-MT metamorphic evolution and calc-alkaline magmatism bracketed from 160 to 123 Ma; (ii) north-dipping subduction below the PTB from c. 210 Ma to 150 Ma; (iii) northward intra-oceanic subduction bracketed from 180 to 90 Ma between the SAB and the PTB.

Neotethyan Ankara Melange, central Turkey in its Triassic-Eocene regional tectonic setting including accretionary melanges, magmatic arcs and continental units

Article

Mar 2023

The classic Neotethyan Ankara Melange formed within the Triassic-Eocene İzmir-Ankara-Erzincan ocean (‘N Neotethys’), bordered in central Anatolia by the Kırşehir and Tauride-Anatolide continental units to the south and by the discontinuous Sakarya continent to the northwest. Farther north, the separate Intra-Pontide ocean probably remained partly open until the early Cenozoic. The Neotethyan Ankara Melange developed via phases of intra-oceanic accretion (mainly pre-Aptian), initial continental accretion (i.e. Coniacian (?)), arc magmatism (Upper Cretaceous) and continent-continent collision (Maastrichtian-Early Eocene). Variably dismembered ophiolitic rocks of Early-Middle Jurassic age within the Ankara Melange formed by supra-subduction zone (SSZ) spreading above a generally northward-dipping subduction zone. Volcanic-sedimentary lithologies of Triassic-Cretaceous age represent fragments of oceanic crust including variably sized oceanic seamounts. The oceanic volcanics and sediments accreted from the downgoing plate, whereas the ophiolites represent fragments of the overriding plate. The main driver of accretion in the Ankara area was collision of a large Upper Jurassic-Lower Cretaceous oceanic seamount (probably plume related) and its capping carbonate platform, with Middle-Late Jurassic fore-arc oceanic lithosphere. Intra-oceanic arc and proximal-distal fore-arc basin units developed above the accretionary complex and within remnant Neotethyan ocean to the north during the Upper Cretaceous. After docking with the Sakarya continent, the Ankara Melange was transgressed by continental margin fore-arc and syn-collisional foreland basin sediments (Campanian-Early Eocene). Comparisons with Neotethyan melanges across Anatolia to the Caucasus indicate exceptional development in the type Ankara area.

Assessing inclination flattening in the Holocene: insights from sediment data and global models

Article

Dec 2022

Lacustrine and marine sediments are one of the main sources of information in constructing Holocene global geomagnetic field models. The use of sediment records, however, leads to the question whether the compaction of sediments leads to a systematic biasing of inclination. We evaluate 78 sedimentary records worldwide for inclination flattening using the E/I method; 20 records indicate flattening. The uncorrected and corrected values for inclination are compared to global geomagnetic field models. The results suggest that the uncorrected values agree better with the predictions from global geomagnetic field models based on sediment and archeomagnetic data, but also with a model independent of sediment data. The 20 sites are located in mid-latitudes where inclination anomalies are predicted both in the Holocene and throughout the Brunhes epoch. Our results demonstrate that shallow inclination may not only result from compaction but may reflect the structure of the geomagnetic field on short time scales. This suggests that secular variation is not averaged out over a time period that covers the Holocene.

Siberian Trap volcanism, global warming and the Permian Triassic mass extinction: New insights from Armenian Permian-Triassic sections: Reply

Article

Jul 2021

Horacek et al. (2021) commented on our publication arguing that we used an incorrect biochronology to define the Permian-Triassic (PT) boundary and that this inaccurate definition resulted in an erroneous interpretation of the oxygen isotope record in the studied Chanakhchi (former Sovestashen) section. Their comment gives us the opportunity to discuss in depth the identification of the PT boundary and to address some of the flawed arguments of Horacek et al.

Jurassic to Cenozoic Magmatic and Geodynamic Evolution of the Eastern Pontides and Caucasus Belts, and Their Relationship With the Eastern Black Sea Basin Opening

Article

Full-text available

Nov 2020

The magmatic arcs of the Eastern Pontides and Lesser Caucasus lie in continuation from one another. A comparison of the subduction related magmatic rocks outcropping throughout this segment of the Northern Tethyan belt exhibits chronological disparities, questioning the common subduction history of the Eastern Pontides and the Lesser Caucasus regions. New data and observations including geochronological and geochemical data, relative to subduction to collision related magmatic rocks argues a novel paleogeographic reconstruction illustrating Mesozoic and Cenozoic evolution of this region. Jurassic to Early Cretaceous arc magmatism runs mainly from the Sochi-Ritsa/Bechasyn regions (Greater Caucasus) towards the south-east to the Alaverdi region and further into the Lesser Caucasus. Late Cretaceous and Cenozoic arc magmatism is evidenced throughout the Eastern Pontides extending through the Bolnisi region to the Lesser Caucasus arc. East to west, Jurassic to Early Cretaceous and Late Cretaceous to Cenozoic portions of arc split to the north and south of the Eastern Black Sea, respectively. Throughout Cretaceous subduction, this segment of the magmatic arc of the Southern Eurasian margin was torn in two due to the oblique opening of the Eastern Black Sea as a back- to intra-arc basin, from west to east. This reconstitution implies that the Jurassic-Early Cretaceous subduction related magmatic rocks of the Greater Caucasus are remnant potions of the Eastern Pontides and Lesser Caucasus arcs. This infers the emplacement of subduction to collision related magmatic rocks throughout the Mesozoic and Cenozoic along the entire Southern Eurasian margin is solely due to a single long-lasting north-dipping subduction.

Jurassic to Cenozoic Magmatic and Geodynamic Evolution of the Eastern Pontides and Caucasus Belts, and Their Relationship With the Eastern Black Sea Basin Opening

Article

Full-text available

Oct 2020
TECTONICS

The magmatic arcs of the Eastern Pontides and Lesser Caucasus lie in continuation from one another. A comparison of the subduction‐related magmatic rocks outcropping throughout this segment of the Northern Tethyan belt exhibits chronological disparities, questioning the common subduction history of the Eastern Pontides and the Lesser Caucasus regions. New data and observations including geochronological and geochemical data, relative to subduction‐ to collision‐related magmatic rocks, argue a novel paleogeographic reconstruction illustrating Mesozoic and Cenozoic evolution of this region. Jurassic to Early Cretaceous arc magmatism runs mainly from the Sochi‐Ritsa/Bechasyn regions (Greater Caucasus) toward the southeast to the Alaverdi region and further into the Lesser Caucasus. Late Cretaceous and Cenozoic arc magmatism is evidenced throughout the Eastern Pontides extending through the Bolnisi region to the Lesser Caucasus arc. East to west, Jurassic to Early Cretaceous and Late Cretaceous to Cenozoic portions of arc split to the north and south of the Eastern Black Sea, respectively. Throughout Cretaceous subduction, this segment of the magmatic arc of the Southern Eurasian margin was torn in two due to the oblique opening of the Eastern Black Sea as a back‐arc to intra‐arc basin, from west to east. This reconstitution implies that the Jurassic‐Early Cretaceous subduction‐related magmatic rocks of the Greater Caucasus are remnant portions of the Eastern Pontides and Lesser Caucasus arcs. This infers the emplacement of subduction‐ to collision‐related magmatic rocks throughout the Mesozoic and Cenozoic along the entire Southern Eurasian margin is solely due to a single long‐lasting north dipping subduction.

Metallogeny of the Tethyan Orogenic Belt: From Mesozoic Magmatic Arcs to Cenozoic Back-Arc and Postcollisional Settings in Southeast Europe, Anatolia, and the Lesser Caucasus: An Introduction

Article

Nov 2019

Introduction The Tethyan mountain ranges stretch from northwestern Africa and western Europe to the southwest Pacific Ocean and constitute the longest continuous orogenic belt on Earth. It is an extremely fertile metallogenic belt, which includes a wide diversity of ore deposit types formed in very different geodynamic settings, which are the source of a wide range of commodities mined for the benefit of society (Janković, 1977, 1997; Richards, 2015, 2016). There are other ore deposit types in this segment of the Tethyan metallogenic belt that are not covered in this special issue, such as bauxite and Ni laterite deposits (Herrington et al., 2016), ophiolite-related chromite deposits (Çiftçi et al., 2019), sedimentary exhalative and Mississippi Valley-type deposits (Palinkaš et al., 2008; Hanilçi et al., 2019), or deposits related to surficial brine processes (Helvacı, 2019).

Cenozoic Strike-Slip Tectonics and Structural Controls of Porphyry Cu-Mo and Epithermal Deposits During Geodynamic Evolution of the Southernmost Lesser Caucasus, Tethyan Metallogenic Belt

Article

Jul 2019

The Zangezur-Ordubad mining district of the southernmost Lesser Caucasus is located in the central segment of the Tethyan metallogenic belt and consists of porphyry Cu-Mo and epithermal Au and base metal systems hosted by the composite Cenozoic Meghri-Ordubad pluton. Ore-hosting structures and magmatic intrusions are predominantly confined to a central N-S–oriented corridor 40 km long and 10 to 12 km wide, located between two regional NNW-oriented right-lateral faults, the Khustup-Giratagh and Salvard-Ordubad faults. The anatomy and kinematics of the main fault network are consistent with dextral strike-slip tectonics controlled by the NNW-oriented Khustup-Giratagh and Salvard-Ordubad faults. Dextral strike-slip tectonics was initiated during the Eocene, concomitantly with final subduction of the Neotethys, and controlled the emplacement of the Agarak, Hanqasar, Aygedzor, and Dastakert porphyry Cu-Mo and Tey-Lichkvaz and Terterasar epithermal Au and base metal deposits. The Eocene structures were repeatedly reactivated during subsequent Neogene evolution in transition to a postsubduction geodynamic setting. Ore-bearing structures at the Oligocene world-class Kadjaran porphyry Cu-Mo deposit were also controlled by dextral strike-slip tectonics, as well as porphyry mineralization and its epithermal overprint hosted by an early Miocene intrusion at Lichk. Eocene to early Miocene dextral strike-slip tectonics took place during NE- to NNE-oriented compression related to Paleogene Eurasia-Arabia convergence and subsequent Neogene postcollision evolution. Paleostress reconstruction indicates major reorganization of tectonic plate kinematics since the early Miocene, resulting in N-S– to NW-oriented compression. Early Miocene epithermal overprint at the Kadjaran porphyry deposit and left-lateral reactivation of faults and mineralized structures are linked to this late Neogene tectonic plate reorganization.

Siberian Trap volcanism, global warming and the Permian-Triassic mass extinction: New insights from Armenian Permian-Triassic sections

Article

Jun 2019

Permian-Triassic boundary sections from Armenia were studied for carbon isotopes of carbonates as well as oxygen isotopes of conodont apatite in order to constrain the global significance of earlier reported variations in the isotope proxies and elaborate the temporal relationship between carbon cycle changes, global warming and Siberian Trap volcanism. Carbon isotope records of the Chanakhchi and Vedi II sections show a 3–5‰ negative excursion that start in the Clarkina nodosa (C. yini) conodont Zone (latest Permian) with minimum values recorded in Hindeodus parvus to Isarcicella isarcica conodont zones (earliest Triassic). Sea surface temperatures (SST) reconstructed from oxygen isotopes of conodont apatite increase by 8–10 °C over an extrapolated time interval of ∼39 ka with the onset of global warming occurring in the C. iranica (C. meishanensis) Zone of the latest Permian. Climate warming documented in the Armenian sections is comparable to published time-equivalent shifts in SST in Iran and South China suggesting that this temperature change represents a true global signature. By correlating the Armenian and Iranian section with the radiometrically well-dated Meishan GSSP (Global Stratotype Section and Point) section (South China), the negative shift in δ13C is estimated to have occurred 12–128 ka prior to the onset of global warming. This temporal offset is unexpected given the synchrony in changes in atmospheric CO2 and global temperature as seen in Pleistocene ice core records. The negative δ13C excursion is explained by the addition of emission of isotopically light CO2 and CH4 from thermogenic heating of organic carbon-rich sediments by Siberian Trap sill intrusions. However, the observed time lag in the δ13C and δ18O shifts questions the generally assumed cause-effect relationship between emission of thermogenically produced greenhouse gases and global warming. The onset of temperature rise coincides with a significant enrichment in Hg/TOC (total organic carbon) ratios arguing for a major volcanic event at the base of the extinction interval. Whether global warming was a major factor for the Late Permian mass extinction depends on the duration of the extinction interval. Warming only starts at the base of the extinction interval, but with the extinction encompassing a time interval of 60 ± 48 ka, global climate warming in conjunction with temperature-related stressors as hypoxia and reduced nutrient availability may have been one of the major triggers of the most devastating biotic crisis in Earth history.

Diachronous demise of the Neotethys Ocean as a driver for non-cylindrical orogenesis in Anatolia

Article

Full-text available

Jun 2019
TECTONOPHYSICS

Continent-continent collision drives crustal deformation, topographic rise, and geodynamic change. Africa-Eurasia convergence accommodated in the Eastern Mediterranean involved subduction of the Neotethyan oceanic lithosphere in Anatolia. Subduction was followed by collision of continental crust of Greater Adria with Eurasia to form the Izmir-Ankara-Erzincan suture zone. Discerning the effects of this collision from pre-collisional ophiolite obduction-related orogeny of Greater Adria is notoriously difficult. Estimates on the timing of collision in Central Anatolia are based on a forearc-to-foreland basin transition along the Eurasian margin and suggest a ~60 Ma age of initial collision. Here we assess whether this age is also representative of collision in Eastern Anatolia and across the Cenozoic Sivas Basin that straddles the Greater Adria-Europe suture. To this end we retro-deform regional block rotations in the Pontides, the Kırşehir Block, and the Taurides, building a first order regional ‘block circuit’ around the Sivas Basin. We show that up to ~700 km of convergence must have been accommodated across the Sivas Basin after Central Anatolian Kırşehir-Pontide collision at ~60 Ma – an order of magnitude of crustal shortening more than estimated, and wholesale lithospheric subduction must have occurred throughout much of the Cenozoic. Paleocene collision would require that this subduction consumed continental lithosphere, which is unlikely. We consequently infer that oceanic subduction continued much longer in Eastern Anatolia, perhaps well into the Miocene. We postulate that prolonged oceanic subduction and slab pull drew the Eastern Taurides north relative to the Central Taurides, leading to shortening and oroclinal bending in Central Anatolia. The diachronous demise of the Neotethys Ocean in Anatolia, as a function of its paleogeography, is thus a likely driver for the strong non-cylindricity of the Cenozoic Anatolian collisional orogen.

Reply to Comment by Vincent et al.

Article

Feb 2018

Key Points The Greater Caucasus Basin encompassed a broader region than envisioned by Vincent et al., who disregard Cenozoic shortening Terminal basin closure occurred when the Greater and Lesser Caucasus collided Data cited by Vincent et al. document the onset of basin closure by 35 Ma, but do not indicate terminal basin closure at this time

The Permian-Triassic transition in Southern Armenia.

Book

Full-text available

Oct 2017

The Southern Caucasus region is one of the few places in the World where continuous successions of Upper Permian and Lower Triassic strata with marine fauna can be observed at outcrop. Field Guide Book, p. 1-53.

Active tectonics of central-western Caucasus, Georgia

Article

Oct 2016
TECTONOPHYSICS

This work contributes to a better knowledge of potentially seismogenic faults of the Georgia Greater and Lesser Caucasus by evaluating the distribution of earthquake foci, active tectonic stress field, kinematics and geometry of main fault planes. We consider all the information coming from field structural geology, geomorphology, seismological data from historical and instrumental catalogues, seismic reflection sections, as well as new focal mechanism solutions. These data enable recognizing some active ENE-WSW reverse faults in the core of the Greater Caucasus that are parallel to the mountain range. At the southernmost front of the Greater Caucasus, a series of main thrusts dipping towards NNE are active, with up to hundreds-km-long segments; along this thrust zone, a potentially locked segment is present, about 90 km long. The studied section of the Lesser Caucasus has active structures along the northern front given by south-dipping thrusts, as well as in the central core where strike-slip and oblique faults coexist. The Transcaucasian depression between the two mountain ranges shows an ongoing inversion tectonics of the central part of the Rioni Basin where active N- to NE-dipping reverse faults are present, accompanied by clear evidence of uplift of a wide area. The data are coherent with a N-S to NNE-SSW contraction of the central-western Greater Caucasus and Lesser Caucasus. Although in general the seismicity decreases westward in terms of number of earthquakes and magnitude, seismological and geological structural data in the Rioni Basin indicate here a Quaternary propagation of deformation towards the west.

Subduction & orogeny: Introduction to the special volume

Article

Full-text available

May 2016

Subduction processes play a major role in plate tectonics and the subsequent geological evolution of Earth. This special issue focuses on ongoing research in subduction dynamics to a large extent (oceanic subduction, continental subduction, obduction…) for both past and active subduction zones and into mountain building processes and the early evolution of orogens. It puts together various approaches combining geophysics (imaging of subduction zones), petrology/geochemistry (metamorphic analysis of HP-UHP rocks, fluid geochemistry and magmatic signal, geochronology), seismology and geodesy (present-day evolution of subduction zones, active tectonics), structural geology (structure and evolution of mountain belts), and numerical modelling to provide a full spectrum of tools that can be used to constrain the nature and evolution of subduction processes and orogeny. Studies presented in this special issue range from the long-term (orogenic cycle) to short-term (seismic cycle).

J. of Geodynamics Subduction and Orogeny 2016

Data

Full-text available

May 2016

Subduction & Orogeny: Introduction to the Special volume

Article

Full-text available

Mar 2016
J GEODYN

Geochemistry of the Eocene magmatic rocks from the Lesser Caucasus area (Armenia): Evidence of a subduction geodynamic environment

Article

Full-text available

Feb 2016

Abstract: This paper is focused on petrological and geochemical data obtained on a series of Middle and Upper Eocene magmatic rocks from the Lesser Caucasus of Armenia in order to elucidate magma sources and geodynamic processes. Middle–Upper Eocene magmatism is present in two main zones: the Amasia–Sevan–Hakari suture zone (ASHSZ) and the so-called South Armenian Microplate (SAM). Volcanic rocks from both places range from basalt to rhyolite and mostly display a calc-alkaline character. Trace element patterns from the SAM and ASHSZ samples show mobile-elements enrichment (Rb, Ba, Th) together with strong negative high field strength elements (Nb, Ta, Hf, Zr) anomalies. The (La/Sm)N ratio yields very close values for both areas. Conversely, the (La/Yb)N ratio is, on average, significantly higher for SAM than for ASHSZ, suggesting the presence of residual garnet at the source of the SAM volcanic rocks. Nevertheless, trace elements suggest partial melting from phlogopite- and amphibole-bearing spinel lherzolitic mantle sources. Neodymium and strontium isotopes yield 1Nd(40Ma) and 87Sr/86Sr(40Ma) ratios ranging, respectively, from –0.3 to +6.6 and from 0.70314 to 0.70531 for SAM samples, and from +3.4 to +6.8 and from 0.70393 to 0.70433 for ASHSZ samples. Initial Pb/Pb isotopic ratios yield close values for both areas but with slightly higher and more homogeneous 207Pb/204Pb and 208Pb/204Pb ratios for SAM samples. Such features concur with a more pronounced slabcomponent contribution in the frontal part of the volcanic belt, that is, in the SAM domain. No significant crustal contamination has been detected in the studied Eocene magmatic rocks from both the ASHSZ and SAM. Considering geodynamic and geochemical constraints, we propose that this magmatism is connected with a north-dipping Southern Neotethys subduction, in an extensional (back-arc) environment of orogenic belts. The Arabia–Eurasia collision and the closure of the Neotethys Ocean may have occurred after this magmatic event.

The eastern Black Sea-Caucasus region during the Cretaceous: New evidence to constrain its tectonic evolution

Article

Full-text available

Dec 2015
CR GEOSCI

Abstract We report new observations in the Eastern Black Sea-Caucasus region that allow reconstructing the evolution of the Neotethys in the Cretaceous. At that time, the Neotethys oceanic plate was subducting northward below the continental Eurasia plate. Based on the analysis of the obducted ophiolites that crop out throughout Lesser Caucasus and East Anatolides, we show that a spreading center (AESA basin) existed within the Neotethys, between Middle Jurassic and Early Cretaceous. Later, the spreading center was carried into the subduction with the Neotethys plate. We argue that the subduction of the spreading center opened a slab window which allowed asthenospheric material to move upward, in effect thermally and mechanically weakening the otherwise strong Eurasia upper plate. The local weakness zone favored the opening of the Black Sea back-arc basins. Later, in the Late Cretaceous, the AESA basin obducted onto the Taurides-Anatolides-South Armenia Microplate (TASAM), which then collided with Eurasia along a single suture zone (AESA suture).

Uppermost Permian to Lower Triassic conodont biostratigraphy and carbon isotope records from Southern Armenia

Article

Mar 2025
PALAEOGEOGR PALAEOCL

Geochemical insights and petrogenetic processes of ophiolitic fragments from Avajiq and Silvana: implications for Neo-Tethyan Evolution in northwest Iran

Article

Full-text available

Jan 2025
INT GEOL REV

ABSTRACT The Avajiq and Silvana ophiolites are part of the Late Cretaceous Neo-Tethyan ophiolitic belt located in northwestern Iran, between the Sevan-Akera suture to the north and the Bitlis-Zagros suture in the southwest. The Avajiq ophiolite formed between the South Armenian Block (SAB) with a Gondwanan origin to the north and the Eastern Anatolian Plateau (EAP) to the south and west. In contrast, the Silvana ophiolite is situated at the juncture of the EAP and the Sanandaj-Sirjan Zone (SaSiZ). The mantle sequences of both ophiolites are composed of harzburgites with various degrees of refertilization. The compositions of olivine (Fo: 90–90.8), spinel (Mg#: 0.49 to 0.69 and Cr#: 0.25 to 0.59), orthopyroxene (Mg#: 0.90–0.96), and clinopyroxene (Mg#: 0.91–0.94), along with the bulk geochemistry of highly serpentinized ultramafic rocks, were evaluated to distinguish the tectonic settings of both ophiolites. The spinel composition indicates that the harzburgites represent mantle residuum formed after moderate to high degrees of partial melting (16–19% for the Avajiq and 10–17% for the Silvana). This is supported by the low bulk rock content of incompatible elements such as Ti and heavy rare earth elements (REE). Harzburgites generally display U-shaped chondrite-normalized REE patterns, with elevated light REE (LaN/SmN = 3.5–4), reflecting early partial melting events and multiple episodes of depletion, modified by subsequent melt/fluid-dominated metasomatism. The observed moderate to significant enrichment in fluid-mobile elements, such as U, Pb, Ba, and Sr, in the harzburgites are linked to serpentinization/refertilization resulting from fluid/melt-rock interactions. Field relationship and geochemical comparisons with other Neo-Tethyan ophiolites suggest that most samples from the Silvana ophiolite along with those from the Zagros ophiolites, predominantly exhibit abyssal characteristics, although some may be more closely related to fore-arc settings. In contrast, the Avajiq fore-arc ophiolite is associated with the Khoy-Maku back-arc basin, situated far from the southern and northern Neo-Tethyan sutures.

Magmatic record along the Eastern Pontides-Lesser Caucasus orogenic belt: Implications for magma petrogenesis, regional tectonics and metallogeny

Article

Oct 2023
EARTH-SCI REV

THORIUM -THE ENERGY SOURCE OF THE FUTURE AND ITS ORE OCCURRENCES IN GEORGIA

Book

Full-text available

Jul 2023

Synthesis of micropaleontological age constraints for the reconstruction of the Tethyan realm in the Lesser Caucasus (Armenia, Karabagh)

Article

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Apr 2023

Thorium - the Energy Source of the Future and its Ore Occurrences in Georgia

Book

Full-text available

Aug 2022

The first part of the book discusses the energy potential of thorium and future prospects. Many researchers believe that thorium is the nuclear energy source that, without CO2 emissions, can fill the energy shortfall caused by the depletion of hydrocarbons in the future. Therefore almost all developed countries in the world are currently working on the creation of thorium-powered generators and increasing its reserves. For a number of reasons, this important global issue has not yet been discussed at the state level in Georgia. Hence, for the first time in Georgia, we tried to explore thorium ore occurrences and evaluate the potential of its resources. The second part of the book discusses the results of this research in detail.

Thorium - the Energy Source of the Future and its Ore Occurrences in Georgia

Book

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Aug 2022

Phosphorus Cycle and Primary Productivity Changes in the Tethys Ocean During the Permian-Triassic Transition: Starving Marine Ecosystems

Article

Full-text available

Mar 2022

The ultimate cause(s) of the end-Permian mass extinction (∼252 Ma ago) has been disputed. A complex interplay of various effects, rather than a single, universal killing mechanism, were most likely involved. Climate warming as consequence of greenhouse gas emissions by contemporaneous Siberian Traps volcanism is widely accepted as an initial trigger. Synergetic effects of global warming include increasing stratification of the oceans, inefficient water column mixing, and eventually low marine primary productivity culminating in a series of consequences for higher trophic levels. To explore this scenario in the context of the end-Permian mass extinction, we investigated sedimentary total organic carbon, phosphorus speciation as well as nickel concentrations in two low-latitude Tethyan carbonate sections spanning the Permian-Triassic transition. Total organic carbon, reactive phosphorus and nickel concentrations all decrease in the latest Permian and are low during the Early Triassic, pointing to a decline in primary productivity within the Tethyan realm. We suggest that the productivity collapse started in the upper C. yini conodont Zone, approximately 30 ka prior to the main marine extinction interval. Reduced primary productivity would have resulted in food shortage and thus may serve as explanation for pre-mass extinction perturbations among marine heterotrophic organisms.

Lower Famennian (Upper Devonian) rhynchonellide and athyride brachiopods from the South Armenian Block

Article

Full-text available

Feb 2021

The lower Famennian ‘ Cyrtospirifer ’ orbelianus brachiopod Zone established in Armenia by Abrahamyan (1957) (coeval to the crepida conodont Zone) contains an abundant and diverse brachiopod fauna that still remains poorly studied. In an effort to revise and update its systematic classification and to assess the brachiopod diversity in this area after the Kellwasser extinction event at the end of the Frasnian, our attention is here focused on rhynchonellides and athyrides. Six rhynchonellide species are described belonging to five genera as well as a single athyride species ( Crinisarina pseudoglobularis n. sp.), which is new to science. The genus Crinisarina is reported for the first time in the South Armenian Block (SAB), which was then part of the northern margin of Gondwana. Some of the rhynchonellides identified were previously recognized in this area, but they require modern documentation and taxonomic reassessment. More particularly, it is the first time that the internal structure of Sartenaerus baitalensis (Reed, 1922) is illustrated, taking into account that it is the type species of a biostratigraphically significant Famennian genus. One of the oldest punctate rhynchonellide species, Greira transcaucasica Erlanger, 1993, is described for the first time from Armenia and its intraspecific morphological variability is documented quantitatively. From a paleobiogeographic viewpoint, the studied brachiopod fauna clearly shares affinities with contemporaneous ones from other regions of the Gondwanan northern margin that extend eastwards of the SAB to Afghanistan and Pamir, although there are also some endemic elements. UUID: http://zoobank.org/798eb5f9-ad15-4d90-bc6a-ff22ee936438

Reliability of palaeomagnetic poles from sedimentary rocks

Article

Full-text available

Feb 2021

Palaeomagnetic poles form the building blocks of apparent polar wander paths and are used as primary input for quantitative palaeogeographic reconstructions. The calculation of such poles requires that the short-term, palaeosecular variation (PSV) of the geomagnetic field is adequately sampled and averaged by a palaeomagnetic dataset. Assessing to what extent PSV is recorded is relatively straightforward for rocks that are known to provide spot readings of the geomagnetic field, such as lavas. But it is unknown whether and when palaeomagnetic directions derived from sedimentary rocks represent spot readings of the geomagnetic field and sediments are moreover suffering from inclination shallowing, making it challenging to assess the reliability of poles derived from these rocks. Here, we explore whether a widely used technique to correct for inclination shallowing, known as the elongation-inclination (E/I) method, allows us to formulate a set of quality criteria for (inclination shallowing-corrected) palaeomagnetic poles from sedimentary rocks. The E/I method explicitly assumes that a sediment-derived dataset provides, besides flattening, an accurate representation of PSV. We evaluate the effect of perceived pitfalls for this assumption using a recently published dataset of 1275 individual palaeomagnetic directions of a >3 km-thick succession of ~69-41.5 Ma red beds from the Gonjo Basin (eastern Tibet), as well as synthetic data generated with the TK03.GAD field model. The inclinations derived from the uncorrected dataset are significantly lower than previous estimates for the basin, obtained using coeval lavas, by correcting inclination shallowing using anisotropy-based techniques, and by predictions from tectonic reconstructions. We find that the E/I correction successfully restores the inclination to values predicted by these independent datasets if the following conditions are met: the number of directions N is at least 100, the A95 cone of confidence falls within a previously defined A95min-max reliability envelope, no negative reversal test is obtained and vertical-axis rotation differences within the dataset do not exceed 15°. We propose a classification of three levels (A, B, and C) that should be applied after commonly applied quality criteria for palaeomagnetic poles are met. For poles with classification ‘A’, we find no reasons to assume insufficient quality for tectonic interpretation. Poles with classification ‘B’ could be useful, but have to be carefully assessed, and poles with classification ‘C’ provide unreliable palaeolatitudes. We show that application of these criteria for datasets of other sedimentary rock types classifies datasets whose reliability is independently confirmed as ‘A’ or ‘B’, and that demonstrably unreliable datasets are classified as ‘C’, confirming that our criteria are useful, and conservative. The implication of our analysis is that sediment-based datasets of quality ‘A’ may be considered statistically equivalent to datasets of site-mean directions from rapidly cooled igneous rocks like lavas and provide high-quality palaeomagnetic poles.

Active Kinematics of the Greater Caucasus from Seismological and GPS Data: A Review

Chapter

Jan 2021

Active stress field and fault kinematics of the Greater Caucasus

Article

Nov 2019
J ASIAN EARTH SCI

This work contributes to depict the current seismicity, fault kinematics, and state of stress in the Greater Caucasus (territories of Georgia, Azerbaijan and Russia). We merged and homogenized data from diﬀerent earthquake catalogues, relocated ~1000 seismic events, created a database of 366 selected focal mechanism solutions, 239 of which are new, and performed a formal stress inversion. Preferential alignments of crustal earthquake foci indicate that most seismic areas are located along the southern margin of the belt and in the north-eastern sector. This is consistent with the presence of dominant active WNW-ESE faults, parallel to the mountain range. In the entire Greater Caucasus, a dominant NNE-SSW-oriented greatest principal stress (σ 1 ) controls the over-all occurrence of earthquakes of minor and major magnitude. Main earthquakes are char- acterized by a vertical least principal stress (σ 3), corresponding to reverse kinematics. Reverse slip is more common along the southwestern and north-eastern foothills of the Greater Caucasus, although in these areas there are also scattered strike-slip events. This suggests the presence of local stress ﬁelds with horizontal σ 1 and σ 3 . In the central-southern part of the mountain belt, in correspondence of the local collision between the Lesser and the Greater Caucasus, σ 1 rotates to NNW-SSE. The strike-slip events, instead, dominate along the southern ﬂank of the central-eastern mountain range; this is interpreted as the eﬀect of the collision that promotes eastward escape of the tectonic blocks located to the east.

Orogenic architecture of the Mediterranean region and kinematic reconstruction of its tectonic evolution since the Triassic

Article

Full-text available

May 2020
GONDWANA RES

The basins and orogens of the Mediterranean region ultimately result from the opening of oceans during the early break-up of Pangea since the Triassic, and their subsequent destruction by subduction accommodating convergence between the African and Eurasian Plates since the Jurassic. The region has been the cradle for the development of geodynamic concepts that link crustal evolution to continental break-up, oceanic and continental subduction, and mantle dynamics in general. The development of such concepts requires a first-order understanding of the kinematic evolution of the region for which a multitude of reconstructions have previously been proposed. In this paper, we use advances made in kinematic restoration software in the last decade with a systematic reconstruction protocol for developing a more quantitative restoration of the Mediterranean region for the last 240 million years. This restoration is constructed for the first time with the GPlates plate reconstruction software and uses a systematic reconstruction protocol that limits input data to marine magnetic anomaly reconstructions of ocean basins, structural geological constraints quantifying timing, direction, and magnitude of tectonic motion, and tests and iterations against paleomagnetic data. This approach leads to a reconstruction that is reproducible, and updatable with future constraints. We first review constraints on the opening history of the Atlantic (and Red Sea) oceans and the Bay of Biscay. We then provide a comprehensive overview of the architecture of the Mediterranean orogens, from the Pyrenees and Betic-Rif orogen in the west to the Caucasus in the east and identify structural geological constraints on tectonic motions. We subsequently analyze a newly constructed database of some 2300 published paleomagnetic sites from the Mediterranean region and test the reconstruction against these constraints. We provide the reconstruction in the form of 12 maps being snapshots from 240 to 0 Ma, outline the main features in each time-slice, and identify differences from previous reconstructions, which are discussed in the final section.

Landslides near Enguri dam (Caucasus, Georgia) and possible seismotectonic effects

Article

Full-text available

Jan 2019
NAT HAZARD EARTH SYS

The Enguri dam and water reservoir, nested in the southwestern Caucasus (Republic of Georgia), are surrounded by steep mountain slopes. At a distance of 2.5 km from the dam, a mountain ridge along the reservoir is affected by active deformations with a double vergence. The western slope, directly facing the reservoir, has deformations that affect a subaerial area of 1.2 km2. The head scarp affects the Jvari–Khaishi–Mestia main road with offsets of man-made features that indicate slip rates of 2–9 cm yr-1. Static, pseudostatic and Newmark analyses, based on field and seismological data, suggest different unstable rock volumes based on the environmental conditions. An important effect of variation of the water table is shown, as well as the possible destabilization of the slope following seismic shaking, compatible with the expected local peak ground acceleration. This worst-case scenario corresponds to an unstable volume on the order of up to 48±12×106 m3. The opposite, eastern slope of the same mountain ridge is also affected by wide deformation affecting an area of 0.37 km2. Here, field data indicate 2–5 cm yr-1 of slip rates. All this evidence is interpreted as resulting from two similar landslides, whose possible causes are discussed, comprising seismic triggering, mountain rapid uplift, river erosion and lake variations.

Landsliding near Enguri dam (Caucasus, Georgia) and possible seismoectonic effects

Article

Full-text available

Aug 2018

The Enguri dam and water reservoir, nested in southwestern Caucasus (Republic of Georgia), are surrounded by steep mountain slopes. At a distance of 2.5km from the dam, a mountain ridge along the reservoir is affected by active deformations with a double vergence. The western slope, directly facing the reservoir, has deformations that involve a subaerial area of 1.2km². The head scarp interests the main Jvari–Khaishi–Mestia road with offset of man-made features that indicate slip rates of 2–9cm/y. Static, pseudostatic and Newmark numerical analyses, based on field and seismological data, suggest different unstable rock volumes basing on the environment conditions. An important effect of variation of water table is showed, as well as the possible destabilization of the landslide following seismic shaking compatible with the expected local Peak Ground Acceleration. This worst scenario corresponds to an unstable volume in the order of up to 48±12*10⁶m³. The opposite, eastern slope of the same mountain ridge is also affected by wide deformation involving an area of 0.37km². Here, field data indicate 2–5cm/y of short-term and long-term slip rates. Ground Penetrating Radar surveys of the head scarps confirm that these slip planes are steep and extend downward. All these evidences are interpreted as resulting from two similar landslides, whose possible causes are discussed, comprising seismic triggering, mountain rapid uplift, river erosion and lake variations.

Relict basin closure and crustal shortening budgets during continental collision: An example from Caucasus sediment provenance

Article

Nov 2016

Comparison of plate convergence with the timing and magnitude of upper-crustal shortening in collisional orogens indicates both shortening deficits (200-1700 km) and significant (10-40%) plate deceleration during collision, the cause(s) for which remain debated. The Greater Caucasus Mountains, which result from post-collisional Cenozoic closure of a relict Mesozoic back-arc basin on the northern margin of the Arabia-Eurasia collision zone, help reconcile these debates. Here we use U-Pb detrital zircon provenance data and the regional geology of the Caucasus to investigate the width of the now-consumed Mesozoic back-arc basin and its closure history. The provenance data record distinct southern and northern provenance domains that persisted until at least the Miocene. Maximum basin width was likely ~350-400 km. We propose that closure of the back-arc basin initiated at ~35 Ma, coincident with initial (soft) Arabia-Eurasia collision along the Bitlis-Zagros suture, eventually leading to ~5 Ma (hard) collision between the Lesser Caucasus arc and the Scythian platform to form the Greater Caucasus Mountains. Final basin closure triggered deceleration of plate convergence and tectonic reorganization throughout the collision. Post-collisional subduction of such small (102-103 km wide) relict ocean basins can account for both shortening deficits and delays in plate deceleration by accommodating convergence via subduction/underthrusting, although such shortening is easily missed if it occurs along structures hidden within flysch/slate belts. Relict-basin closure is likely typical in continental collisions in which the colliding margins are either irregularly shaped or rimmed by extensive back-arc basins and fringing arcs, such as those in the modern South Pacific.

Obduction of old oceanic lithosphere due to reheating and plate reorganization: Insights from numerical modelling and the NE Anatolia - Lesser Caucasus case example

Article

Full-text available

Feb 2016
J GEODYN

The ophiolites of NE Anatolia and of the Lesser Caucasus (NALC) evidence an obduction over ~200 kilometres of an oceanic lithosphere of Middle Jurassic age (c. 175-165 Ma) along an entire tectonic boundary (> 1000 km) at around 90 Ma. The obduction process is characterized by four first order geological constraints: (1) Ophiolites represent remnants of a single ophiolite nappe currently of only a few kilometres thick and 200 km long. The oceanic crust was old (~80 Ma) at the time of its obduction. (2) The presence of OIB-type magmatism emplaced up to 10 Ma prior to obduction preserved on top of the ophiolites is indicative of mantle upwelling processes (hotspot). (3) The leading edge of the Taurides-Anatolides, represented by the South Armenian Block, did not experience pressures exceeding 0.8 GPa nor temperatures larger than ~300°C during underthrusting below the obducting oceanic lithosphere. (4) An oceanic domain of a maximum 1000 km (from north to south) remained between Taurides-Anatolides and Pontides-Southern Eurasian Margin after the obduction. We employ two-dimensional thermo-mechanical numerical modelling in order to investigate obduction dynamics of a re-heated oceanic lithosphere. Our results suggest that thermal rejuvenation (i.e. reheating) of the oceanic domain, tectonic compression, and the structure of the passive margin are essential ingredients for enabling obduction. Afterwards, extension induced by far-field plate kinematics (subduction below Southern Eurasian Margin), facilitates the thinning of the ophiolite, the transport of the ophiolite on the continental domain, and the exhumation of continental basement through the ophiolite. The combined action of thermal rejuvenation and compression are ascribed to a major change in tectonic motions occurring at 110-90 Ma, which led to simultaneous obductions in the Oman (Arabia) and NALC regions.

N.A. Imamverdiyev et al. - Formation of the Late Cenozoic volcanic complexes of the Lesser Caucasus

Data

Full-text available

Jan 2017

Article - Formation of the Late Cenozoic volcanic complexes of the Lesser Caucasus - Abstract to this article in - Geotectonics 2017 = ISSN 0016-8521, Geotectonics, 2017, Vol. 51, No. 5, pp. 489–498. © Pleiades Publishing, Inc., 2017. - ( Formation of the Late Cenozoic volcanic complexes of the Lesser Caucasus Data) by - N.A. Imamverdiyev, V.M. Baba-zade, A. Romanko, Sh. Abdullayeva, M. Gasangulieva, G. Babaeva, A. Veliev. Abstract The paper considers the role of the lithospheric mantle and asthenosphere during the Late Cenozoic collision volcanism of the Lesser Caucasus. The results of petrogeochemical studies show that the products of volcanism of the West Volcanic Zone of Armenia and the calc-alkaline andesite–dacite–rhyodacite complex of the Neogene Kelbadzhar and Karabakh plateaus were formed from an enriched source in a suprasubduction setting. Late Pliocene–Quaternary moderately alkaline and alkaline volcanic rocks of the Lesser Caucasus differ in petrogeochemistry from suprasubduction volcanic rocks. In trace element contents and patterns, they are similar to rocks formed from an enriched mantle source. Comparative analysis of the geological and geophysical data suggests the model of lithospheric slab break-off of the thickened lithosphere as the triggering mechanism for Late Cenozoic magmatism of the Lesser Caucasus. Keywords Lesser Caucasus Late Cenozoic collision volcanism petrogeochemistry lithospheric mantle asthenosphere slab break-off of lithosphere seismic tomography

Geology of the Caucasus: A Review

Article

Full-text available

Jan 2011

The structure and geological history of the Caucasus are largely determined by its position between the stillconverging Eurasian and Africa-Arabian lithospheric plates, within a wide zone of continental collision. During the Late Proterozoic-Early Cenozoic, the region belonged to the Tethys Ocean and its Eurasian and Africa-Arabian margins where there existed a system of island arcs, intra-arc rift s, back-arc basins characteristic of the pre-collisional stage of its evolution of the region. The region, along with other fragments that are now exposed in the Upper Precambrian- Cambrian crystalline basement of the Alpine orogenic belt, was separated from western Gondwana during the Early Palaeozoic as a result of back-arc rift ing above a south-dipping subduction zone. Continued rift ing and seafloor spreading produced the Palaeotethys Ocean in the wake of northward migrating peri-Gondwanan terranes. The displacement of the Caucasian and other peri-Gondwanan terranes to the southern margin of Eurasia was completed by ~350 Ma. Widespread emplacement of microcline granite plutons along the active continental margin of southern Eurasia during 330-280 Ma occurred above a north-dipping Palaeotethyan subduction zone. However, Variscan and Eo-Cimmerian-Early Alpine events did not lead to the complete closing of the Palaeozoic Ocean. The Mesozoic Tethys in the Caucasus was inherited from the Palaeotethys. In the Mesozoic and Early Cenozoic, the Great Caucasus and Transcaucasus represented the Northtethyan realm - the southern active margin of the Eurasiatic lithospheric plate. The Oligocene-Neogene and Quaternary basins situated within the Transcaucasian intermontane depression mark the syn- and post-collisional evolution of the region; these basins represented a part of Paratethys and accumulated sediments of closed and semiclosed type. The final collision of the Africa-Arabian and Eurasian plates and formation of the present-day intracontinental mountainous edifice of the Caucasus occurred in the Neogene-Quaternary period. From the Late Miocene (c. 9-7 Ma) to the end of the Pleistocene, in the central part of the region, volcanic eruptions in subaerial conditions occurred simultaneously with the formation of molasse troughs. The geometry of tectonic deformations in the Transcaucasus is largely determined by the wedge-shaped rigid Arabian block intensively indenting into the Asia Minor-Caucasian region. All structural-morphological lines have a clearly-expressed arcuate northward-convex configuration reflecting the contours of the Arabian block. However, farther north, the geometry of the fold-thrust belts is somewhat different - the Achara-Trialeti fold-thrust belt is, on the whole, W-E-trending; the Greater Caucasian fold-thrust belt extends in a WNW-ESE direction.

Palaeotectonic maps of the Middle East : Tectono-Sedimentary-Palinspastic maps from Late Norian to Pliocene

Article

Full-text available

Jan 2008

Atlas of 14 maps at 1/18 500 000. Publisher CGMW, Paris, France

Chondrichthyan microfossils from the Famennian and Tournaisian of Armenia

Article

Full-text available

Jan 2011

The assemblages of chondrichthyan microremains from the Famennian of Armenia show great resemblances to those from central iran. particularly, the very rich sample (almost 200 teeth) from the lower Famennian of ertych contains a fauna similar to that from the iranian section of hutk, and the sample from the upper Famennian of khor Virap has its counterpart in the sample from dalmeh, iran. only one chondrichthyan taxon definitely unknown from iran, Ertychius intermedius gen. et sp. nov., was recorded. The other newly described species, Lissodus lusavorichi sp. nov., was noted earlier from dalmeh, but at that time was left unnamed. it appears that the same type of relatively shallow marine environment predominated in the central and north-western parts of the iranian platform during the Famennian and that in a given time-interval the same type of ichthyofauna was distributed throughout the area. The single lower Tournaisian sample from the sevakavan section yielded a peculiar form of thrinacodont teeth, possibly intermediate between Thrinacodus tranquillus and Th. ferox.

Geological history of ophiolites in the Lesser Caucasus and correlation with the Izmir-Ankara-Erzincan suture zone: insights from radiolarian biochronology

Article

Full-text available

Sep 2012

Three distinct radiolarian assemblages were obtained in this study; two of them were extracted from large blocks of radiolarites included in a mélange NW of Lake Sevan (Dzknaget). The latest Tithonian-Late Valanginian assemblage comes from a coherent sequence of 6–7 m-thick radiolarites with intercalations of lavas and rounded blocks of shallow-water limestones. The Late Barremian-Early Aptian assemblage found in the second block allows correlation with radiolarites dated recently in Karabagh. A third radiolarian assemblage comes from Vedi and establishes that radiolarian ooze was accumulated in the Tethyan realm of the Lesser Caucasus until at least the middle Albian. A synthesis of all available micropaleontological (radiolarian) and geochronological ages for the ophiolites present in Armenia and Karabagh points to the following scenario for their geological evolution: the initial phase of oceanic floor spreading was under way during the Late Triassic (Carnian) or even slightly before; the bulk of oceanic lithosphere preserved today in the Lesser Caucasus was formed during the Jurassic; evidence for subaerial volcanic activity is recorded in tuffite intercalations in the Middle-Upper Jurassic radiolarian cherts; an oceanic volcanic plateau was formed during the Late Barremian-Aptian (or possibly even before) while the obduction of ophiolites took place during the Coniacian-Santonian. The geological history of ophiolites in the Lesser Caucasus shares a number of similarities with the Izmir-Ankara-Erzincan suture zone (i.e. initiation of ocean spreading during the Carnian, obduction after the Cenomanian), but there are also some differences especially with respect to the timing of the oceanic plateau emplacement.

Pervasive Paleogene remagnetization of the central Taurides fold-and-thrust belt (southern Turkey) and implications for rotations in the Isparta Angle

Article

Full-text available

Mar 2011
GEOPHYS J INT

The Turkish Anatolide–Tauride block rifted away from the northern margin of Gondwana in the Triassic, which gave way to the opening of the southern Neo-Tethys. By the late Palaeocene to Eocene, it collided with the southern Eurasian margin, leading to the closure of the northern Neo-Tethys ocean. To determine the position of the Anatolide–Tauride block with respect to the African and Eurasian margin we carried out a palaeomagnetic study in the central Taurides belt, which constitutes the eastern limb of the Isparta Angle. The sampled sections comprise Carboniferous to Palaeocene rocks (mainly limestones). Our data suggest that all sampled rocks are remagnetized during the late Palaeocene to Eocene phase of folding and thrusting event, related to the collision of the Anatolide–Tauride block with Eurasia. To further test the possibility of remagnetization, we use a novel end-member modelling approach on 174 acquired isothermal remanent magnetization (IRM) curves. We argue that the preferred three end-member model confirms the proposed remagnetization of the rocks. Comparing our data to the post-Eocene declination pattern in the central Tauride belt, we conclude that our clockwise rotations are in agreement with data from other studies. After combining our results with previously published data from the Isparta Angle (that includes our study area), we have reasons to cast doubt on the spatial and temporal extent of an earlier reported early to middle Miocene remagnetization event. We argue that the earlier reported remagnetized directions from Triassic rocks—in tilt corrected coordinates—from the southwestern Antalya Nappes (western Taurides), are in good agreement with other studies from the area that show a primary origin of their characteristic remanent magnetization. This implies that we document a clockwise rotation for the southwestern Antalya Nappes since the Triassic that is remarkably similar to the post-Eocene (∼40°) rotation of the central Taurides. For the previously published results that are clearly remagnetized, we argue that their remagnetization has occurred in the Palaeocene to Eocene.

Subduction, ophiolite genesis and collision history of Tethys adjacent to the Eurasian continental margin: New evidence from the Eastern Pontides, Turkey

Article

Full-text available

May 2014

This paper presents several types of new information including U–Pb radiometric dating of ophiolitic rocks and an intrusive granite, micropalaeontological dating of siliceous and calcareous sedimentary rocks, together with sedimentological, petrographic and structural data. The new information is synthesised with existing results from the study area and adjacent regions (Central Pontides and Lesser Caucasus) to produce a new tectonic model for the Mesozoic–Cenozoic tectonic development of this key Tethyan suture zone. The Tethyan suture zone in NE Turkey (Ankara–Erzincan–Kars suture zone) exemplifies stages in the subduction, suturing and post-collisional deformation of a Mesozoic ocean basin that existed between the Eurasian (Pontide) and Gondwanan (Tauride) continents. Ophiolitic rocks, both as intact and as dismembered sequences, together with an intrusive granite (tonalite), formed during the Early Jurassic in a supra-subduction zone (SSZ) setting within the İzmir–Ankara–Erzincan ocean. Basalts also occur as blocks and dismembered thrust sheets within Cretaceous accretionary melange. During the Early Jurassic, these basalts erupted in both a SSZ-type setting and in an intra-plate (seamount-type) setting. The volcanic-sedimentary melange accreted in an open-ocean setting in response to Cretaceous northward subduction beneath a backstop made up of Early Jurassic forearc ophiolitic crust. The Early Jurassic SSZ basalts in the melange were later detached from the overriding Early Jurassic ophiolitic crust. Sedimentary melange (debris-flow deposits) locally includes ophiolitic extrusive rocks of boninitic composition that were metamorphosed under high-pressure low-temperature conditions. Slices of mainly Cretaceous clastic sedimentary rocks within the suture zone are interpreted as a deformed forearc basin that bordered the Eurasian active margin. The basin received a copious supply of sediments derived from Late Cretaceous arc volcanism together with input of ophiolitic detritus from accreted oceanic crust. Accretionary melange was emplaced southwards onto the leading edge of the Tauride continent (Munzur Massif) during latest Cretaceous time. Accretionary melange was also emplaced northwards over the collapsed southern edge of the Eurasian continental margin (continental backstop) during the latest Cretaceous. Sedimentation persisted into the Early Eocene in more northerly areas of the Eurasian margin. Collision of the Tauride and Eurasian continents took place progressively during latest Late Palaeocene–Early Eocene. The Jurassic SSZ ophiolites and the Cretaceous accretionary melange finally docked with the Eurasian margin. Coarse clastic sediments were shed from the uplifted Eurasian margin and infilled a narrow peripheral basin. Gravity flows accumulated in thrust-top piggyback basins above accretionary melange and dismembered ophiolites and also in a post-collisional peripheral basin above Eurasian crust. Thickening of the accretionary wedge triggered large-scale out-ofsequence thrusting and re-thrusting of continental margin and ophiolitic units. Collision culminated in detachment and northward thrusting on a regional scale. Collisional deformation of the suture zone ended prior to the Mid-Eocene (~45 Ma) when the Eurasian margin was transgressed by non-marine and/or shallow-marine sediments. The foreland became volcanically active and subsided strongly during Mid-Eocene, possibly related to post-collisional slab rollback and/or delamination. The present structure and morphology of the suture zone was strongly influenced by several phases of mostly S-directed suture zone tightening (Late Eocene; pre-Pliocene), possible slab break-off and right-lateral strike-slip along the North Anatolian Transform Fault. In the wider regional context, a double subduction zone model is preferred, in which northward subduction was active during the Jurassic and Cretaceous, both within the Tethyan ocean and bordering the Eurasian continental margin.

Reconstructing Upper Cretaceous (Cenomanian) paleoenvironments in Armenia based on Radiolaria and benthic Foraminifera; implications for the geodynamic evolution of the Tethyan realm in the Lesser Caucasus

Article

Full-text available

Nov 2014
PALAEOGEOGR PALAEOCL

A New Starting Point for the History of the Central Atlantic

Article

Full-text available

May 2005

A new starting point for the history of the central Atlantic. The first oceanic crust in the central Atlantic is usually thought to have a Middle Jurassic age. The new interpretation of the two key parameters, the African homologue of the East Coast Magnetic Anomaly and the situation of the Triassic salt basin of Morocco and Novia Scotia, shows that this age was underestimated by about 20 Ma. In our kinematic reconstruction, the first oceanic crust begins at the Late Sinemurian. This difference in age is crucial for the evolution of those margins and we discuss here its consequences. La première croûte océanique de l'Atlantique central est le plus souvent attribuée au Jurassique moyen. Notre reconstruction la situe à la fin du Sinémurien, soit environ 20 Ma plus tôt, différence capitale pour la modélisation des marges américaine et africaine. Cette révision, qui met fin à nombre de contradictions, est fondée sur la réinterprétation de deux éléments clés : l'équivalent africain de la East Coast Magnetic Anomaly, d'une part, l'extension des bassins à évaporites triasico-liasiques du Maroc et de Nouvelle-Écosse, d'autre part. L'article est consacré à cette réinterprétation et à ses conséquences en termes d'âge.

Understanding DRM acquisition of plates and spheres: A first comparative experimental approach

Article

Full-text available

Jul 2013
GEOPHYS J INT

Dario Bilardello

Since King presented the ‘plates and spheres’ model in an attempt to investigate the origin of the inclination error in sediments, no one to date has conducted specific experiments designed to separate the individual contribution of platy and spherical particles to depositional remanent magnetizations (DRMs). It is commonly accepted that it is the flattening of plates, rather than the rolling of spheres that is the main source of inclination error in sediments. Recently, however, Bilardello et al. have shown that spheres alone may lead to significant amounts of shallowing. A comparison of experiments run in parallel using synthetic platy and spherical particles is presented. Experiments of the duration of 24 hr were run in 100 μT field intensity (μ0H) and varying field inclinations (IF) from vertical to horizontal. A systematic dependence of the magnetization on field inclination is apparent. Results indicate that magnetic moment measurements are more repeatable for spherical particles than for plates, yielding smaller uncertainties. Inclination measurements, however, are more repeatable for platy particles, with a more linear relationship of inclination error to applied field inclination. Moreover, plates yield smaller inclination error than spheres. A clear field inclination dependency of the inclination error also exists, with the error decreasing through field inclinations of 30°, 60° and 90°. A continuous acquisition experiment involving plates was also run up to 10 d of deposition in μ0H = 100 μT and IF = 60°. The acquisition curves for moment, inclination and thickness of depositing sediment are compared to the mean curves measured for spheres by Bilardello et al. under the same field conditions. No unequivocal evidence of compaction of the platy particles is observed, while the inclination error is acquired virtually instantaneously for all particles. These preliminary results contradict the widespread understanding that inclination shallowing is more prominent for platy particles (e.g. hematite) than it is for more spherical particles (e.g. magnetite). It is true that larger amounts of shallowing have been commonly observed in natural hematite-bearing rocks, but the overall ranges of shallowing are also larger. The particles used in these experiments may not be a reliable proxy for natural crystals and one must exercise caution when extrapolating to the natural scenarios; however, the results provide insight into the behaviour of differently shaped particles.

The tectonics of the Central Anatolian Crystalline Complex: a structural, metamorphic and paleomagnetic study (PhD thesis)

Article

Full-text available

Nov 2011

Côme Lefebvre

The Anatolian region is a segment of the Alpine-Himalayan orogen. The rocks presently exposed in Anatolia provide a geological record of the closure history of the Neotethyan Ocean(s) situated between the converging African and Eurasian continents during late Mesozoic – Cenozoic times. The location of the former northern Neo-Tethyan ocean is marked by the presence of an ophiolitic mélange forming the Izmir-Ankara-Erzincan Suture Zone (IAESZ). South of the IAESZ, the Central Anatolian Crystalline Complex (CACC), made up of metamorphic rocks, ophiolites and magmatic intrusions, is the largest metamorphic domain exposed in Turkey. This crystalline domain experienced a complex tectonic history involving late Cretaceous obduction of ophiolitic nappes onto Paleozoic-Mesozoic sedimentary units, development of a regional Barrovian metamorphism and widespread magmatic intrusions. However, previous metamorphic, magmatic and structural studies in central Anatolia did not reach a consensus about a geodynamic scenario to explain the setting in which the CACC evolved during the late Cretaceous. This thesis provides a multi-scale and multi-disciplinary study of the tectono-metamorphic evolution of the CACC, and integrates the obtained results with data from the literature in order to propose a plausible tectonic model for the evolution of the CACC in the late Cretaceous.The tectono-metamorphic history of the central Anatolian metamorphic rocks has been investigated through detailed microstructural, metamorphic and geochronological analysis, together with local and regional mapping of ductile structures and metamorphic field gradients. An extended set of paleomagnetic data from the central Anatolian granitoids provides constraints allowing to restore the large-scale geometry of the CACC to its late Cretaceous configuration. The main results of this thesis can be summarized as follows. It is shown that during the late Cretaceous the CACC consisted of a NNE-SSW elongated and narrow dome-shaped antiformal structure (~500x150km). In this configuration, regional Barrovian metamorphism was accompanied with a top-to-the-SSW ductile crustal flow active in the deeper part of the antiform, while shallower levels were synchronously affected by WNW-ESE directed exhumation. Post-tectonic magmatism affected the western side of the antiform and involved three successive magmatic events showing a chemical evolution from calc-alkaline in the west to alkaline in the east (i.e. from an external to a more internal position in the antiform).This magmatic trend, together with published geochemical data from the central Anatolian plutonic rocks, has been recognized as a typical evolution associated with a supra-subduction environment of a magmatic arc. Therefore, the contemporaneous L/MP-HT arc metamorphism of the CACC together with the subduction-related HP-LT Tavşanlı Zone most likely formed a paired metamorphic belt. Moreover, at the plate tectonic scale, the contemporaneous northward subduction below the Pontides along an EW-trending suture together with the newly established eastward subduction of a NNE-SSW trending subduction system below the CACC, suggests the presence of a Trench-Trench-Trench type (TTT) triple junction at the intersection of these two subduction zones. Finally, the collision of the NNE-SSW-oriented antiformal structure with the central Pontides led to the break-up of the CACC into three distinctive domains and the development of its present-day triangular geometry during the Paleogene.

A compaction correction for the paleomagnetism of the Nanaimo Group sedimentary rocks: Implications for the Baja British Columbia hypothesis

Article

Full-text available

Feb 2004

A paleomagnetic and magnetic anisotropy study of the Late Cretaceous Northumberland formation on Hornby Island, British Columbia, was conducted to determine if burial compaction could have caused its anomalously shallow inclinations. The shallow Nanaimo Group inclinations have been used to support the Baja British Columbia (Baja BC) model of continental dynamics in which superterranes were transported thousands of kilometers northward along the active North American continental margin in the Cretaceous. A mean of the site means from the Northumberland formation is D = 5.8°, I = 50.9°, α95 = 7.9° (N = 8). Anisotropy of magnetic susceptibility (AMS) and anisotropy of anhysteretic remanence (AAR) were measured to identify and correct for any inclination shallowing caused by depositional/compactional processes. Both concretion and fine-grained rock samples had typical depositional/compactional AMS and AAR fabrics with bedding perpendicular minimum principal axes. A revised correction equation was used to account for the effects of either triaxial magnetic fabrics or small angular deviations of principal axes from the bedding plane. The average inclination was increased by 9.6° after the compaction correction (D = 6.1°, I = 60.5°, α95 = 7.1°, N = 8), and the mean inclination of concretion and fine-grained rock sites was significantly steeper than Ward et al.'s [1997] result (I = 42.5°) placing Hornby Island and the Insular superterrane at a paleolatitude of 41°N in the Late Cretaceous. This paleolatitude indicates that Baja BC did translate northward since the Late Cretaceous by about 1600 km but not by the 3500 km previously indicated.

Magnetic anisotropy, scanning electron microscopy, and X ray pole figure goniometry study of inclination shallowing in a compacting clay-rich sediment

Article

Full-text available

Dec 1992

The interaction between magnetite and clay particles, which causes the inclination shallowing during compaction, was investigated by studying the anisotropy of anhysteretic remanence, scanning electron micrographs, and the X-ray pole figure goniometry data obtained for clay-rich sediments compacted by pressures as high as 0.157 MPa and the effect of the interaction between these data on the inclination shallowing. The SEM observations of compacting magnetite/clay sediments indicated the occurrence of the attachment of magnetite particles to clay particles, causing the inital lock-in of a postdepositional remanence (PDRM) or DRM in clay-rich sediments. It is one cause of compaction-caused inclination shallowing at burial depths greater than 200 m.

Eocene paleomagnetism of the Caucasus (southwest Georgia): Oroclinal bending in the Arabian syntaxis

Article

Full-text available

Feb 2002
TECTONOPHYSICS

The Caucasus is very important for our understanding of tectonic evolution of the Alpine belt, but only a few reliable paleomagnetic results were reported from this region so far. We studied a collection of more than 300 samples of middle Eocene volcanics and volcano-sedimentary rocks from 10 localities in the Adjaro–Trialet tectonic zone (ATZ) in the western part of the Caucasus. Stepwise thermal demagnetization isolates a characteristic remanent magnetization (ChRM) in 19 sites out of 31 studied. ChRM reversed directions prevail, and a few vectors of normal polarity are antipodal to the reversed ones after tilt correction. The fold test is positive too, and we consider the ChRM primary. Analysis of Tertiary declinations and strikes of Alpine folds in the Adjaro–Trialet zone and the Pontides in Northern Turkey shows a large data scatter; Late Cretaceous data from the same region, however, reveal good correlation between paleomagnetic and structural data. Combining Late Cretaceous and Tertiary data indicates oroclinal bending of the Alpine structures which are locally complicated with different deformation. The overall mean Tertiary inclination is slightly shallower than the reference Eurasian inclination recalculated from one apparent polar wander path (APWP), but agrees with other. This finding is in accord with geological evidence on moderate post-Eocene shortening across the Caucasus. We did not find any indication of long-lived paleomagnetic anomalies, such as to Cenozoic anomalously shallow inclinations further to the east in Central Asia.

Van Hoof, A. A. M. & Langereis, C. G. Reversal records in marine marls and delayed acquisition of remanent magnetization. Nature 351, 223-225

Article

Full-text available

May 1991
NATURE

RECORDS of geomagnetic reversals 'frozen' into the magnetic components of sediments provide a means to study the time-dependent behaviour of the geomagnetic field during polarity transitions. Although sedimentary records have the advantage of being readily available and continuous, the process by which they acquire a remanent magnetization is still not fully understood1. Magnetites, which lose their magnetization at relatively high temperatures (<~580 °C), are generally considered to carry the primary remanence of the sediment—that is, to record the palaeomagnetic direction. Here we describe two reversed-to-normal transitional records from marine marls in which this high-temperature component shows a delayed remanence acquisition relative to a lower-temperature component. In these samples, therefore, the high-temperature component does not reflect geo-magnetic changes during the reversal. At least for marine marls, detailed palaeomagnetic, rock-magnetic and geochemical studies are apparently necessary to judge the validity of reversal records.

Un nouveau point de d??part pour l'histoire de L'Atlantique central

Article

Full-text available

Sep 2004
CR GEOSCI

The first oceanic crust in the central Atlantic is usually thought to have a Middle Jurassic age. The new interpretation of the two key parameters, the African homologue of the East Coast Magnetic Anomaly and the situation of the Triassic salt basin of Morocco and Novia Scotia, shows that this age was underestimated by about 20 Ma. In our kinematic reconstruction, the first oceanic crust begins at the Late Sinemurian. This difference in age is crucial for the evolution of those margins and we discuss here its consequences. To cite this article: M. Sahabi et al., C. R. Geoscience 336 (2004).

Tethyan evolution of Turkey: A plate tectonic approach

Article

Full-text available

Jun 1981
TECTONOPHYSICS

The Tethyan evolution of Turkey may be divided into two main phases, namely a Palaeo-Tethyan and a Neo-Tethyan, although they partly overlap in time. The Palaeo-Tethyan evolution was governed by the main south-dipping (present geographic orientation) subduction zone of Palaeo-Tethys beneath northern Turkey during the Permo-Liassic interval. During the Permian the entire present area of Turkey constituted a part of the northern margin of Gondwana-Land. A marginal basin opened above the subduction zone and disrupted this margin during the early Triassic. In this paper it is called the Karakaya marginal sea, which was already closed by earliest Jurassic times because early Jurassic sediments unconformably overlie its deformed lithologies. The present eastern Mediterranean and its easterly continuation into the Bitlis and Zagros oceans began opening mainly during the Carnian—Norian interval. This opening marked the birth of Neo-Tethys behind the Cimmerian continent which, at that time, started to separate from northern Gondwana-Land. During the early Jurassic the Cimmerian continent internally disintegrated behind the Palaeo-Tethyan arc constituting its northern margin and gave birth to the northern branch of Neo-Tethys. The northern branch of Neo-Tethys included the Intra-Pontide, Izmir—Ankara, and the Inner Tauride oceans. With the closure of Palaeo-Tethys during the medial Jurassic only two oceanic areas were left in Turkey: the multi-armed northern and the relatively simpler southern branches of Neo-Tethys. The northern branch separated the Anatolide—Tauride platform with its long appendage, the Bitlis—Pötürge fragment from Eurasia, whereas the southern one separated them from the main body of Gondwana-Land. The Intra-Pontide and the Izmir—Ankara oceans isolated a small Sakarya continent within the northern branch, which may represent an easterly continuation of the Paikon Ridge of the Vardar Zone in Macedonia. The Anatolide-Tauride platform itself constituted the easterly continuation of the Apulian platform that had remained attached to Africa through Sicily. The Neo-Tethyan oceans reached their maximum size during the early Cretaceous in Turkey and their contraction began during the early late Cretaceous. Both oceans were eliminated mainly by north-dipping subduction, beneath the Eurasian, Sakaryan, and the Anatolide- Tauride margins. Subduction beneath the Eurasian margin formed a marginal basin, the present Black Sea and its westerly prolongation into the Srednogorie province of the Balkanides, during the medial to late Cretaceous. This resulted in the isolation of a Rhodope—Pontide fragment (essentially an island arc) south of the southern margin of Eurasia. Late Cretaceous is also a time of widespread ophiolite obduction in Turkey, when the Bozkir ophiolite nappe was obducted onto the northern margin of the Anatolide—Tauride platform. Two other ophiolite nappes were emplaced onto the Bitlis—Pötürge fragment and onto the northern margin of the Arabian platform respectively. This last event occurred as a result of the collision of the Bitlis—Pötürge fragment with Arabia. Shortly after this collision during the Campanian—Maastrichtian, a subduction zone began consuming the floor of the Inner Tauride ocean just to the north of the Bitlis—Pötürge fragment producing the arc lithologies of the Yüksekova complex. During the Maastrichtian—Middle Eocene interval a marginal basin complex, the Maden and the Çüngüş basins began opening above this subduction zone, disrupting the ophiolite-laden Bitlis—Pötürge fragment. The Anatolide-Tauride platform collided with the Pontide arc system (Rhodope—Pontide fragment plus the Sakarya continent that collided with the former during the latest Cretaceous along the Intra Pontide suture) during the early to late Eocene interval. This collision resulted in the large-scale south-vergent internal imbrication of the platform that produced the far travelled nappe systems of the Taurides, and buried beneath these, the metamorphic axis of Anatolia, the Anatolides. The Maden basin closed during the early late Eocene by north-dipping subduction, synthetic to the Inner-Tauride subduction zone that had switched from south-dipping subduction beneath the Bitlis—Pötürge fragment to north dipping subduction beneath the Anatolide—Tauride platform during the later Palaeocene. Finally, the terminal collision of Arabia with Eurasia in eastern Turkey eliminated the Çüngüş basin as well and created the present tectonic regime of Turkey by pushing a considerable piece of it eastwards along the two newly-generated transform faults, namely those of North and East Anatolia. Much of the present eastern Anatolia is underlain by an extensive mélange prism that accumulated during the late Cretaceous—late Eocene interval north and east of the Bitlis—Pötürge fragment.

Prolonged Variscan to Alpine history of an active Eurasian margin (Georgia, Armenia) revealed by 40Ar/39Ar dating

Article

Full-text available

Nov 2011
GONDWANA RES

Variscan to Alpine magmatic activity on the North Tethys active Eurasian margin in the Caucasus region is revealed by 40Ar/39Ar ages from rocks sampled in the Georgian Crystalline basement and exotic blocs in the Armenian foreland basin. These ages provide insights into the long duration of magmatic activity and related metamorphic history of the margin, with: (1) a phase of transpression with little crustal thickening during the Variscan cycle, evidenced by HT-LP metamorphism at 329–337Ma; (2) a phase of intense bimodal magmatism at the end of the Variscan cycle, between 303 and 269Ma, which is interpreted as an ongoing active margin during this period; (3) further evolution of the active margin evidenced by migmatites formed at ca. 183Ma in a transpressive setting; (4) paroxysmal arc plutonic activity during the Jurassic (although the active magmatic arc was located farther south than the studied crystalline basements) with metamorphic rocks of the Eurasian basement sampled in the Armenian foreland basin dated at 166Ma; (5) rapid cooling suggested by similar within-error ages of amphibole and muscovite sampled from the same exotic block in the Armenian fore-arc basin, ascribed to rapid exhumation related to extensional tectonics in the arc; and finally (6) cessation of ‘Andean’-type magmatic arc history in the Upper Cretaceous. Remnants of magmatic activity in the Early Cretaceous are found in the Georgian crystalline basement at c. 114Ma, which is ascribed to flat slab subduction of relatively hot oceanic crust. This event corresponds to the emplacement of an oceanic seamount above the N Armenian ophiolite at 117Ma. The activity of a hot spot between the active Eurasian margin and the South Armenian Block is thought to have heated and thickened the Neo-Tethys oceanic crust. Finally, the South Eurasian margin was uplifted and transported over this hot oceanic crust, resulting in the cessation of subduction and the erosion of the southern edge of the margin in Upper Cretaceous times. Emplacement of Eocene volcanics stitches all main collisional structures.

Regional and petroleum geology of the black sea and surrounding region

Article

Jan 1997

Geologic Time Scale

Chapter

Jan 2016

Felix Gradstein

The geologic time scale (GTS) provides the framework for the physical, chemical, and biological processes in time on Earth. The most up-to-date GTS is available since October 2012. Geoscientists can easily create and print time scale charts, utilizing the freely available software package “Time Scale Creator @.”.

The Cretaceous Period

Chapter

Mar 2005

The Pangea supercontinent fractures into the modern drifting continents. An explosion of calcareous nannoplankton and foraminifera in the warm seas creates massive chalk deposits. A surge in undersea volcanic activity and spreading-ridge formation enhances super-greenhouse conditions in the middle—Late Cretaceous. Angiosperm plants bloom on the dinosaur-dominated land during the Late Cretaceous. The Cretaceous dramatically ends with an asteroid impact. HISTORY AND SUBDIVISIONS Overview of the Cretaceous Chalk (creta in Latin) characterizes a major unit of strata around the Paris Basin and extends across much of Europe. The “Terrain Crétacé” was established by d'Omalius d'Halloy (1822) and defined by him in 1823 to include “the formation of the chalk, with its tufas, its sands and its clays.” William Smith had already mapped four stratigraphic units between the “lower clay” (Eocene) and “Portland Stone” (Jurassic), which were grouped by Conybeare and Phillips (1822) into two divisions: the Chalk and the formations below.

Geology of the eastern pontides

Article

Jan 1997

The 500-km-long Eastern Pontide belt shows several common stratigraphie features resulting from a common Mesozoic-Tertiary tectonic history. There is a heterogeneous pre-Jurassic basement comprised of Devonian? high-grade metamorphic rocks, Lower Carboniferous granodiorites and dacites, Upper Carboniferous-Lower Permian shallow-marine to terrigeneous sedimentary rocks and an allochthonous Permo-Triassic metabasite-phyllite-marble unit. The Mesozoic sedimentary sequence starts with a widespread Liassic marine transgression coming from the south. The Lower and Middle Jurassic rocks of the Eastern Pontides make up a 2000-m-thick sequence of tuff, pyroclastic rock, lava, and interbedded clastic sedimentary rock; the volcanism is probably related to rifting leading to the opening of the Neotethyan Ocean in the south. The Upper Jurassic-Lower Cretaceous is characterized by carbonates, showing a transition from platform carbonate deposition in the north to pelagic carbonates and calciturbidites in the south; this indicates the development of a south-facing passive continental margin. During the Cenomanian, there was uplift and erosion throughout the Eastern Pontides. Rocks of this stage are not present, and in many localities the Senonian deposits lie unconformably over Jurassic carbonates and even over the Carboniferous granitic basement. This compressive event is associated with the northward emplacement of an ophiolitic melange over the passive continental margin of the Eastern Pontides. The obduction of the ophiolitic melange is probably caused by the partial subduction of the Eastern Pontides continental margin in a south-dipping intra-oceanic subduction zone. This was followed by the flip of the subduction polarity during the Cenomanian-Turonian, which led to the development of a Senonian volcanic arc in the outer Eastern Pontides above the northward-subducting Tethyan Ocean floor. The volcanic arc is represented by >2-km-thick succession of volcanic and volcaniclastic rocks and interbedded limestones and marls. There are also intrusive granodiorite plutons with isotopic ages of 95 to 65 m.y. The volcanism shows a general silica enrichment, with time, ranging from basalts and andésites to dacites. The Senonian sequence in the inner Eastern Pontides is made up of a tuffaceous flyschoid series representing the fore-arc succession. The Eastern Black Sea Basin probably opened during the Maastrichtian through the rifting of the volcanic arc axis. During the late Paleocene-early Eocene, there was north-vergent thrust imbrication of the inner Eastern Pontides with the development of a major foreland flysch basin in front of the northward moving thrust sheets. Folding and uplift occurred in the outer Eastern Pontides during this period. This compressive deformational event, the strongest Mesozoic-Tertiary orogenic phase in the Eastern Pontides, was probably caused by the collision between the Pontide arc and the Tauride microplate in the south. Widespread calc-alkaline volcanism and shallow-marine sedimentation occurred throughout the Eastern Pontides during the middle Eocene. The middle Eocene rocks are essentially undeformed and lie unconformably over a folded and thrust-faulted basement. This major middle Eocene extensional event is probably related to an accelarated phase of opening of the Eastern Black Sea Basin. From the end of the middle Eocene onward, the Eastern Pontides stayed largely above sea level, with minor volcanism and terrigeneous sedimentation.

Prealpine basement of the Caucasus - composition, structure, and formation

Article

Jan 1984

Shota Adamia

Palaeomagnetism of Upper Cretaceous Rocks from the Caucasus and its Implications for Tectonics

Chapter

Jan 1989

The Caucasus region was subdivided into two domains according to their Alpine structural patterns. The WNW trends prevail within the northern domain (the Great Caucasus), and fold axes outline a large arc within the southern one (the Lesser Caucasus). Sedimentary rocks of Late Cretaceous age have been sampled in Dagestan near the northern margin of the Great Caucasus, and on both flanks of the Lesser Caucasus arc. Directions of a prefolding, most probably primary, component of natural remanent magnetization have been obtained after treatments in the laboratory. The Upper Cretaceous limestones from Dageston yielded a mean paleopole at 74°N and 151°E, closely matching the Cretaceous-Palaeogene part of the Eurasian polar wander path. Declinations ranging from 353° to 37° correspond to changes of fold axis trends within the Lesser Caucasus thus pointing to tectonic origin of the arc. The inclinations for the northern and southern domains differ by 8°+3° We conclude that the Lesser Caucasus moved about 900+350 kilometers northward with respect to stable Eurasia since Late Cretaceous.

The Alpine Middle East between the Aegean and the Oman traverses

Article

Jan 1980

The Paleozoic-Mesozoic

Article

Jan 1964

R.A. Arakelyan

Relicts of Mesozoic oceanic crust among the crystalline complexes of the Miskhana massif of Armenia

Article

Jan 1973

New data on the age of Vedi ophiolite (Armenia)

Article

Apr 1994

New information on the age of ophiolites in the Vedi area appeared including those that were obtained in the summer of 1989 on the left bank of the Kyusuz River in the Vedi River basin. The collected siliceous rock samples contained radiolarian remains. The three-dimensional radiolarians identified show the Late Jurassic-Early Cretaceous age of the Khosrov volcanogenic-siliceous series.

Discontinuation on the boundary between Middle and Upper Permian in Armenia (Abstract)

Article

Jan 2012

The Paleogene Period

Article

Mar 2005

After the global Cretaceous–Paleogene boundary impact catastrophy, planktonic foraminifera and nannofossils start new evolutionary trends, and mammals appear on Earth; global warming episode occurs at the Paleocene–Eocene boundary and significant cooling trends develop in later Paleogene in preparation for Modern life and climate. Orbital tuning of deep-marine cyclic sedimentation patterns, calibrated to the geomagnetic polarity and biostratigraphic scales, have the potential to elevate the Paleogene time scale to the level of resolution of the Neogene. HISTORY AND SUBDIVISIONS Overview of the Paleogene The Cenozoic Era (Phillips, 1841, originally “Cainozoic,” from kainos = new and zoon = animal) is subdivided into the Paleogene (palaios = old, genos = birth) and Neogene periods. The use of “Tertiary” (Arduino, 1759) and “Quaternary” (Desnoyers, 1829) is not recommended, being equally antiquated terms such as Primary and Secondary that have fallen into disuse in the twentieth century. Naumann (1866) combined in his “Paleogen Stufe,” the Eocene and Oligocene, as opposed to the “Neogen Stufe” of Hörnes (1853) which included not only the miocene and the Pliocene, but also fauna of the Pleistocene (see Chapter 21).

Flood basalts and hotspot tracks: plume heads and tails

Article

Jan 1989

The least-squares line and plane and analysis of paleomagnetic data

Article

Jan 1980

J.L. Kirschvink

Structural position of ophiolites of the Caucasus.

Article

Jan 1980
OFIOLITI

Two major ophiolite zones occur in Caucasus. The northern Front Range ophiolite in Great Caucasus constitutes a sliced unit as a complex of four major nappes; it includes serpentinized harzburgites, gabbro-norites, diabases, basaltic porphyries and aphyries, with sedimentary slices. Ophiolites are of pre-Silurian age, and are interpreted as the crust of a marginal sea obducted on island arc sequences at the beginning of early Carboniferous. The southern ophiolite belt in Lesser Caucasus includes ultramafics, gabbros, spilites and radiolarian cherts. The Vedi Zone comprises, from bottom to top: the autochthon ending in Lower Coniacian; an ophiolite-bearing melange nappe; an ultramafic-gabbro nappe. The Sevan-Akera zone displays an autochthon topped by Lower Coniacian and a sequence of nappes including, from bottom to top, ultramafics and gabbros, Upper Jurassic-Lower Cretaceous volcano-sedimentary sequences, Cenomanian olistostromes and basalts, and serpentinite melange. In both zones Neo-authochton begins in Upper Coniacian. The Lesser Caucasus ophiolites represent a Mesozoic oceanic crust obducted both N (Sevan-Akera) and S (Vedi) from a suture line (Zangezur), as a consequence of the collision of the African and European plates since Cenomanian. -from Authors

Petrology, geochemistry, and Sm-Nd age of the pre-Late Hercynian paleooceanic complex of the Dzirula salient, Transcaucasian Massif

Article

Jul 1998
PETROLOGY+

Metaophiolites were examined in the tectonic melange of the Chorchana-Utslevi zone, along with the accompanying calc-alkalinegabbroids, diorites, quartz diorites, and metasediments of the pre-Late Hercynian complex in the crystalline basement of the Dzirula salient, Transcaucasian Massif. The metaophiolites correspond to fragments of the paleooceanic lithosphere of the spreading-zone type. The ultramafic constituents are clinopyroxene-bearing spinel harzburgite of the oceanic type, which is restite after extraction of tholeiite basalts. The protolith of the metabasics (amphibolites and epidote amphibolites T=500-450°C, P=4-3.5 kbar) compositionally approximated tholeiites of the N- and T-MORB types. The whole rock Sm-Nd isotopic dat of the metabasites correspond to an age of T=810±100Ma, εNdinit = 7.37±0.55. The pre-Late Hercynian gneiss-migmatite complex underwent extensive metamorphism and palingenesis under amphibolite-facies conditions. The process was accompanied by the emplacement of numerous subvolcanic mafic intrusions of the calc-alkaline series. The youngest calc-alkaline gabbroids have the following isotopic-geochemical characteristics: T= 607±78 Ma, εNdinit = 1.2, (La/Sm)n = 2.30±0.60, (Yb)MORB = 0.48±0.17. The palingenetic diorite and quartz diorite of the gneiss-migmatite complex show strong geochemical similarities with the gabbroids. The gneiss-migmatite complex was dated at the Late Proterozoic and identified as a type of primitive (immature) continental crust. The rock association examined in the Transcaucasian Massif was produced during the Pan-African (Baikalian) tectonic cycle, with the massif itself being the northern periphery of the Arabian-Nubian Shield in Late Proterozoic time. The metasediments from in the tectonic melange of the Chorchana-Utslevi zone originated during the early stages of development of the northern Phanerozoic passive margin of Gondwana. Copyright © 1998 by MAEe Cyrillic signK Hayκa/Interperiodica Publishing.

Paleomagnetism of Sedimentary Rocks: Process and Interpretation

Book

Aug 2012

Kenneth P. Kodama

This book describes the paleomagnetism of sediments and sedimentary rocks, how sediments and sedimentary rocks become magnetized, and how the physical and chemical processes involved can affect the accuracy of paleomagnetism. Topics covered include depositional and post-depositional remanence acquisition, the detection and correction of compaction-caused inclination shallowing, reduction diagenesis of magnetic minerals, chemical remagnetization, and rotation of remanence by grain-scale rock strain. The book also has a chapter on environmental paleomagnetism, including examples of the new technique of high-resolution rock magnetic cyclostratigraphy and its application to sedimentary sequences. By emphasising the accuracy of sedimentary paleomagnetism and the magnitude of post-depositional processes that can affect it, the book will be invaluable in the geologic interpretation of sedimentary paleomagnetic data. Paleomagnetism of Sedimentary Rocks will be welcomed by paleomagnetists, students of paleomagnetism and all Earth scientists who use sedimentary paleomagnetic data in their research.

Multi-stage metamorphism in the South Armenian Block during the Late Jurassic to Early Cretaceous: Tectonics over south-dipping subduction of Northern branch of Neotethys

Article

Apr 2015
J ASIAN EARTH SCI

A Simplified Statistical Model for the Geomagnetic Field and the Detection of Shallow Bias in Paleomagnetic Inclinations: Was the Ancient Magnetic Field Dipolar?

Article

Jan 2004

The assumption that the time-averaged geomagnetic field closely approximates that of a geocentric axial dipole (GAD) is valid for at least the last 5 million years and most paleomagnetic studies make this implicit assumption. Inclination anomalies observed in several recent studies have called the essential GAD nature of the ancient geomagnetic field into question, calling on large (up to 20%) contributions of the axial octupolar term to the geocentric axial dipole in the spherical harmonic expansion to explain shallow inclinations for even the Miocene. In this paper, we develop a simplified statistical model for paleosecular variation (PSV) of the geo magnetic field that can be used to predict paleomagnetic observables. The model pre dicts that virtual geomagnetic pole (VGP) distributions are circularly symmetric, implying that the associated directions are not, particularly at lower latitudes. Elon gation of directions is North-South and varies smoothly as a function of latitude (and inclination). We use the model to characterize distributions expected from PSV to distinguish between directional anomalies resulting from sedimentary incli nation error and from non-zero non-dipole terms, in particular a persistent axial octupole term. We develop methodologies to correct the shallow bias resulting from sedimentary inclination error. Application to a study of Oligo-Miocene redbeds in central Asia confirms that the reported discrepancies from a GAD field in this region are most probably due to sedimentary inclination error rather than a non-GAD field geometry or undetected crustal shortening. Although non-GAD fields can be imagined that explain the data equally well, the principle of least astonishment requires us to consider plausible mechanisms such as sedimentary inclination error as the cause of persistent shallow bias before resorting to the very "expensive" option of throwing out the GAD hypothesis.

Global Hotspot Reference Frames and Plate Motion

Article

Jan 2000

Ian O. Norton

Most of the earth's new magmatic material is produced at volcanic centers associated with plate boundary processes. These are either arc volcanoes above subduction zones or linear spreading centers along divergent plate boundaries. Scattered about Earth's surface, however, are many volcanic centers that are not associated with plate boundary processes. These are usually found far from plate boundaries, and they continue to produce magma from a well-defined central location for many tens of millions of years. Geochemical studies of the products of these volcanic centers shows that their magma comes from deep within the mantle, below the tectonic plates that form the top 100 km of the earth. The term `hotspot' has been coined to describe these volcanic features. If the tectonic plate on which the volcanic center is located moves relative to the underlying magma source, a trail of volcanic features can be produced on the plate, a `hotspot track'. Probably the best-known example is associated with the island of Hawaii, with the Hawaii-Emperor seamount chain in the northern Pacific Ocean forming the `track'. An extension of the hotspot concept is the proposal that all the global hotspots stay fixed relative to one another and thus provide a complete reference frame in which to describe plate motion. This would be incredibly useful, as no other reference frame exists in which to describe absolute plate motion through time. The hotspot reference frame was thought to provide this, and many published studies of plate motion make use of this reference frame. As studies of plate motions have advanced, however, it has become clear that the global hotspots do not stay fixed relative to each other. In this paper it is proposed that there are three global families of hotspots, a Pacific family, an Indo-Atlantic family and also Iceland, a major hotspot in terms of volcanic material but not fixed to the other two families. Hotspots within each of the first two families have remained relatively fixed for the past 80 million years.

Inclination shallowing in deep sea sediments from the North Atlantic

Article

Jan 1988

Paleomagnetic data from Miocene to Recent deep sea sediments recovered during Leg 94 of the Deep Sea Drilling Project (DSDP) in the North Atlantic exhibit a systematic shallowing of inclinations with depth at some sites. This shallowing is coincident with a downhole decrease in water content, and is observed only in sediments with a carbonate content consistently greater than 80%. Compaction due to overburden pressure is believed to be responsible for the shallow inclinations observed in these unconsolidated sediments. At sites where the carbonate content of the sediments is consistently below about 80% no significant downcore decreasing trends in the water content or inclination record are observed.

Continent and Ocean Basin Evolution by Spreading of the Sea Floor

Article

Jun 1961
NATURE

Robert S. Dietz

Jurassic-Cretaceous paleomagnetism and paleogeography of the Pontides (Turkey)

Article

Feb 1996

Published paleomagnetic data from the Pontides indicate anomalously low Jurassic and Early Cretaceous paleolatitudes compatible with the southern Neo-Tethyan (African) continental margin and significantly different from paleolatitudes predicted for the northern (Eurasian) Neo-Tethyan margin. We present a new set of paleomagnetic data from 50 Late Cretaceous sites mainly from the Western Pontides and from the Eastern Pontides, and 11 Early Jurassic sites mainly from the Eastern Pontides. Fold tests indicate that the characteristic magnetization components predate Eocene folding. Late Cretaceous site mean declinations are northerly in the Eastern Pontides and rotated to the west by a few tens of degrees in the Western Pontides. Late Cretaceous site mean declinations are affected by local clockwise rotation in one sampling region close to the North Anatolian Fault. The mean Late Cretaceous inclinations and resulting paleolatitudes are 41.1° (23.5°N) and 43.7° (25.5°N) for the Western and Eastern Pontides, respectively. For the Eastern Pontides, the Early Jurassic (Liassic) mean inclination is 60.5°, yielding a paleolatitude of 41.4°N, considerably further north than previous paleolatitude estimates for the Eastern Pontides at this time. The paleolatitude estimates for the Western and Eastern Pontides are consistent with these units being close to the Eurasian continental margin during Liassic and Late Cretaceous time.

The Rift in the Ocean Floor

Article

Oct 1960

Bruce C. Heezen

Tethyan Sutures of northern Turkey

Article

Oct 1999

The two main Tethyan sutures of Turkey, the İzmir-Ankara-Erzincan and the Intra-Pontide sutures, are reviewed through several well-studied transects crossing the suture regions. Both sutures have formed during the Early Tertiary continental collisions following northward subduction of Tethyan oceanic lithosphere. The İzmir-Ankara-Erzincan suture is represented along most of its c. 2000 km length by Paleocene and younger thrust, which emplace the upper crustal rocks of the northern continent over that of the southern continent with an intervening tectonic layer of Cretaceous subduction-accretion complexes. These thrusts constitutes a profound stratigraphic, structural, magmatic and metamorphic break, of at least Carboniferous to Palaeocene age and form the main boundary between Laurasia and Gondwana in the Turkish transect. Voluminous subduction-accretion complexes of Triassic and Cretaceous ages occur respectively to the north and south of the suture giving the antithetic subduction polarities during these two periods. This, and evidence for a major accretionary orogeny of Late Triassic age north of the İzmir-Ankara-Erzincan suture suggest that two separate oceanic lithospheres, of Carboniferous to Triassic (Palaeo-Tethys) and of Triassic to Cretaceous ages (Neo-Tethys) respectively have been consumed along the suture. The final continental collision along the İzmir-Ankara-Erzincan suture was slightly diachronous and occurred in the earliest Palaeocene to the west and in the Late Palaeocene to the east. The c. 800 km long Intra-Pontide suture is younger in age and have formed during the Early Eocene and younger continental collisions linked to the opening of the Western Black Sea Basin as an oceanic back-arc basin. At present the North Anatolian Fault, which came into existence in the Late Miocene, follows the course of the older Intra-Pontide suture.

Stratigraphic and structural development of the Eastern Pontides, Turkey

Article

Oct 1995

The Eastern Pontides comprise a Late Carboniferous to Miocene sequence resting on a basement of Hercynian metamorphics. Late Carboniferous to Scythian sediments are continental clastics deposited in an extensional half graben. All pre-Aalenian strata were deformed during the Cimmerian orogeny. After a phase of subduction-related volcanism in the Mid-Jurassic, limestones were deposited during the Late Jurassic and early Cretaceous. There is a thick sequence of Upper Cretaceous arc volcanic rocks and intervening turbidites. The Upper Palaeocene is absent, possibly due to rifting in the Eastern Black Sea. Major compression affected the Pontides from the Eocene to the Pliocene -from Authors

Laboratory depositional and compaction-caused inclination errors carried by haematite and their implications in identifying inclination error of natural remanence in red beds

Article

Nov 2002
GEOPHYS J INT

Undetected depositional and/or compaction-caused inclination errors may result in an overestimation of tectonically caused latitudinal offset. Hodych & Buchan used a single-component isothermal remanent magnetization (IRM) acquired in a DC field at a 45° angle to the bedding to test for inclination errors in Silurian red beds. This approach was criticized by Stamatakos et al. We produced synthetic depositional and compaction-caused inclination errors to test Hodych and Buchan's approach. Red bed samples collected from the Eocene Suweiyi Formation, Tarim Basin (northwest China) were disaggregated using an ultrasonic cleaner and the sediments were mixed with distilled water to make a sediment slurry. The sediment slurry spontaneously separated into silt-dominated and clay-sized parts, so deposition and compaction experiments were conducted with three categories of slurries: coarse grained, the fine grained and a 1:1 volume ratio mixture of the coarse- and fine-grained slurries. During compaction clay-sized sediments experienced 17°-19° inclination shallowing at 58° magnetic field inclination, while coarser sediments showed little laboratory compaction-caused inclination error. Acquisition of IRM, coercivity spectra and unblocking temperature spectra reveal that the magnetic carrier for the fine-grained sample is dominated by pigmentary haematite. A deposition experiment was also conducted with the coarse-grained sediments, which showed a range of depositional inclination error, ~0°-30°, carried by larger high unblocking temperature/coercivity particles. The intermediate unblocking temperature (or coercivity) component carried presumably by pigmentary haematite is an accurate record of the ambient magnetic field direction. Our data indicate that the single-component IRM method of Hodych & Buchan can be used to identify and correct for the compaction-caused inclination error of the fine-grained samples, while it failed to detect any depositional inclination error in the coarse-grained samples. Therefore, to better quantify the inclination error in red beds, it is suggested that multiple IRMs be measured in various directions.

Can remanence anisotropy detect paleomagnetic inclination shallowing due to compaction? A case study using Cretaceous Deep-Sea limestones

Article

Dec 1993

We studied 35 Cretaceous limestone specimens from five Pacific plate Deep Sea Drilling Project sites. Inclination I(sub N) of the natural remanence is on average 17 deg shallower than the average 44 deg expected paleofied inclination I. Anhysteretic remanence (ARM) applied identically to various axes was found to be weakest (ARM(sub min)) perpendicular to bedding and strongest (ARM(sub max)) parallel to bedding. The average ARM(sub min)/ARM(sub max) of 0.87 as well as the inclination shallowing of 17 deg likely originated from sediment compaction rotating the long axes of magnetite grains toward the bedding plane. This origin is theoretically and experimentally consistent with the average fractional compaction of 0.6 experienced by our sediments (estimated from their porosity). A compaction origin is also supported by the significant correlation found between tan I(sub N)/tan I and ARM(sub min)/ARM(sub max). The correlation line's slope of 2.3 +/- 0.7 agrees with theory, taking into account our observation that ARM given perpendicular to the long axes of magnetite grains has on average approximately 0.37 times the intensity of ARM given axially. These results suggest that compaction-induced inclination shallowing may be detected in a suite of fine-grained magnetite-bearing sediments by looking for a correlation between tan I(sub N) and ARM(sub min)/ARM(sub max) (having shown that ARM(sub min)/ARM(sub max) = 1 should estimate I corrected for inclination shallowing.

Lower and Middle Jurassic paleomagnetic results from the south Lesser Caucasus and the evolution of the Mesozoic Tethys ocean

Article

Jun 1996
EARTH PLANET SC LETT

We studied Lower Jurassic (Pliensbachian-Toarcian) basalts and tuffs and Middle Jurassic (Bajocian) limestones and marls from 9 sites in the southern part of the Lesser Caucasus (ca. 39.3°N, 45.4°E). A component showing rectilinear decay to the origin was reliably isolated from most volcanics. This characteristic component reveals nearly antipodal directions for both polarities and passes the fold test; the conglomerate test performed on lava boulders from the Aalenian basal conglomerates is also positive. We think that a primary remanence (D = 20°, I = 38° a95 = 5°) was isolated from the volcanics. In contrast, Middle Jurassic sediments yielded controversial results, and the only reliably isolated intermediate-temperature component (ITC) does not pass the fold test. The ITC directions show a considerable improvement in data grouping during incremental unfolding, with a maximum at 40% unfolding. We argue, however, that the thus obtained mean direction does not correspond to any paleofield and is most probably an artefact.When compared to reference data for the Eurasian and African plates, the Lower Jurassic mean inclination of 21°N ± 4° agrees well with the latter, thus implying that, in the Early Jurassic, the area studied belonged to Gondwana and was separated by the Tethys ocean from Eurasia, in agreement with paleontological data. We tried to locate the position of the boundary between the Eurasian and Gondwanian realms in the Caucasus region in the Early-Middle Jurassic; unfortunately, the available Jurassic paleomagnetic data from other tectonic units of the region did not reveal any clear pattern.

Reply to comment of R.C. Bailey on “The combined analysis of remagnetization circles and direct observations in paleomagnetism”

Article

Nov 1990
EARTH PLANET SC LETT

P.L. McFadden

Apparent and true polar wander and the geometry of the geomagnetic field over the last 200 Myr

Article

Nov 2002

We have constructed new apparent polar wander paths (APWPs) for major plates over the last 200 Myr. Updated kinematic models and selected paleomagnetic data allowed us to construct a master APWP. A persistent quadrupole moment on the order of 3% of the dipole over the last 200 Myr is suggested. Paleomagnetic and hot spot APW are compared, and a new determination of ``true polar wander'' (TPW) is derived. Under the hypothesis of fixed Atlantic and Indian hot spots, we confirm that TPW is episodic, with periods of (quasi) standstill alternating with periods of faster TPW (in the Cretaceous). The typical duration of these periods is on the order of a few tens of millions of years with wander rates during fast tracks on the order of 30 to 50 km/Myr. A total TPW of some 30° is suggested for the last 200 Myr. We find no convincing evidence for episodes of superfast TPW such as proposed recently by a number of authors. Comparison over the last 130 Myr of TPW deduced from hot spot tracks and paleomagnetic data in the Indo-Atlantic hemisphere with an independent determination for the Pacific plate supports the idea that, to first order, TPW is a truly global feature of Earth dynamics. Comparison with numerical modeling estimates of TPW shows that all current models still fail to some extent to account for the observed values of TPW velocity and for the succession of standstills and tracks which is observed.

New and revised Radiolarian biochronology for the sedimentary cover of ophiolites in the Lesser Caucasus (Armenia).

Article

Sep 2010

In order to improve our understanding of the palaeogeographic and geodynamic evolution of the Tethyan realms preserved in the Lesser Caucasus we here review the existing data for the sedimentary cover of ophiolites preserved in Armenia. Particular attention is given to those dated sedimentary rocks that are in direct genetic contact with ophiolitic lavas, as they provide constraints for submarine oceanic activity. The oldest available ages come from the Sevan-Akera suture zone that point to a Late Triassic oceanization. Data from both the Sevan and Vedi ophiolites provide evidence for Middle Jurassic (Bajocian) submarine activity, that continued until at least the Late Jurassic (Mid/Late Oxfordian to Late Kimmeridgian/Early Tithonian), as dated recently in Stepanavan and in this study for the Vedi ophiolite.

A paleolatitude reconstruction of the South Armenian Block (Lesser Caucasus) for the Late Cretaceous: Constraints on the Tethyan realm

Abstract

No full-text available

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