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![Tectonic discrimination diagram of igneous rocks [91] in the Greater Caucasus for limited suites of Cenozoic felsic volcanic and intrusive rocks for which trace element isotopic data are available [74,66,65,69]. Q-Quaternary, Plio.Pliocene, Mio.-Miocene. The majority of samples from all volcanic fields, with the exception of the Pyatigorsk suite, which lies north of the Greater Caucasus near the town of Mineralnye Vody, reveal a volcanic arc-type signature. This signature is common to rocks known to have been associated with modern or past subduction (e.g. the modern and ancestral Cascades; Oligocene magmatism in the Basin and Range, [27,21], but differs from non-arc magmatism (e.g. Yellowstone and the Snake River Plain, [21]. Such a signature suggests a subduction-related origin for much of the Miocene to Recent volcanism in the Greater Caucasus. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)](profile/Nathan-Niemi/publication/269391445/figure/fig3/AS:613971778367523@1523393687963/Tectonic-discrimination-diagram-of-igneous-rocks-91-in-the-Greater-Caucasus-for-limited.png)
Tectonic discrimination diagram of igneous rocks [91] in the Greater Caucasus for limited suites of Cenozoic felsic volcanic and intrusive rocks for which trace element isotopic data are available [74,66,65,69]. Q-Quaternary, Plio.Pliocene, Mio.-Miocene. The majority of samples from all volcanic fields, with the exception of the Pyatigorsk suite, which lies north of the Greater Caucasus near the town of Mineralnye Vody, reveal a volcanic arc-type signature. This signature is common to rocks known to have been associated with modern or past subduction (e.g. the modern and ancestral Cascades; Oligocene magmatism in the Basin and Range, [27,21], but differs from non-arc magmatism (e.g. Yellowstone and the Snake River Plain, [21]. Such a signature suggests a subduction-related origin for much of the Miocene to Recent volcanism in the Greater Caucasus. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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![Fig. 3. Tectonic discrimination diagram of igneous rocks [91] in the...](profile/Nathan-Niemi/publication/269391445/figure/fig3/AS:613971778367523@1523393687963/Tectonic-discrimination-diagram-of-igneous-rocks-91-in-the-Greater-Caucasus-for-limited_Q320.jpg)
The Greater Caucasus Mountains contain the highest peaks in Europe and define, for over 850 km along strike, the leading edge of the second-largest active collisional orogen on Earth. However, the mechanisms by which this range is being constructed remain disputed. Using a new database of earthquake records from local networks in Georgia, Russia, a...
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... the geochemistry of silicic lavas in the Greater Cauca- sus is consistent with genesis in a volcanic arc setting (Fig. 3), their geographic distribution is harder to explain (Fig. 4). Elbrus, Chegem and Kazbek define a trend along-strike within the Greater Cauca- sus consistent with a volcanic arc developed above a northeast- dipping subduction zone. However, the presence of late Miocene intrusions at Pyatigorsk and Lelaashka, significantly north and south, respectively, of this trend, is somewhat unusual. One possi- ble explanation for the spatial trend of volcanism is small-scale toroidal flow around the edge of the seismically observed slab (e.g., [119,55]) perhaps enhanced by small-scale convection gener- ated across a steep gradient in lithospheric thickness that underlies the Greater Caucasus (e.g., [59,78]). Nonetheless it remains unclear why volcanism appears absent east of $45 E, where both the earthquake locations presented in this work and elsewhere [80], along with modeling of GPS velocity data [110,94] indicate active subduction. One possibility is that young volcanic centers are pres- ent, but have not been identified in the relatively unexplored regions of Chechnya and Dagestan (as perhaps indicated by the 2013 report of a previously unknown Miocene volcanic center in Georgia by [69]. Another possibility is that there may not yet have been enough subduction to generate an ...
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... the slab is clearly imaged by our data in a relatively narrow zone between 45 E and 47 E, understanding the geometry beyond this region and the relative continuity of the structure is essential for understanding the potential seismic hazard. It is unclear if the absence of a coherent zone of sub-crustal seismicity east of 47 E reflects a true lack of a slab or stems from lower- resolution coverage of areas outside of Georgia, particularly in The vertical scale is the same for these four profiles, but the maximum depth displayed differs. Profile X-X is oriented N65 W and is at a different scale than the four NE-SW profiles. Circles indicate earthquake hypocenters and are scaled by magnitude (the same across all five profiles). Earthquakes in white within the NE-SW profiles fall outside the bounds of profile X-X 0 . The colors indicate the distance in the NE-SW direction within profile X-X 0 , with blue near the southern boundary of X-X 0 and dark red at the northern boundary. This color scheme is employed to aid visualization of the NE-SW position of earthquakes in profile X-X 0 . The earthquake swaths in the NE- SW profiles are 30 km wide and the corresponding topographic swaths are 10 km wide. Topography is virtually exaggerated 5Â with the thick black line being the mean topography and the gray bounds corresponding to the minimum and maximum elevations. For profile X-X 0 , the locations of the Greater Caucasus Cenozoic volcanic centers are illustrated above the topography using the same symbols as in Figs. 3 and 4. The calculated convergence above X-X 0 is calculated by subtracting a linear interpolation of the N25 E components of the Lesser Caucasus GPS station velocities from the Greater Caucasus stations, see Forte [35] or Forte et al. [38] for discussion of this calculation. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) the politically volatile areas of Chechnya and Dagestan. Thus, it is also unclear if the slab within the central and eastern Greater Caucasus is continuous with the one beneath the Apsheron Sill identified in previous studies (e.g., [93,53,5]) and imaged by our data ( Fig. S5 and Movie S1). Although we suspect that the slab con- tinues eastward and links with the one beneath the Apsheron Sill, more records of local seismicity are needed to determine if the slabs are continuous or if they are separated by the West Caspian Fault (e.g., [53,6,56]). Southeast of the Greater Caucasus, the West Caspian fault separates the Talysh-Vandam zone to the west from the South Caspian Basin to the east [112]. This transition is marked by both a significant increase in sedimentary thickness from west to east across the fault, and the juxtaposition of continental crust of the Talysh-Vandam zone on the west against oceanic-affinity crust to the east [112,13]. The West Caspian Fault has been interpreted as behaving as a transform fault [64], and thus may represent a potential loci of slab segmentation. Unfortunately, addressing such questions is hampered because access to seismic data in the north- ern Caucasus is difficult, and, due to the location of the Caspian Sea, seismometer locations are not optimal for determining how subduction under the Greater Caucasus relates to that under the Apsheron Sill, nor for providing a strong constraint on the depth and extent of the slab. Fully understanding the nature of this sys- tem will depend on the integration of as many datasets as we can assemble, as there is no near future likelihood of improving seismic coverage in these ...
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... new compilation of local earthquake hypocenters yields evidence of a north-dipping subducted slab beneath the eastern Eurasia [94], divided into stations within the Greater Caucasus (black) and Lesser Caucasus and Rioni/Kura Basins (white) similar to Avdeev and Niemi [8]. Colored symbols are locations of Cenozoic volcanic or intrusive centers within the Greater Caucasus, as discussed in the text (not including volcanic centers that are prevalent in the Lesser Caucasus). Symbols are the same as in Fig. 3. Location of Shatsky Ridge from Nikishin et al. [87] and Dzirula Massif (DM) from Banks et al. [10]. Location of Borjomi-Kazbegi Fault (BKF) from [60]. Borjomi-Kazbegi fault dashed where location is approximate within the Lesser Caucasus and dotted where it is shown in the lower plate, beneath the Greater Caucasus. (b) Perspective view, looking southwest, of a simple block model of the Greater Caucasus system. The surface image is taken from the program Crusta, see text for discussion, and is a visualization of SRTM 90 meter digital elevation data over which a shaded relief map, colored by elevation, is draped. Location of cities, physiographic features, and volcanic provinces shown in Fig. 4a and Movie S1 are displayed. Dark brown colors in cross section and the subsurface indicate continental crust and basement, tan colors indicate sedimentary basins, and gray indicates oceanic crust. Along the eastern edge of the block, we illustrate a cartoon version of the structural geometry within the eastern Greater Caucasus with a prominent fold-thrust belt in the Kura foreland basin [36,37] and a south-dipping thrust system on the northern margin of the range [104]. The northern half of the block is semi- transparent to reveal the inferred slab tear and edge of the eastern slab beneath the central Greater Caucasus, roughly below Grozny. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Greater Caucasus Mountains extending to 100-160 km depth. The western Greater Caucasus (west of 45 E) lack sub-crustal earth- quakes, but contain volcanic centers consistent with formation in a subduction-related volcanic arc, suggesting that subduction may have occurred along the western Greater Caucasus, but that this slab is now detached. The composite catalog clearly demonstrates the presence of a slab beneath the eastern Greater Caucasus, previously a point of debate for several decades. We attribute the lack of traditional geologic evidence of this subduc- tion event within the Greater Caucasus to the relatively modest amount of subduction. The presence of this subduction zone in the eastern and central Greater Caucasus dramatically affects estimates of seismic hazard in this region, as it presents a mecha- nism for generating great (M w P8) earthquakes, consistent with events described in the historical record of seismicity (e.g., [88]). Constraint of the seismic hazard in this region will require a more thorough understanding of the structural geometries beneath the southern margin of the Greater Caucasus and the nature of the linkages between the shallow foreland thrusts and deeper ...
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... absence of an obvious Cenozoic volcanic arc has been used to argue against active subduction beneath the Greater Caucasus (e.g., [98,83]), but this may simply reflect the magnitude, angle, or rate of subduction, or the recency of its initiation. At least five Neogene-Quaternary aged volcanic centers and associated intru- sive centers have been identified in the western Greater Caucasus (Figs. 3 and 4), the structure, deposits, and geochemistry of which are all consistent with genesis in an arc setting (Fig. 3 and Supplemental Text; e.g., [74,66,70,69]). These range in age from late Miocene to Quaternary and include active stratovolcanoes (e.g., Elbrus and Kazbek, [66,65]), a caldera (e.g., Chegem, [74,42]), and granitic to dacitic intrusions (e.g., Elbrus, Kazbek, Lelaashka and Pyatigorsk; ...
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... absence of an obvious Cenozoic volcanic arc has been used to argue against active subduction beneath the Greater Caucasus (e.g., [98,83]), but this may simply reflect the magnitude, angle, or rate of subduction, or the recency of its initiation. At least five Neogene-Quaternary aged volcanic centers and associated intru- sive centers have been identified in the western Greater Caucasus (Figs. 3 and 4), the structure, deposits, and geochemistry of which are all consistent with genesis in an arc setting (Fig. 3 and Supplemental Text; e.g., [74,66,70,69]). These range in age from late Miocene to Quaternary and include active stratovolcanoes (e.g., Elbrus and Kazbek, [66,65]), a caldera (e.g., Chegem, [74,42]), and granitic to dacitic intrusions (e.g., Elbrus, Kazbek, Lelaashka and Pyatigorsk; ...
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... However, not all subduction zones result in ophiolite obduction, and ophiolites in young orogens such as the Greater Caucasus may not yet be exhumed (e.g., Shervais, 2001). As a result, others consider a phase of seafloor spreading an essential component of Caucasus Basin development, given evidence from seismic (e.g., Gunnels et al., 2021;Mumladze et al., 2015;van der Meer et al., 2018), geochemical (Bindeman et al., 2021;Mumladze et al., 2015;Vasey et al., 2021), provenance (Cowgill et al., 2016;Trexler et al., 2022;Vasey, Garcia, et al., 2024), paleomagnetic (van der Boon et al., 2018, and structural (Trexler et al., 2022(Trexler et al., , 2023Tye et al., 2022) data that supports Cenozoic closure of the basin by subduction. ...
... However, not all subduction zones result in ophiolite obduction, and ophiolites in young orogens such as the Greater Caucasus may not yet be exhumed (e.g., Shervais, 2001). As a result, others consider a phase of seafloor spreading an essential component of Caucasus Basin development, given evidence from seismic (e.g., Gunnels et al., 2021;Mumladze et al., 2015;van der Meer et al., 2018), geochemical (Bindeman et al., 2021;Mumladze et al., 2015;Vasey et al., 2021), provenance (Cowgill et al., 2016;Trexler et al., 2022;Vasey, Garcia, et al., 2024), paleomagnetic (van der Boon et al., 2018, and structural (Trexler et al., 2022(Trexler et al., , 2023Tye et al., 2022) data that supports Cenozoic closure of the basin by subduction. ...
... Closure of the Caucasus Basin in response to Arabia-Eurasia began at least by the Eocene to Oligocene (∼35 Ma), given the sedimentary record of a transition from carbonate deposition to siliciclastic deposition dominated by subaerial sediment sources (Vincent et al., 2007, indications of high topography from pollen data , and increased rates of exhumation from thermochronometric data (Avdeev & Niemi, 2011;Forte et al., 2022;Vasey et al., 2020;Vincent et al., 2011Vincent et al., , 2020 at this time. Final closure of the basin likely occurred in the Miocene to Pliocene (∼10-5 Ma) when exhumation rates increased substantially (e.g., Avdeev & Niemi, 2011;Forte et al., 2022;Vasey et al., 2020;Vincent et al., 2011Vincent et al., , 2020 and collisional volcanism began (e.g., Bewick et al., 2022;Bindeman et al., 2021;Lebedev & Vashakidze, 2014;Mitchell & Westaway, 1999;Mumladze et al., 2015). ...
Back‐arc basins frequently form within subduction zones, creating sources of lithospheric weakness that can accommodate subsequent compressional deformation. The crustal structure of these basins, including whether they contain extended preexisting crust and/or new crust formed by seafloor spreading, can thus exert a major influence on strain partitioning in orogenic belts. Here, we present field observations, petrographic analyses, and major/trace element geochemical data from the Caucasus Basin, a back‐arc basin that initiated in continental lithosphere in the Jurassic and subsequently localized deformation in the present‐day Greater Caucasus during the latter stages of Cenozoic Arabia‐Eurasia continent‐continent collision. Our results reveal distinct lithologic and geochemical domains separated by south‐vergent thrust faults within the North Georgia fault system (NGFS) in the Republic of Georgia. Along the Enguri River, shallow intrusive and volcanic rocks are thrust over dominantly volcaniclastic cover, whereas along the Tskhenistskali River, intrusions into metasedimentary rocks are juxtaposed against volcanic flows. The presence of a minor depleted mantle geochemical signature in intrusive rocks from the Tskhenistskali traverse supports an episode of Jurassic seafloor spreading in the Caucasus Basin, with the resulting lithosphere facilitating Cenozoic basin closure by north‐dipping subduction during Arabia‐Eurasia collision. The Khaishi fault along the Enguri River and the Lentekhi fault along the Tskhenistskali river mark major juxtapositions in back‐arc crustal structure and may be components of the terminal suture indicating Caucasus Basin closure. Our results highlight how magmatic rocks in relict basin rocks can yield key insights into basin structure and orogenesis, even when no ophiolite is present.
... Significant debate has centered on the early Cenozoic geometry and dimensions of the GC back-arc basin north of the LC (Cowgill et al., 2016(Cowgill et al., , 2018Vincent et al., , 2018, but paleogeographic reconstructions constrain the NE-SW width to being between 200 and 400 km (van der Boon et al., 2018;van Hinsbergen et al., 2019;Darin and Umhoefer, 2022), similar to the dimensions of the Black Sea and South Caspian Basins, which are likely remnants of the same back-arc basin system (Zonenshain and Le Pichon, 1986). Timing of initiation of closure and shortening of the GC back-arc basin is unclear but had likely begun by the Eocene-Oligocene (e.g., Vincent et al., 2007) and was accommodated in part by northward subduction of oceanic or transitional lithosphere, based on seismic evidence of a subducted slab in the eastern GC (Skobeltsyn et al., 2014;Mumladze et al., 2015;Gunnels et al., 2020). The timing of the transition from subduction to collision and beginning of significant upper-plate shortening and exhumation has also proven controversial, but recent new results from, and syntheses of, low-temperature thermochronology data have largely confirmed the original suggestion by Avdeev and Niemi (2011) of initiation of rapid exhumation between 10 and 5 Ma throughout much of the range (e.g., Vincent et al., 2020;Forte et al., 2022;Tye et al., 2022;Cavazza et al., 2023). ...
The Greater Caucasus (GC) mountains are the locus of post-Pliocene shortening within the northcentral Arabia-Eurasia collision. Although recent low-temperature thermochronology constrains the timing of orogen formation, the evolution of major structures remains enigmatic—particularly regarding the internal kinematics within this young orogen and the associated Kura Fold-Thrust Belt (KFTB), which flanks its southeastern margin. Here we use a multiproxy provenance analysis to investigate the tectonic history of both the southeastern GC and KFTB by presenting new data from a suite of sandstone samples from the KFTB, including sandstone petrography, whole-rock geochemistry, and detrital zircon (DZ) U-Pb geochronology. To define source terranes for these sediments, we integrate additional new whole-rock geochemical analyses with published DZ results and geological mapping. Our analysis reveals an apparent discrepancy in up-section changes in provenance from the different methods. Sandstone petrography and geochemistry both indicate a systematic up-section evolution from a volcanic and/or volcaniclastic source, presently exposed as a thin strip along the southeastern GC, to what appears similar to an interior GC source. Contrastingly, DZ geochronology suggests less up-section change. We interpret this apparent discrepancy to reflect the onset of sediment recycling within the KFTB, with the exhumation, weathering, and erosion of early thrust sheets in the KFTB resulting in the selective weathering of unstable mineral species that define the volcaniclastic source but left DZ signatures unmodified. Using the timing of sediment recycling and changes in grain size together as proxies for structural initiation of the central KFTB implies that the thrust belt initiated nearly synchronously along strike at ~2.0–2.2 Ma.
... The Greater Caucasus Mountains extend for 900 km between the Black and Caspian Seas ( Figure 1) and were uplifted since ∼5 Ma due to the northeast-directed subduction of the Arabian plate beneath the Eurasian plate (Avdeev & Niemi, 2011;Cowgill et al., 2016;Forte et al., 2015;Gunnels et al., 2021;Jackson et al., 2002;Kangarli et al., 2018;McKenzie, 1972;Mumladze et al., 2015;Philip et al., 1989). High resolution 3-D tomogographic models and relocated earthquake hypocenters suggest that this subduction is active and ongoing beneath the eastern part of the Greater Caucasus in Azerbaijan (Gunnels et al., 2021). ...
Here we present the results of the first paleoseismic study of the Kura fold‐thrust belt in Azerbaijan based on field mapping, fault trenching, and Quaternary dating. Convergence at rates of ∼10 mm/yr between the Arabian and Eurasian Plates is largely accommodated by the Kura fold‐thrust belt which stretches between central Azerbaijan and Georgia along the southern front of the Greater Caucasus (45–48°E). Although destructive historic earthquakes are known here, little is known about the active faults responsible for these earthquakes. A paleoseismic trench was excavated across a 2‐m‐high fault scarp near Agsu revealing evidence of two surface rupturing earthquakes. Radiocarbon dating of the faulted sediments limits the earthquake timing to AD 1713–1895 and AD 1872–2003. Allowing for uncertainties in dating, the two events likely correspond to historical destructive M ∼ 7 earthquakes near Shamakhi, Azerbaijan in AD 1668 and 1902. A second trench 60 km west of Agsu was excavated near Goychay also revealing evidence of at least one event that occurred 334–118 BC. Holocene shortening and dip‐slip rates for the Kura fold‐thrust belt are ∼8.0 and 8.5 mm/yr, respectively, based on an uplifted strath terrace west of Agsu. The only known historical devastating (M > ∼7) earthquakes in the Kura region, west of Shamakhi, occurred in 1139 and possibly 1668. The lack of reported historical ruptures from the past 4–8 centuries in the Kura, in contrast with the numerous recorded destructive earthquakes in Shamakhi, suggests that the Kura fold‐thrust belt may have accumulated sufficient strain to produce a M > 7.7 earthquake.
... If we consider the Greater Caucasus Range, earthquakes are distributed along its margins, while the axial zone is aseismic except for the eastern part, where the presence of a subduction tectonic mechanism is assumed [10]. The presence of a seismic gap along the axial line of the Greater Caucasus Range is also discussed in [27]. ...
This paper analyzes and reviews the rapid uplifts of the Earth’s crust in the Caucasus that occurred over the last century. The uplifts were registered by precise repeated state leveling and reflected on officially published maps of vertical movements of the Earth’s crust. This study summarizes information on the region’s vertical movements over more than a century. The present study describes the technology for creating maps of recent vertical movements of the Earth’s crust using precision leveling data. This paper summarizes cases of recording uplifts of the Earth’s surface in other regions of the world in connection with seismic activity. The authors carried out intercomparison of vertical movements with tectonics, seismicity, and geophysical fields, which discovered their apparent mutual correspondence. This indicates the deep tectonic nature of the observed uplifts of the Earth’s crust. Spatial and temporal agreement with the distribution of strong earthquakes showed a natural relationship. It has been shown that strong earthquakes are confined to the boundaries of zones of rapid uplift. They occur predominantly in areas of transition between uplifts and subsidence. The results obtained demonstrate the role of the study and observations of vertical movements of the Caucasus in assessing periods and areas of increased seismic hazard.
... Compressional buckling may have caused uplift of the Greater Caucasus and subsidence around them to create the deep basins, including the Rioni-Kura Basin. The only block with deep and localized, present day seismicity in the area indicates that any subduction structure must be located to the north of the greater Caucasus at a very steep angle (Mumladze et al., 2015). ...
The Central Tethys realm including Anatolia, Caucuses and Iranian plateau is one of the most complex geodynamic settings within the Alpine-Himalayan belt. To investigate the tectonics of this region, we estimated the depth to magnetic basement (DMB), as a proxy for the shape of sedimentary basins, and average crustal magnetic susceptibility (ACMS) by applying the fractal spectral method to the aeromagnetic data. Magnetic data is sensitive to the presence of iron-rich minerals in oceanic fragments and mafic intrusions, hidden beneath sedimentary sequences or overprinted by younger tectono-magmatic events. Furthermore, a seismically constrained 2D density-susceptibility model along Zagros is developed to study depth extension of structures.
By comparing the DMB with ACMS, we conclude:
High ACMS indicates steep and gentle lineaments that correlate with known occurrences of Magmatic-Ophiolite Arcs (MOA) and low ACMS coincides with known sedimentary basins in the study region such as Zagros. We identify hitherto unknown parallel MOAs below the sedimentary cover in eastern Iran and the SE part of Urima-Dokhtar Magmatic Arc (UDMA). The result allows for estimation of the dip of paleo-subduction zones.
Known magmatic arcs (Pontides and Urima-Dokhtar) have high-intensity heterogeneous ACMS. We identify a 450 km-long buried (DMB >6 km) magmatic arc or trapped oceanic crust along the western margin of the Kirşehır massif from a strong ACMS anomaly. Large, partially buried magmatic bodies form the Caucasus LIP at the Transcaucasus and Lesser Caucasus and in NW Iran. ACMS anomalies are weak at tectonic boundaries and faults. However, the Cyprus subduction zone has a strong magnetic signature which extends ca. 500 km into the Arabian plate.
We derive a 2D crustal-scale density-susceptibility model of the NW Iranian plateau along a 500 km long seismic profile across major tectonic provinces of Iran from the Arabian plate to the South Caspian Basin (SCB). The seismic P-wave receiver function section is used to constrain major crustal boundaries in the density model.
We demonstrate that the Main Zagros Reverse Fault (MZRF), between the Arabian and the overriding Central Iran crust, dips at ~13° angle towards NE and extends to a depth of ~40 km. The trace of MZRF suggests ~150 km underthrusting of the Arabian plate beneath Central Iran. We identify a new crustal-scale suture beneath the Tarom valley separating the South Caspian Basin curst from the Central Iran. The high density lower crust beneath Alborz and Zagros might possibly be related to partial eclogitization of the crustal root at depths deeper than ~40 km.
... However, recent work challenges this model. Seismicity datasets reveal subduction of possible oceanic lithosphere beneath the eastern GC (e.g., Mumladze et al., 2015;Gunnels et al., 2021), which suggests the basin was at least wide enough for subduction to initiate. In addition, contrasts in sedimentary provenance indicate the inverted basin was too wide for there to be sedimentary exchange between its northern and southern margins, suggesting that it was potentially hundreds of km wide (Figure 1b Cowgill et al., 2016;Tye et al., 2021). ...
... Crustal thickness in the GC ranges from 36 km in the western part of the orogen to nearly 50 km in the east, as constrained by regional tomographic studies (Zor, 2008). Deep (>150 km) seismicity beneath the eastern part of the range has been interpreted as evidence of subduction during basin closure, with the notable absence of deep earthquakes beneath the western half of the range inferred to be the result of recent slab detachment (Mumladze et al., 2015). This model has since been reinforced by documentation of oceanic lithosphere beneath the Kura foreland basin in the eastern GC (Gunnels et al., 2021), and has been suggested to explain geochemical signatures of arc magmatism found in the GC (Vasey et al., 2021) and significant plate convergence between the Greater and Lesser Caucasus inferred by paleomagnetism datasets (van der Boon et al., 2018) and plate boundary reconstruction studies (Darin and Umhoefer, 2022). ...
... Importantly, our cross sections allow for additional shortening via underthrusting or subduction along one or several of the faults within the NGFS, providing a mechanism wherein these models could easily accommodate several hundred km or more of additional shortening, consistent with prior work that has suggested 350 km of total shortening across the GC (Cowgill et al., 2016;van der Boon et al., 2018;Darin and Umhoefer, 2022). A significant magnitude of shortening via underthrusting or subduction may even be expected, particularly along the central GC transect, where a north-dipping zone of seismicity in the mantle delineates a subducting plate (e.g., Mumladze et al., 2015). ...
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.
... For these deep areas lithospheric interactions is a mechanism of feeding the volcanoes due to the delaminated (missing) lithosphere detached due to collisional processes and overheated asthenosphere appears to be very close to the bottom of the crust and heats the crustal rocks, leads to active melting and forming magma reservoirs. Also, we infer that the occurrence of deep earthquakes (for example 2015-09-12 02:08:49, Latitude 43.67 • N, Longitude 45.74 • E, depth 121.66 m, M4, NEIC, eastern Caucasus in our study) could be a reason of thermal interactions beneath the Caucasus (east to west) due to active subduction (subducted, detached, and torn slabs) which presents a potentially larger seismic hazard than previously recognized and may explain historical records of large magnitude (∼8) seismicity in this region [e.g., Mumladze et al., 2015]. These commentaries are in good agreement with observed low-velocity anomalies at long-periods in Caucasus [e.g., Koulakov et al., 2012]. ...
In order to better understand the regional tectonic activities of the continent-continent ongoing collision-compressed edge zone of the Eurasian-Arabic plates, 2D tomography maps of the Caucasus territory using the Rayleigh waves were generated. The 2D tomography images of this study, illustrate the large variety in surface wave propagation velocity in different complex geologic units of the Caucasus. To draw the 2D tomography maps, we accomplished a 2D-linear inversion procedure on the Rayleigh wave dispersion curves for the periods of 5 to 70 s (depth= ~180 km). To conduct this, local-regional data from ~1300 earthquakes (M≥3.9) recorded by the 49 broadband stations from 1999 to 2018 in a wide area with complicated tectonic units were used. In comparison with results of previous studies in Caucasus, the tomography maps for the long-periods (T= 50-70 s; depth ~180 km) are more influenced by the velocity structure of the uppermost mantle which demonstrate the ultralow and ultrahigh-velocity anomalies. The results for the medium-periods (30≤T≤45 s), the low-velocity zones coincide with areas thought to be correlated with underplating of the lower crust (e.g. shallow LAB), while, the high-velocity zones are usually demonstrating the presence of a normal continental crust over a stable and thick or oceanic-like lid. Short-periods (5≤T≤25 s) are more influenced by the ever-evolving deformations of the geological units, sedimentary basins, volcanic complexes, uplifts, and reveals a low-velocity small zone, on the NW slope of the Aragats volcano (depth= ~7 km), which is different from the results of other studies.
... We do not observe magnetic pattern typical of magmatic arcs along the strike of the Greater Caucasus and emphasize that neither gravity modeling (Kaban et al., 2018), nor the seismicity pattern support geodynamic models for subduction beneath the Greater Caucasus region. The only block with deep, localized, present-day seismicity in the area indicates that any subduction relic must be local and to the north of the Greater Caucasus at a very steep angle (Mumladze et al., 2015). We are also unaware of regional processes which may have caused demagnetization of the entire Greater Caucasus magmatic arc, if it existed. ...
We calculate the depth to magnetic basement and the average crustal magnetic susceptibility, which is sensitive to the presence of iron‐rich minerals, to interpret the present structure and the tecto‐magmatic evolution in the Central Tethyan belt. Our results demonstrate exceptional variability of crustal magnetization with smooth, small‐amplitude anomalies in the Gondwana realm and short‐wavelength high‐amplitude variations in the Laurentia realm. Poor correlation between known ophiolites and magnetization anomalies indicates that Tethyan ophiolites are relatively poorly magnetized, which we explain by demagnetization during recent magmatism. We analyze regional magnetic characteristics for mapping previously unknown oceanic fragments and mafic intrusions, hidden beneath sedimentary sequences or overprinted by tectono‐magmatic events. By the style of crustal magnetization, we distinguish three types of basins and demonstrate that many small‐size basins host large volumes of magmatic rocks within or below the sedimentary cover. We map the width of magmatic arcs to estimate paleo‐subduction dip angle and find no systematic variation between the Neo‐Tethys and Paleo‐Tethys subduction systems, while the Pontides magmatic arc has shallow (∼15°) dip in the east and steep (∼50°–55°) dip in the west. We recognize an unknown, buried 450 km‐long magmatic arc along the western margin of the Kırşehir massif formed above steep (55°) subduction. We propose that lithosphere fragmentation associated with Neo‐Tethys subduction systems may explain high‐amplitude, high‐gradient crustal magnetization in the Caucasus Large Igneous Province. Our results challenge conventional regional geological models, such as Neo‐Tethyan subduction below the Greater Caucasus, and call for reevaluation of the regional paleotectonics.
... The tectonic setting of the Greater Caucasus varies along strike (Figure 2a; Forte et al., 2014). The western Greater Caucasus accommodates 4 mm/yr convergence (Reilinger et al., 2006;Sokhadze et al., 2018), is characterized structurally by coherent macro-scale thrust sheets of 2-10 km thickness (Trexler et al., 2022), and has earthquake depths of <20 km (Mumladze et al., 2015). In contrast, the eastern Greater Caucasus is accommodating convergence rates of 10-12 mm/yr (Figure 2a; Kadirov et al., 2012Kadirov et al., , 2015Reilinger et al., 2006) and earthquake depths of up to >100 km have been recorded north of the range (Burmin et al., 2019;Gunnels et al., 2021;Mellors et al., 2012;Mumladze et al., 2015). ...
... The western Greater Caucasus accommodates 4 mm/yr convergence (Reilinger et al., 2006;Sokhadze et al., 2018), is characterized structurally by coherent macro-scale thrust sheets of 2-10 km thickness (Trexler et al., 2022), and has earthquake depths of <20 km (Mumladze et al., 2015). In contrast, the eastern Greater Caucasus is accommodating convergence rates of 10-12 mm/yr (Figure 2a; Kadirov et al., 2012Kadirov et al., , 2015Reilinger et al., 2006) and earthquake depths of up to >100 km have been recorded north of the range (Burmin et al., 2019;Gunnels et al., 2021;Mellors et al., 2012;Mumladze et al., 2015). Recent tomographic results indicate that the Kura foreland basin, which is being underthrust beneath the eastern Greater Caucasus, is floored by thin (<20 km thick), mafic crust ( Figure 2b; Gunnels et al., 2021). ...
... Schematic geology is shown following the key in (b), based on previous regional mapping (Nalivkin, 1976). White annotation shows geodetic convergence rates (Reilinger et al., 2006), location of a high crustal seismic velocity zone beneath the Kura and South Caspian basins inferred to reflect mafic (possibly oceanic) composition (Gunnels et al., 2021), and the along-strike extent of a subducting slab inferred beneath the range from deep earthquakes (Mumladze et al., 2015). (b) Map showing schematic geology of the eastern Greater Caucasus study area, modified after Bairamov et al. (2008) and Nalivkin (1976), using the same symbology as in (a). ...
Orogenic wedges are common at convergent plate margins and deform internally to maintain a self‐similar geometry during growth. New structural mapping and thermochronometry data illustrate that the eastern Greater Caucasus mountain range of western Asia undergoes deformation via distinct mechanisms that correspond with contrasting lithologies of two sedimentary rock packages within the orogen. The orogen interior comprises a package of Mesozoic thin‐bedded (<10 cm) sandstones and shales. These strata are deformed throughout by short‐wavelength (<1 km) folds that are not fault‐bend or fault‐propagation folds. In contrast, a coeval package of thick‐bedded (up to 5 m) volcaniclastic sandstone and carbonate, known as the Vandam Zone, has been accreted and is deformed via imbrication of coherent thrust sheets forming fault‐related folds of 5–10 km wavelength. Structural reconstructions and thermochronometric data indicate that the Vandam Zone package was accreted between ca. 13 and 3 Ma. Following Vandam Zone accretion, thermal modeling of thermochronometric data indicates rapid exhumation (∼0.3–1 mm/yr) in the wedge interior beginning between ca. 6 and 3 Ma, and a novel thermochronometric paleo‐rotation analysis suggests out‐of‐sequence folding of wedge‐interior strata after ca. 3 Ma. Field relationships suggest that the Vandam Zone underwent syn‐convergent extension following accretion. Together, the data record spatially and temporally variable deformation, dependent on both the mechanical properties of deforming lithologies and perturbations such as accretion of material from the down‐going to the overriding plate. The diverse modes of deformation are consistent with the maintenance of critical taper.
... Recently, most of the research efforts of the Caucasian countries have been focused on the recalculation of earthquake hypocenters to decrease the current uncertainties (e.g. Tsereteli et al. 2012Tsereteli et al. , 2016Mumladze et al., 2015;Adamia et al., 2017;Kazimova et al., 2017). ...
... In more detail, most of the events are located along the southern and northern foothill regions, whereas a smaller subset of events is located along the GC axis. Moreover, we confirm the general decrease of seismicity in the western regions, as already put forward by other authors (Mumladze et al., 2015, and references therein). In Fig. 5, we observe a correlation between the main active faults of the GC and the earthquakes epicentres. ...
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 northeastern 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 overall occurrence of earthquakes of minor and major magnitude. Main earthquakes are characterized by a vertical least principal stress (σ 3), corresponding to reverse kinematics. Reverse slip is more common along the southwestern and northeastern 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.
