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![(a) Location of Arabia-Eurasia collision zone within the Alpine-Himalayan belt. GC = Greater Caucasus. Box outlines bounds of Fig. 1b. (b) First-order structures within the Arabia-Eurasia collision zone. Dark gray zones in Black and Caspian seas indicate location of oceanic crust beneath the South Caspian Basin (SCB, [102]) and Eastern and Western Black Sea Basins (EBB and WBB, [87]). The red zone in the Black Sea is Shatsky Ridge (SR, [87]). Arrows indicate motion of Arabia relative to stable Eurasia from the REVEL 2000 velocity model [99]. Smaller black box outlines bounds of Fig. 1c. and larger box outlines Fig. 4b. Abbreviations are as follows: NAF = North Anatolian Fault, EAF = East Anatolian Fault, DSF = Dead Sea Fault, AS = Apsheron Sill. (c) Greater and Lesser Caucasus region with main physiographic features labeled, along with major population centers and infrastructure. Circles with black outlines are earthquakes discussed in this work with depths greater than 50 km with their size scaled by magnitude and colored by depth. Locations and sizes of isoseismals for events with magnitudes greater than 9 in the Caucasus regions [88,14]. The black brackets indicate the positions of the profiles shown in Fig. 2. Note that the wide part of the brackets indicate the width of the earthquake swath and the thinner, inset bracket indicates the width of the associated topographic swath. Base maps for all figures are shaded relief maps derived from SRTM 90 meter resolution data. (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/fig1/AS:613971778342922@1523393687684/a-Location-of-Arabia-Eurasia-collision-zone-within-the-Alpine-Himalayan-belt-GC.png)
(a) Location of Arabia-Eurasia collision zone within the Alpine-Himalayan belt. GC = Greater Caucasus. Box outlines bounds of Fig. 1b. (b) First-order structures within the Arabia-Eurasia collision zone. Dark gray zones in Black and Caspian seas indicate location of oceanic crust beneath the South Caspian Basin (SCB, [102]) and Eastern and Western Black Sea Basins (EBB and WBB, [87]). The red zone in the Black Sea is Shatsky Ridge (SR, [87]). Arrows indicate motion of Arabia relative to stable Eurasia from the REVEL 2000 velocity model [99]. Smaller black box outlines bounds of Fig. 1c. and larger box outlines Fig. 4b. Abbreviations are as follows: NAF = North Anatolian Fault, EAF = East Anatolian Fault, DSF = Dead Sea Fault, AS = Apsheron Sill. (c) Greater and Lesser Caucasus region with main physiographic features labeled, along with major population centers and infrastructure. Circles with black outlines are earthquakes discussed in this work with depths greater than 50 km with their size scaled by magnitude and colored by depth. Locations and sizes of isoseismals for events with magnitudes greater than 9 in the Caucasus regions [88,14]. The black brackets indicate the positions of the profiles shown in Fig. 2. Note that the wide part of the brackets indicate the width of the earthquake swath and the thinner, inset bracket indicates the width of the associated topographic swath. Base maps for all figures are shaded relief maps derived from SRTM 90 meter resolution data. (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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... to previous work (e.g., [80]), we consider any earth- quake deeper than 50 km to be sub-crustal. This cut-off comes from estimates of average crustal thickness of 45-50 km in the Greater Caucasus region derived from results of deep seismic soundings [62], receiver functions and surface wave studies [46], and upper mantle P-wave tomography [121]. Although most earth- quakes within the Greater Caucasus are restricted to the crust (depths <50 km), east of 45 E there are numerous events deeper than 50 km, with some >150 km (Figs. 1, 2, S3, S4, S5 and Movie S1; e.g., [80]. Between 45 E and 47 E, these deep earthquakes define a northeast dipping plane of seismicity that is located along the northern boundary of the Greater Caucasus (Figs. 2, S5 and Movie S1). The western boundary of this zone of deep earthquakes is nearly coincident with the location of the proposed Borjomi- Kazbegi fault ( Fig. 4; e.g., [58,92,60]). West of the proposed Borjomi-Kazbegi fault and 45 E there is a marked absence of earth- quakes deeper than 50 km, which we attribute to a true lack of deep events because the densest coverage of seismic stations is within this portion of the range in ...
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... in event locations are generally unavailable in the original sources from which the composite catalog was compiled. To assess such uncertainties, we conducted three analyses. First, we evaluated uncertainties determined using HYPO71 and reported in an unpublished (and not yet publicly available) database of events maintained by the SMC. The distribution of hor- izontal and vertical uncertainties is shown in Figure S1 for the 505 events within Catalog #1 for which we have uncertainty informa- tion. The uncertainty values themselves are part of the as yet unpublished, full catalog from which Catalog #1 is derived. Aver- age horizontal and vertical uncertainties are 2:00 AE 1:47 km and 2:21 AE 1:42 km (AE1r), respectively. Second, Table S3 compares locations for 23 events reported by all four recent catalogs (#0- 3). The standard errors for each set of 4 independent depth deter- minations range from a minimum of 0.3 km to a maximum of 17.1 km. Third, to check locations of older events in Catalog #5, we searched for arrival time information in Georgian records of the 27 events in our catalog, which yielded information for 9 events, 3 of which had sufficient information to recalculate hypo- centers. All 3 events remain at subcrustal depths, with differences in depth of 13.6 to 18.4 km between the original (Catalog #5) and recalculated locations (Tables S2 and ...
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... analyze the database, we examined hypocenter locations using standard 2-D profiles (Figs. 1, 2, S3 and S4) and free, open- source software developed by the W.M. Keck Center for Active Visualization in the Earth Sciences (KeckCAVES, http:// www.keckcaves.org) running on both a desktop computer and in a CAVE immersive visualization environment ( Fig. S5 and Movie S1). As explained elsewhere [23], use of this software in a CAVE generates the experience of spatial presence, where users believe they are physically located within a virtual environment (e.g., within the earth) rather than in their true physical location (e.g., in a laboratory; ...
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... speculate that the western slab (i.e., portion of former slab west of 45 E) detached in response to attempted subduction of the continental Shatsky Ridge and Dzirula Massif, which may have stalled subduction and led to detachment (Figs. 1 and 4). Attempted subduction of continental lithosphere is commonly cited as driving initiation of slab detachment (e.g., [24,20]). The Shatsky Ridge, which lies mostly offshore along the northeastern boundary of the Black Sea, and the Dzirula Massif, which is inter- preted as the onshore continuation of the Shatsky Ridge, are thought to be cored by continental basement and to have formed a single paleo-high that originally divided rift sub-basins within the Black Sea [10], and in particular separated the Eastern Black Sea Basin to the southwest from the former Greater Caucasus Basin to the northeast [87]. While no longer a bathymetric feature within the Black Sea, the buoyancy of the Shatsky Ridge is suggested by its associated strong negative gravity anomaly (À60 mGal free-air, ...
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... potential slab tear and beginning phases of slab detachment of the eastern Greater Caucasus slab may also be driven by the attempted subduction of more buoyant, continental lithosphere. The location of the tear is largely coincident with an area in which the Greater and Lesser Caucasus appear to be colliding, with a south-verging thrust system from the Greater Caucasus overriding north-verging structures of the Lesser Caucasus ( Fig. 1; e.g., ...
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... on the available data, a true assessment of magnitudes of potential earthquakes is not yet possible. However, such work is critically important because even earthquakes of intermediate magnitude may lead to devastating human impact in this region, as demonstrated by the 1988 M s 6.8 Spitak earthquake in the Lesser Caucasus, which killed over 25,000 people [22]. Importantly, we note that many of the main population centers and areas of critical infrastructure within the southern Greater Caucasus are underlain by the shallow, north-dipping foreland structures and would likely experience significant shaking during a large magni- tude earthquake (Fig. 1). The historical record of seismicity in the southern Greater Caucasus is consistent with this hypothesis, as regions underlain by the eastern Greater Caucasus slab or its up- dip continuation beneath the Kura fold-thrust belt correspond to areas that record large historical earthquakes ( Figs. 1 and 4; ...
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... on the available data, a true assessment of magnitudes of potential earthquakes is not yet possible. However, such work is critically important because even earthquakes of intermediate magnitude may lead to devastating human impact in this region, as demonstrated by the 1988 M s 6.8 Spitak earthquake in the Lesser Caucasus, which killed over 25,000 people [22]. Importantly, we note that many of the main population centers and areas of critical infrastructure within the southern Greater Caucasus are underlain by the shallow, north-dipping foreland structures and would likely experience significant shaking during a large magni- tude earthquake (Fig. 1). The historical record of seismicity in the southern Greater Caucasus is consistent with this hypothesis, as regions underlain by the eastern Greater Caucasus slab or its up- dip continuation beneath the Kura fold-thrust belt correspond to areas that record large historical earthquakes ( Figs. 1 and 4; ...
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... asymmetric distribution of deep earthquakes along strike is particularly striking in the dataset, with a lack of sub-crustal events west of 45 E but clear evidence of earthquakes at mantle depths to the east (Fig. 2). Previous studies have noted both this pattern and similar along-strike variations in other aspects of the crustal structure of the Greater Caucasus (e.g., [80,46,97]). Unlike in the eastern part of the range, data coverage within Georgia is dense, therefore, the lack of deep seismicity west of 45 E most likely indicates a true lack of subcrustal seismicity in this region. We interpret the lack of subcrustal seismicity as evidence of recent slab detachment based on both previous reports of anomalously low subsidence in the northwestern foreland of the Greater Cauca- sus (i.e. subsidence rates in the foreland that are lower than those expected based on simple flexural models and the known volume of the range; e.g., [81,32]) and low upper-mantle seismic velocities west of 47 E in most tomographic models of the range [63,76,103]. These observations led previous workers to hypothesize a compo- nent of dynamically driven uplift of the foreland due to a delami- nation event beneath the western Greater Caucasus [33,121,63]. Here, we suggest that this delamination was the detachment of a subducted slab, as opposed to the removal of a dense crustal root as proposed by Ershov et al. [33] and Koulakov et al. [63]. Numer- ical models indicate slab detachment can cause significant rock uplift (e.g., [19]), consistent to a first order with the observation of uplift of the northwestern Greater Caucasus foreland presented by Ershov et al. [33]. Additionally, a tomographic model of the wes- tern Arabia-Eurasia collision zone imaged a zone of anomalously fast Pn velocity north of the central Greater Caucasus and near the edge of the modeled domain (e.g., [3]), which we suggest could be the detached slab. The concentration of deep earthquakes in the eastern portion of the Greater Caucasus, especially in the vicinity of Grozny (Fig. 1), could be interpreted in terms of crustal delamina- tion or a drip, however, we do not favor this interpretation because of the consistent northward dip of the seismicity, its continuity for >400 km along strike, tomographic results that indicate crustal thicknesses of $50km in the eastern Greater Caucasus [121], and the location of the majority of these deep events along the flanks of the range or in the northern foreland, offset >100 km from the high topography of the range. The high topography of the Greater Caucasus has also been explained in terms of ''dynamic topogra- phy'' generated by small-scale mantle flow without subduction [34]. We do not consider this model a robust explanation for the earthquake distributions presented here or the geology of the Greater Caucasus because the small-scale convection model pre- dicts only uplift and no observable surface shortening, which is demonstrably false given the geology of the fringing fold-thrust belts (e.g., [36,37]). In addition this model predicts mantle flow parallel to the strike of the range, perpendicular to observed convergence directions [94]. It is possible that small-scale mantle convection could contribute to the topography of the Greater Caucasus, but if it is acting in this region, it is occurring in concert with shortening driven by subduction ...
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... Greater Caucasus Mountains are located between the Black and Caspian Seas, $500 km north of the main Arabia-Eurasia plate boundary, and are presently the main locus of active NE-SW directed plate convergence in this central portion of the collision ( Fig. 1; e.g., [52,4,94]). Potential earthquake sources are often obscure in such intracontinental regions, due to their distance from plate boundaries [31]. Instrumentally measured earthquakes in the Greater Caucasus region are generally modest (M w < 6, [93,53,29,107]), with the largest recorded earthquake being the M w 6.9 1991 Racha event along the southwestern flank of the range ( Fig. 1; [108,39,107]). However, historical records in the region extend back to $2000 B.C. (e.g., [61,101]) and suggest numerous larger earthquakes (e.g., [17,88,61,14,25,47,101]). These include an event in 1668 centered near Sheki, Azerbaijan that may have exceeded M 8 and that completely destroyed the city of Shemakha, killing $80,000 people (e.g., ...
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... Greater Caucasus Mountains are located between the Black and Caspian Seas, $500 km north of the main Arabia-Eurasia plate boundary, and are presently the main locus of active NE-SW directed plate convergence in this central portion of the collision ( Fig. 1; e.g., [52,4,94]). Potential earthquake sources are often obscure in such intracontinental regions, due to their distance from plate boundaries [31]. Instrumentally measured earthquakes in the Greater Caucasus region are generally modest (M w < 6, [93,53,29,107]), with the largest recorded earthquake being the M w 6.9 1991 Racha event along the southwestern flank of the range ( Fig. 1; [108,39,107]). However, historical records in the region extend back to $2000 B.C. (e.g., [61,101]) and suggest numerous larger earthquakes (e.g., [17,88,61,14,25,47,101]). These include an event in 1668 centered near Sheki, Azerbaijan that may have exceeded M 8 and that completely destroyed the city of Shemakha, killing $80,000 people (e.g., ...
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... 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.
... Adding to the complication, the gross topography of the GC, which is characterized by relative uniformity, seemed at odds with modern climatic and tectonic forcing . In detail, isostatic response to the detachment of a subducted slab beneath the western GC (Mumladze et al., 2015), may contribute some to nearly all of the observed rapid exhumation within the western GC (Vincent et al., 2020). In contrast, clear evidence of a still extant, attached slab in the eastern GC (e.g., Gunnels et al., 2020;Mellors et al., 2012;Mumladze et al., 2015;Skolbeltsyn et al., 2014) seems compatible with shortening, accretion, and crustal thickening as the primary drivers of exhumation and topographic growth . ...
... In detail, isostatic response to the detachment of a subducted slab beneath the western GC (Mumladze et al., 2015), may contribute some to nearly all of the observed rapid exhumation within the western GC (Vincent et al., 2020). In contrast, clear evidence of a still extant, attached slab in the eastern GC (e.g., Gunnels et al., 2020;Mellors et al., 2012;Mumladze et al., 2015;Skolbeltsyn et al., 2014) seems compatible with shortening, accretion, and crustal thickening as the primary drivers of exhumation and topographic growth . However, the operation of differing dominant exhumation mechanisms along-strike are challenging to test because the vast majority of published low-temperature thermochronology data lie within the region that may have experienced slab detachment (e.g., Král & Gurbanov, 1996;Vasey et al., 2020;Vincent et al., 2011Vincent et al., , 2020. ...
... The closure of the GC back-arc basin represented the last in a series of similar intervening basin closures further south within the central Arabia-Eurasia collision (e.g., Cowgill et al., 2016;Golonka, 2004;van Hinsbergen et al., 2019;Vasey et al., 2020). The closure and shortening of the GC back-arc basin was accommodated at least in part by the northward subduction of oceanic to transitional crust, which originally floored the basin (e.g., Mumladze et al., 2015). A remnant of this subducted slab is preserved in the eastern GC (Mellors et al., 2012;Mumladze et al., 2015;Skolbeltsyn et al., 2014) and appears continuous with active, northward subduction of the South Caspian oceanic lithosphere beneath the middle Caspian Basin (Gunnels et al., 2020). ...
The Greater Caucasus (GC) Mountains within the central Arabia‐Eurasia collision zone are an archetypal example of a young collisional orogen. However, the mechanisms driving rock uplift and forming the topography of the range are controversial, with recent provocative suggestions that uplift of the western GC is strongly influenced by an isostatic response to slab detachment, whereas the eastern half has grown through shortening and crustal thickening. Testing this hypothesis is challenging because records of exhumation rates mostly come from the western GC, where slab detachment may have occurred. To address this data gap, we report 623 new, paired zircon U‐Pb and (U‐Th)/He ages from seven different modern river sediments, spanning a ∼400 km long gap in bedrock thermochronometer data. We synthesize these with prior bedrock thermochronometer data, recent catchment averaged ¹⁰Be cosmogenic exhumation rates, topographic analyses, structural observations, and plate reconstructions to evaluate the mechanisms growing the GC topography. We find no evidence of major differences in rates, timing of onset of cooling, or total amounts of exhumation across the possible slab edge, inconsistent with previous suggestions of heterogeneous drivers for exhumation along‐strike. Comparison of exhumation across timescales highlight a potential acceleration, but one that appears to suggest a consistent northward shift of the locus of more rapid exhumation. Integration of these new datasets with simple models of orogenic growth suggest that the gross topography of the GC is explainable with traditional models of accretion, thickening, and uplift and does not require any additional slab‐related mechanisms.
