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![Swath profiles of earthquake hypocenters and topography; refer to Fig. 1c for profile locations. Profiles A-A 0 , B-B 0 , C-C 0 , and D-D 0 are oriented N25 E and share the same horizontal scale. 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 NESW 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.)](profile/Nathan-Niemi/publication/269391445/figure/fig2/AS:613971778359355@1523393687909/Swath-profiles-of-earthquake-hypocenters-and-topography-refer-to-Fig-1c-for-profile.png)
Swath profiles of earthquake hypocenters and topography; refer to Fig. 1c for profile locations. Profiles A-A 0 , B-B 0 , C-C 0 , and D-D 0 are oriented N25 E and share the same horizontal scale. 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 NESW 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.)
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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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... northeast-dipping plane of seismicity has an apparent dip of $ 40 and a maximum depth that decreases eastwards (Figs. 2, S5 and Movie S1). At the western end of the zone of seismicity, there is a discontinuity in seismicity down dip, with a lack of $50 km deep events (see profiles B-B 0 and X-X 0 in Fig. 2). While there are other partial gaps in seismicity, this is the largest contin- uous aseismic region in the dipping zone of seismicity, continuing for $100 km along strike (X-X 0 in Fig. 2) and up to $50 km down dip (B-B 0 and X-X 0 in Fig. 2). As with the maximum earthquake depths, the width of the discontinuity also decreases eastwards (from position 350 to 450 km on profile X-X 0 in Fig. 2) until the zone of deep earthquakes eventually merges with those in the crust. The along-strike extent of the gap between mantle and crus- tal earthquakes coincides with a zone of minimum convergence velocity identified in GPS measurements ( Fig. 2; e.g., ...
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... northeast-dipping plane of seismicity has an apparent dip of $ 40 and a maximum depth that decreases eastwards (Figs. 2, S5 and Movie S1). At the western end of the zone of seismicity, there is a discontinuity in seismicity down dip, with a lack of $50 km deep events (see profiles B-B 0 and X-X 0 in Fig. 2). While there are other partial gaps in seismicity, this is the largest contin- uous aseismic region in the dipping zone of seismicity, continuing for $100 km along strike (X-X 0 in Fig. 2) and up to $50 km down dip (B-B 0 and X-X 0 in Fig. 2). As with the maximum earthquake depths, the width of the discontinuity also decreases eastwards (from position 350 to 450 km on profile X-X 0 in Fig. 2) until the zone of deep earthquakes eventually merges with those in the crust. The along-strike extent of the gap between mantle and crus- tal earthquakes coincides with a zone of minimum convergence velocity identified in GPS measurements ( Fig. 2; e.g., ...
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... northeast-dipping plane of seismicity has an apparent dip of $ 40 and a maximum depth that decreases eastwards (Figs. 2, S5 and Movie S1). At the western end of the zone of seismicity, there is a discontinuity in seismicity down dip, with a lack of $50 km deep events (see profiles B-B 0 and X-X 0 in Fig. 2). While there are other partial gaps in seismicity, this is the largest contin- uous aseismic region in the dipping zone of seismicity, continuing for $100 km along strike (X-X 0 in Fig. 2) and up to $50 km down dip (B-B 0 and X-X 0 in Fig. 2). As with the maximum earthquake depths, the width of the discontinuity also decreases eastwards (from position 350 to 450 km on profile X-X 0 in Fig. 2) until the zone of deep earthquakes eventually merges with those in the crust. The along-strike extent of the gap between mantle and crus- tal earthquakes coincides with a zone of minimum convergence velocity identified in GPS measurements ( Fig. 2; e.g., ...
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... northeast-dipping plane of seismicity has an apparent dip of $ 40 and a maximum depth that decreases eastwards (Figs. 2, S5 and Movie S1). At the western end of the zone of seismicity, there is a discontinuity in seismicity down dip, with a lack of $50 km deep events (see profiles B-B 0 and X-X 0 in Fig. 2). While there are other partial gaps in seismicity, this is the largest contin- uous aseismic region in the dipping zone of seismicity, continuing for $100 km along strike (X-X 0 in Fig. 2) and up to $50 km down dip (B-B 0 and X-X 0 in Fig. 2). As with the maximum earthquake depths, the width of the discontinuity also decreases eastwards (from position 350 to 450 km on profile X-X 0 in Fig. 2) until the zone of deep earthquakes eventually merges with those in the crust. The along-strike extent of the gap between mantle and crus- tal earthquakes coincides with a zone of minimum convergence velocity identified in GPS measurements ( Fig. 2; e.g., ...
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... northeast-dipping plane of seismicity has an apparent dip of $ 40 and a maximum depth that decreases eastwards (Figs. 2, S5 and Movie S1). At the western end of the zone of seismicity, there is a discontinuity in seismicity down dip, with a lack of $50 km deep events (see profiles B-B 0 and X-X 0 in Fig. 2). While there are other partial gaps in seismicity, this is the largest contin- uous aseismic region in the dipping zone of seismicity, continuing for $100 km along strike (X-X 0 in Fig. 2) and up to $50 km down dip (B-B 0 and X-X 0 in Fig. 2). As with the maximum earthquake depths, the width of the discontinuity also decreases eastwards (from position 350 to 450 km on profile X-X 0 in Fig. 2) until the zone of deep earthquakes eventually merges with those in the crust. The along-strike extent of the gap between mantle and crus- tal earthquakes coincides with a zone of minimum convergence velocity identified in GPS measurements ( Fig. 2; e.g., ...
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... northeast-dipping plane of seismicity has an apparent dip of $ 40 and a maximum depth that decreases eastwards (Figs. 2, S5 and Movie S1). At the western end of the zone of seismicity, there is a discontinuity in seismicity down dip, with a lack of $50 km deep events (see profiles B-B 0 and X-X 0 in Fig. 2). While there are other partial gaps in seismicity, this is the largest contin- uous aseismic region in the dipping zone of seismicity, continuing for $100 km along strike (X-X 0 in Fig. 2) and up to $50 km down dip (B-B 0 and X-X 0 in Fig. 2). As with the maximum earthquake depths, the width of the discontinuity also decreases eastwards (from position 350 to 450 km on profile X-X 0 in Fig. 2) until the zone of deep earthquakes eventually merges with those in the crust. The along-strike extent of the gap between mantle and crus- tal earthquakes coincides with a zone of minimum convergence velocity identified in GPS measurements ( Fig. 2; e.g., ...
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... infer that the down-dip gap in seismicity in the region with the deepest earthquakes (Profiles B-B 0 and X-X 0 on Fig. 2) most likely represents a laterally propagating tear in the slab. The slab appears largely continuous farther to the east in our data (Profile C-C 0 on Fig. 2), constraining the width of this tear to <100 km along-strike. Such an eastward propagating tear in the slab explains both the local minima in convergence velocity coincident with the location of the tear and the eastward increase in conver- gence velocity along-strike (Profile X-X 0 on Fig. 2). Observations from both other orogens and geodynamic models indicate that convergence velocity immediately up-dip of a laterally propagating slab tear will be nearly zero because the remnant portion of the slab no longer feels the negative buoyancy of the deeper slab (e.g., [118]). Along-strike from a slab tear, the up-dip portion of the still-attached slab will exhibit a velocity gradient increasing away from the tip of the slab tear, identical to the pattern observed in the eastern Greater Caucasus (Profile X-X 0 on Fig. ...
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... infer that the down-dip gap in seismicity in the region with the deepest earthquakes (Profiles B-B 0 and X-X 0 on Fig. 2) most likely represents a laterally propagating tear in the slab. The slab appears largely continuous farther to the east in our data (Profile C-C 0 on Fig. 2), constraining the width of this tear to <100 km along-strike. Such an eastward propagating tear in the slab explains both the local minima in convergence velocity coincident with the location of the tear and the eastward increase in conver- gence velocity along-strike (Profile X-X 0 on Fig. 2). Observations from both other orogens and geodynamic models indicate that convergence velocity immediately up-dip of a laterally propagating slab tear will be nearly zero because the remnant portion of the slab no longer feels the negative buoyancy of the deeper slab (e.g., [118]). Along-strike from a slab tear, the up-dip portion of the still-attached slab will exhibit a velocity gradient increasing away from the tip of the slab tear, identical to the pattern observed in the eastern Greater Caucasus (Profile X-X 0 on Fig. ...
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... infer that the down-dip gap in seismicity in the region with the deepest earthquakes (Profiles B-B 0 and X-X 0 on Fig. 2) most likely represents a laterally propagating tear in the slab. The slab appears largely continuous farther to the east in our data (Profile C-C 0 on Fig. 2), constraining the width of this tear to <100 km along-strike. Such an eastward propagating tear in the slab explains both the local minima in convergence velocity coincident with the location of the tear and the eastward increase in conver- gence velocity along-strike (Profile X-X 0 on Fig. 2). Observations from both other orogens and geodynamic models indicate that convergence velocity immediately up-dip of a laterally propagating slab tear will be nearly zero because the remnant portion of the slab no longer feels the negative buoyancy of the deeper slab (e.g., [118]). Along-strike from a slab tear, the up-dip portion of the still-attached slab will exhibit a velocity gradient increasing away from the tip of the slab tear, identical to the pattern observed in the eastern Greater Caucasus (Profile X-X 0 on Fig. ...
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... infer that the down-dip gap in seismicity in the region with the deepest earthquakes (Profiles B-B 0 and X-X 0 on Fig. 2) most likely represents a laterally propagating tear in the slab. The slab appears largely continuous farther to the east in our data (Profile C-C 0 on Fig. 2), constraining the width of this tear to <100 km along-strike. Such an eastward propagating tear in the slab explains both the local minima in convergence velocity coincident with the location of the tear and the eastward increase in conver- gence velocity along-strike (Profile X-X 0 on Fig. 2). Observations from both other orogens and geodynamic models indicate that convergence velocity immediately up-dip of a laterally propagating slab tear will be nearly zero because the remnant portion of the slab no longer feels the negative buoyancy of the deeper slab (e.g., [118]). Along-strike from a slab tear, the up-dip portion of the still-attached slab will exhibit a velocity gradient increasing away from the tip of the slab tear, identical to the pattern observed in the eastern Greater Caucasus (Profile X-X 0 on Fig. ...
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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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... 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). ...
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By comparing the DMB with ACMS, we conclude:
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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.
