October 2015
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66 Reads
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Publications (3)
![Fig. 1. (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.)](https://www.researchgate.net/profile/Nathan-Niemi/publication/269391445/figure/fig1/AS:613971778342922@1523393687684/a-Location-of-Arabia-Eurasia-collision-zone-within-the-Alpine-Himalayan-belt-GC_Q320.jpg)
![Fig. 2. 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.)](https://www.researchgate.net/profile/Nathan-Niemi/publication/269391445/figure/fig2/AS:613971778359355@1523393687909/Swath-profiles-of-earthquake-hypocenters-and-topography-refer-to-Fig-1c-for-profile_Q320.jpg)
![Fig. 3. 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.)](https://www.researchgate.net/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)
![Fig. 4. (a) Major tectonic features of the Greater Caucasus. Arrows are GPS velocity vectors relative to stable 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 semitransparent 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.)](https://www.researchgate.net/profile/Nathan-Niemi/publication/269391445/figure/fig4/AS:613971778363397@1523393687993/a-Major-tectonic-features-of-the-Greater-Caucasus-Arrows-are-GPS-velocity-vectors_Q320.jpg)
March 2015
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1,513 Reads
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78 Citations
GeoResJ
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, and Azerbaijan, together with previously published hypocenter locations, we show that the central and eastern Greater Caucasus Mountains are underlain by a northeast-dipping zone of mantle seismicity that we interpret as a subducted slab. Beneath the central Greater Caucasus (east of 45°E), the zone of seismicity extends to a depth of at least 158 km with a dip of ∼40°NE and a slab length of ∼130–280 km. In contrast, beneath the western GC (west of 45°E) there is a pronounced lack of events below ∼50 km, which we infer to reflect slab breakoff and detachment. We also observe a gap in intermediate-depth seismicity (45–75 km) at the western end of the subducted slab beneath the central Greater Caucasus, which we interpret as an eastward-propagating tear. This tear coincides with a region of minimum horizontal convergence rates between the Lesser and Greater Caucasus, as expected in a region of active slab breakoff. Active subduction beneath the eastern Greater Caucasus presents a potentially larger seismic hazard than previously recognized and may explain historical records of large magnitude (M 8) seismicity in this region.
December 2014
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70 Reads
Citations (1)
... 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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March 2015
GeoResJ