Reply to Comment by Vincent et al.

Cowgill, Eric; Niemi, Nathan A.; Forte, Adam M.; Trexler, Charles C.

doi:10.1002/2017tc004793

Cited by 17 publications

(25 citation statements)

References 49 publications

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“…In the Kazbegi region of Georgia (Figure ), several early studies place the MCT along the Adaykom‐Kazbek (or Adaykomskiy) fault, which broadly juxtaposes the crystalline Gveleti and Dariali massifs to the north against Caucasus Basin strata to the south (Leonov, ; Shempelev, ), whereas other studies place the MCT on the Tiba fault ~20 km to the south (e.g., Rogozhin et al, ; Vincent et al, ). Likewise, the location of the MCT is also disputed within the Caucasus Basin strata in eastern Greater Caucasus, with some authors placing it within the main range (e.g., Mosar et al, ; Vincent et al, ) and others on the Zangi fault farther to the south, at a major structural juxtaposition of differing Cretaceous facies (Cowgill et al, ; Forte et al, ; Khain et al, ; Kopp & Shcherba, ). In the western Greater Caucasus, the MCT footwall comprises either the Dizi series or Caucasus Basin strata, depending on location.…”

Section: Tectonic Settingmentioning

confidence: 99%

Evolution of the Greater Caucasus Basement and Formation of the Main Caucasus Thrust, Georgia

et al. 2020

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Along the northern margin of the Arabia-Eurasia collision zone in the western Greater Caucasus, the Main Caucasus Thrust (MCT) juxtaposes Paleozoic crystalline basement to the north against Mesozoic metasedimentary and volcaniclastic rocks to the south. The MCT is commonly assumed to be the trace of an active plate-boundary scale structure that accommodates Arabia-Eurasia convergence, but field data supporting this interpretation are equivocal. Here we investigate the deformation history of the rocks juxtaposed across the MCT in Georgia using field observations, microstructural analysis, U-Pb and 40 Ar/ 39 Ar geochronology, and 40 Ar/ 39 Ar and (U-Th)/He thermochronology. Zircon U-Pb analyses show that Greater Caucasus crystalline rocks formed in the Early Paleozoic on the margin of Gondwana. Low-pressure/temperature amphibolite-facies metamorphism of these metasedimentary rocks and associated plutonism likely took place during Carboniferous accretion onto the Laurussian margin, as indicated by igneous and metamorphic zircon U-Pb ages of~330-310 Ma. 40 Ar/ 39 Ar ages of~190-135 Ma from muscovite in a greenschist-facies shear zone indicate that the MCT likely developed during Mesozoic inversion and/or rifting of the Caucasus Basin. A Mesozoic 40 Ar/ 39 Ar biotite age with release spectra indicating partial resetting and Cenozoic (<40 Ma) apatite and zircon (U-Th)/He ages imply at least~5-8 km of Greater Caucasus basement exhumation since~10 Ma in response to Arabia-Eurasia collision. Cenozoic reactivation of the MCT may have accommodated a fraction of this exhumation. However, Cenozoic zircon (U-Th)/He ages in both the hanging wall and footwall of the MCT require partitioning a substantial component of this deformation onto structures to the south. Plain Language Summary Collisions between continents cause deformation of the Earth's crustand the uplift of large mountain ranges like the Himalayas. Large faults often form to accommodate this deformation and may help bring rocks once buried at great depths up to the surface of the Earth. The Greater Caucasus Mountains form the northernmost part of a zone of deformation due to the ongoing collision between the Arabian and Eurasian continents. The Main Caucasus Thrust (MCT) is a fault juxtaposing old igneous and metamorphic (crystalline) rocks against younger rocks that has often been assumed to be a major means of accommodating Arabia-Eurasia collision. This study examines the history of rocks along the MCT with a combination of field work, study of microscopic deformation in rocks, and dating of rock formation and cooling. The crystalline rocks were added to the margins of present-day Eurasia about 330-310 million years ago, and the MCT first formed about 190-135 million years ago. The MCT is likely at most one of many structures accommodating present-day Arabia-Eurasia collision.

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Section: Tectonic Settingmentioning

confidence: 99%

Evolution of the Greater Caucasus Basement and Formation of the Main Caucasus Thrust, Georgia

et al. 2020

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“…However, Vincent et al (2018) argued that at least within the western Greater Caucasus, sedimentological, provenance, and seismic data supports an earlier basin closure age in Early Oligocene. Cowgill et al (2018) suggested that the closure of the basin initiated at about 35 My ago and ended at about 5 My ago following the collision between the Lesser Caucasus and the Scythian platform to form the Greater Caucasus. The basic underlying assumption related to the collision is that the Greater Caucasus results from farfield transmission of tectonic stresses from the Bitlis-Zagros collision zone.…”

Section: Geology and Geodynamicsmentioning

confidence: 99%

Geodynamics, seismicity, and seismic hazards of the Caucasus

Ismail‐Zadeh

Adamia

Chabukiani

et al. 2020

Earth-Science Reviews

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Being a part of ongoing continental collision between the Arabian and Eurasian plates, the Caucasus region is a remarkable site of moderate to strong seismicity, where devastating earthquakes caused significant losses of lives and livelihood. In this article, we survey geology and geodynamics of the Caucasus and its surroundings; magmatism and heat flow; active tectonics and tectonic stresses caused by the collision and shortening; gravity and density models; and overview recent geodetic studies related to regional movements. The tectonic development of the Caucasus region in the Mesozoic-Cenozoic times as well as the underlying dynamics controlling its development are complicated processes. It is clear that the collision is responsible for a topographic uplift / inversion and for the formation of the fold-and-thrust belts of the Greater and Lesser Caucasus. Tectonic deformations in the region is influenced by the wedge-shaped rigid Arabian block indenting into the relatively mobile region and producing near N-S compressional stress and seismicity in the Caucasus. Regional seismicity is analysed with an attention to sub-crustal seismicity under the northern foothills of the Greater Caucasus, which origin is unclearwhether the seismicity associated with a descending oceanic crust or thinned continental crust. Recent seismic tomography studies are in favour of the detachment of a lithospheric root beneath the Lesser and Greater Caucasus. The knowledge of geodynamics, seismicity, and stress regime in the Caucasus region assists in an assessment of seismic hazard and risk. We look finally at existing gaps in the current knowledge and identify the problems, which may improve our understanding of the regional evolution, active tectonics, geodynamics, shallow and deeper seismicity, and surface manifestations of the lithosphere dynamics. Among the gaps are those related to uncertainties in regional geodynamic and tectonic evolution (e.g., continental collision and associated shortening and exhumation, lithosphere structure, deformation and strain-stress partitioning) and to the lack of comprehensive datasets (e.g., regional seismic catalogues, seismic, gravity and geodetic surveys).

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“…Vincent et al (2007), instead, related basin closure around the Eocene-Oligocene transition to the far-field effects of initial Arabia-Eurasia collision, with this process being unrelated to later Arabia-Eurasia reorganization. Further details of these contrasting hypotheses can be found in the papers cited above and the ensuing correspondence (Cowgill et al, 2018;Vincent et al, 2018). Shaded relief digital elevation model of the Arabia-Eurasia collision zone showing selected GPS-constrained motions relative to stable Eurasia, the occurrence of instrumentally recorded earthquakes (M ≥ 4.5) and a selected number of their focal mechanisms.…”

Section: Introductionmentioning

confidence: 99%

“…Vincent et al (), instead, related basin closure around the Eocene‐Oligocene transition to the far‐field effects of initial Arabia‐Eurasia collision, with this process being unrelated to later Arabia‐Eurasia reorganization. Further details of these contrasting hypotheses can be found in the papers cited above and the ensuing correspondence (Cowgill et al, ; Vincent et al, ).…”

Section: Introductionmentioning

confidence: 99%

Testing Models of Cenozoic Exhumation in the Western Greater Caucasus

Vincent¹,

Somin

Carter

et al. 2020

Tectonics

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• There is a marked lateral change in the Cenozoic cooling history of the crystalline core of the western Greater Caucasus • The region with young cooling ages (between Mt. Elbrus and Mt. Kazbek) coincides with an area of mantle-sourced Late Miocene and younger magmatism • If driven by buoyancy forces, cooling must be partitioned over short wavelengths by lithospheric heterogeneities Vincent et al.

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Reply to Comment by Vincent et al.

Cited by 17 publications

References 49 publications

Evolution of the Greater Caucasus Basement and Formation of the Main Caucasus Thrust, Georgia

Evolution of the Greater Caucasus Basement and Formation of the Main Caucasus Thrust, Georgia

Geodynamics, seismicity, and seismic hazards of the Caucasus

Testing Models of Cenozoic Exhumation in the Western Greater Caucasus

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