Effects of Wedge Disruption and South Caspian Subsidence on the Dynamic Stability of the Greater Caucasus Orogen
Abstract
The west-northwest trending Greater Caucasus Mountains form the northern margin of the Arabia-Eurasia collision between 40° and 50°E and appear to represent the main locus of shortening since the early Pliocene in this central part of the collision. Compared to similar mountain ranges, few detailed cross sections exist that extend across the whole range, but previous work suggests the first order structure of the Greater Caucasus comprises a bivergent wedge, with the southern and northern margins of the Greater Caucasus as pro- and retro-wedges respectively. However, it is apparent that the plan-view morphology, topography, and drainage networks of the Greater Caucasus do not neatly conform to many of the characteristics of an idealized bivergent wedge. We hypothesize that the along-strike deviations from such idealized geometries are the result of disruption of the Greater Caucasus wedge by collision with the Lesser Caucasus to the south, combined with efficient removal of material from the southeastern margin of Greater Caucasus and transport to the Kura and South Caspian basins, the latter of which contains ~10 km of post-Pliocene deposits. We further suggest that the simplest explanation for the current morphologic and topographic state of the Greater Caucasus is a transient response to these factors, indicating the range is not currently in steady state. In detail, the Greater Caucasus are underthrust from the south by a microplate in the Lesser Caucasus, producing dominantly south directed thrusts throughout the range and also, most recently, within the Kura fold-thrust belt along the SE margin of the orogen in Georgia and Azerbaijan, similar to the structural geometries expected in an ideal pro-wedge. The NE margin of the range also has well-developed north-directed thrust systems consistent with a retro-wedge. Yet, one of the hallmarks of bivergent wedges, a pronounced asymmetry between a wide pro- and narrow retro-wedge, is not observed in the Greater Caucasus. There is no dominant asymmetry consistent along-strike, but rather two distinct domains: a western one, in which the range is nearly symmetric, and an eastern one, where the pro- (southern) side is narrower than the north retro- side. The boundary between these domains is marked by the intersection of the Greater and Lesser Caucasus on the pro-side and a reentrant on the retro-side. The two domains also exhibit significant differences in various characteristics, including depth of exposure, position of the drainage divide relative to maximum topography, and presence or absence of flanking fold-thrust belts. We suggest that entrance of Lesser Caucasus material into the central and SW Greater Caucasus pro-wedge shifted the locus of deformation eastward, consistent with published GPS data indicating eastward-increasing rates of shortening within the eastern domain. Within the eastern pro-wedge we observe topographic, structural, and stratigraphic evidence of efficient removal of material from the wedge coeval with eastern propagation. We suggest that the rapid subsidence of the South Caspian basin provided accommodation space that enabled efficient removal of material from the SE pro-wedge and that the Greater Caucasus have not yet reached a steady state balance between these two competing factors.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.T13F2483F
- Keywords:
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- 8108 TECTONOPHYSICS / Continental tectonics: compressional;
- 8169 TECTONOPHYSICS / Sedimentary basin processes;
- 8175 TECTONOPHYSICS / Tectonics and landscape evolution