Testing Models of Cenozoic Exhumation in the Western Greater Caucasus.

Abstract

The Greater Caucasus form the northernmost deformation front of the Arabia‐Eurasia collision zone. Earlier thermochronometric studies on the crystalline core of the western Greater Caucasus highlighted an abrupt along‐strike increase in cooling ages to the west of Mt. Elbrus. Twenty‐eight thermochronometric analyses conducted as part of this study confirm this pattern. Overall Cenozoic exhumation was restricted to less than 5–7 km, with slow to moderate punctuated Oligo‐Miocene cooling. Cooling rates increased during the Late Miocene to Pliocene. These are most rapid east of Mt. Elbrus, where they probably increased later than farther west (at c. 5 Ma rather than 10–8 Ma). Differential cooling rates do not appear to be driven by lateral variations in tectonic shortening. The region undergoing rapid young cooling does coincide, however, with an area of mantle‐sourced Late Miocene and younger magmatism. Thermal relaxation or overprinting is ruled out because geomorphic and modern sediment flux data mirror the thermochronometric trends. The buoyancy effects of demonstrable mantle upwelling are capable of causing the magnitude of exhumation‐related cooling recorded in this study, but typically act over wavelengths of several 100 km. We suggest that lithospheric heterogeneities are responsible for modulating the shorter wavelength differences in exhumation rate documented here. These heterogeneities may include the continuation of the same structures responsible for the eastern margin of the Stavropol High to the north of the Caucasus, although further work is required. Similar abrupt variations in mantle‐supported uplift and exhumation modulated by crustal structure may occur in other mountain belts worldwide.