Paper No. 6
Presentation Time: 3:10 PM


FORTE, Adam M.1, COWGILL, Eric1 and NIEMI, Nathan2, (1)Department of Geology, University of California, One Shields Avenue, Davis, CA 95616, (2)Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109,

The west-northwest trending Greater Caucasus (GC) form the northern margin of the Arabia-Eurasia collision between 40° and 50° E and represent the main locus of shortening since early Pliocene in this part of the orogen. Although new thermochronologic results constrain initiation of orogeny, the first-order structural geometry and kinematic evolution of this young orogen remain enigmatic. To address these problems, we report new provenance data, including sandstone point counts, trace element geochemistry, and U-Th-Pb analyses of detrital zircons (DZ) from modern river sediments, GC bedrock, and Mio-Pleistocene deposits from the Kura Foreland Basin, southeast of the GC. These analyses indicate a previously unrecognized suture may exist within the GC that potentially accommodated significant (>500 km) Cenozoic shortening during closure of a former back-arc basin in the GC. The provenance data also suggest Pleistocene structural reorganization within the GC, likely due to collision of the southern GC orogenic wedge with the Lesser Caucasus (LC) block. In detail, samples from within the GC reveal two distinct source terranes, a southern, late Mesozoic, volcanic and volcaniclastic terrane geochemically and chronologically indistinguishable from the northern LC, and a northern, geochemically evolved terrane containing early Mesozoic and Paleozoic DZ ages. Presently, these two terranes are separated by tens of kilometers, but the lack of overlap in their DZ signatures indicate initial deposition in a basin sufficiently large to separate the two sources. The provenance of Kura Basin sediments suggests initial sourcing from the southern GC volcanic source, and then replacement of this source upsection by the northern GC source. This provenance shift precedes a drainage reorganization in the GC during which catchment areas of south flowing GC rivers were drastically reduced via formation of a new, more southern drainage divide and capture of the rivers headwaters by north flowing GC rivers. We hypothesize that the shift in provenance and drainage reorganization were driven by the southern propagation of the GC range front. This resulted in uplift and exhumation of LC-affinity arc rocks, and in the beheading of GC rivers. These results highlight the potential for detrital records to elucidate major orogenic events.