Assessing the Roles of Tectonics and Climate in Building Up and Breaking Down the Greater Caucasus Mountains: A Combined Analysis of Topography, Hydroclimate, Detrital Zircon (U-Th)/He, and 10Be Erosion Rate Data
Résumé
The Greater Caucasus (GC) mountains, a young (5-10 million years old) actively deforming mountain range within the central Arabia-Eurasia collision, are an interesting location to examine interplays between tectonics and climatically mediated surface processes. Currently, the range experiences an along-strike, order of magnitude eastward increase in convergence rate and decrease in precipitation, but has remarkably similar topography. Previous work suggests a role for either dynamic topography driven by slab detachment beneath the slowly-converging and wet western GC or dramatically different long-term convergence histories along-strike. However, other work has found no clear relation between climate proxies and the topography or tectonics of the GC, contrasting with expectations for strong climate-tectonics coupling. Assessing these hypotheses has proven challenging given the lack of millennial scale erosion rates or spatially consistent thermochronology datasets, with the latter data being almost exclusively located in the western GC. We have addressed these deficiencies with new datasets collected along-strike, consisting of 34 catchment averaged 10Be erosion rates and 623 single grain, doubly dated U-Pb and (U-Th)/He ages from zircons extracted from 7 of the 10Be catchments. We integrate these new data with detailed analyses of the hydroclimatic setting of the GC from modern streamflow records, topography, and recently published long-term regional plate motion reconstructions. We find that millennial scale erosion rates largely mirror decadal scale convergence rates. However, longer-term rates of cooling or implied rates of exhumation are remarkably consistent along-strike, implying that modern convergence rates do not reflect long-term rates. Neither the millennial or long-term rates of erosion or cooling are consistent with a contribution to rock uplift from slab detachment. Instead, exhumation rates and topography are well explained by a simple model of orogenic growth driven by long-term convergence from plate models. Finally, the insensitivity of topography and tectonics to precipitation seems related to the sublinear nature of the topography-erosion rate relationship, likely driven by the importance of snowmelt hydrology in driving low daily stream runoff variability.