Building a Young Mountain Range: Insight into the Growth of the Greater
Caucasus Mountains from Detrital Zircon (U-Th)/He Thermochronology and
10Be Erosion Rates
Abstract
The Greater Caucasus (GC) Mountains within the central Arabia-Eurasia
collision zone, are an archetypal example of a young collisional orogen.
However, the mechanisms driving rock uplift and forming the topography
of the range are controversial, with recent provocative suggestions that
uplift of the western GC is strongly influenced by an isostatic response
to slab detachment, whereas the eastern half has grown through
shortening and crustal thickening. Testing this hypothesis is
challenging because records of exhumation rates mostly come from the
western GC, where slab detachment may have occurred. To address this
data gap, we report 623 new, paired zircon U-Pb and (U-Th)/He ages from
7 different modern river sediments, spanning a ~400 km
long gap in bedrock thermochronometer data. We synthesize these with
prior bedrock thermochronometer data, recent catchment averaged 10Be
cosmogenic exhumation rates, topographic analyses, structural
observations, and plate reconstructions to evaluate the mechanisms
growing the GC topography. We find no evidence of major differences in
rates, timing of onset of cooling, or total amounts of exhumation across
the possible slab edge, inconsistent with previous suggestions of
heterogeneous drivers for exhumation along-strike. Comparison of
exhumation across timescales highlight a potential acceleration, but one
that appears to suggest a consistent northward shift of the locus of
more rapid exhumation. Integration of these new datasets with simple
models of orogenic growth suggest that the gross topography of the GC is
explainable with traditional models of accretion, thickening, and uplift
and does not require any additional slab-related mechanisms.