When Neither Climate or Tectonics Appear Related to Topography, Erosion, and Rock Uplift Rates: The Curious Case of the Greater Caucasus Mountains
Abstract
The Greater Caucasus (GC) mountains, stretching from the Black to the Caspian sea, are a young (~5 Ma), active orogenic system that is the current locus of NE-SW convergence within the central Arabia-Eurasia collision zone. The GC are characterized by a variety of NW-SE, along-strike gradients including an order of magnitude eastward decrease in mean annual precipitation from ~2 to ~0.5 m/yr and an order of magnitude eastward increase in geodetic shortening velocity from ~2 to ~12 mm/yr. Despite these gradients, the topography of the range is surprisingly similar along-strike which suggests: (1) broadly similar rates of rock uplift, and (2) very limited influence of precipitation on the topography of the range. However, this hypothesis is predicated on the existence of a single relationship between topography and uplift/erosion rate. Here we test this assumption with a new suite of erosion rates estimated from catchment averaged 10Be inventories along the southern range front of the GC. Erosion rates range from 30-5600 m/Myr with the majority of rates being below 2000 m/Myr. Our results are consistent with a single relationship between erosion rate and topography as quantified by normalized channel steepness (ksn). These data also indicate a strongly non-linear relationship between ksn and erosion rate such that topography seems insensitive to increases in erosion rate beyond ~500 m/Myr. There is limited evidence of any influence of mean precipitation on either the topography or the erosion rates of the GC. We hypothesize that this lack of sensitivity to mean precipitation and the related non-linearity in the ksn - erosion rate relationship may be linked to the extremely low variability in runoff observed in gauged basins throughout the region. Spatial patterns in 10Be erosion rates largely mirror those observed in a suite of available bedrock low-temperature thermochronologic cooling ages, i.e. areas with high erosion rates generally have young cooling ages. This is consistent with prior suggestions that either the modern shortening rates are not indicative of long-term tectonic forcing or that there is an additional source of rock uplift, though our results do not allow us to discriminate between those two options.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMEP31C2277F
- Keywords:
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- 1815 Erosion;
- HYDROLOGY;
- 1824 Geomorphology: general;
- HYDROLOGY;
- 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS;
- 8177 Tectonics and climatic interactions;
- TECTONOPHYSICS