T292 From Oceanic Subduction to Inter-Continental Collision: Examples of Convergent Margin Processes in Non-Collisional and Collisional Settings

Wednesday, 25 September 2019
1:30 PM - 5:30 PM
Room 231ABC, North Building

RECONCILING ALONG-STRIKE GRADIENTS IN OROGENIC STRUCTURE, RATES OF SHORTENING, AND CLIMATE WITH UNIFORM RATES OF EROSION IN THE GREATER CAUCASUS

Paper number: T292-5
Program: Technical Sessions
Time: 2:30 PM – 2:45 PM

Authors

Abstract

The Greater Caucasus (GC) mountains, stretching from the Black to the Caspian sea, represent the northernmost extent and current locus of NE-SW convergence within the central Arabia-Eurasia collision zone. The GC broadly resulted from the inversion and partial subduction of a former back-arc basin, but the original geometry of this basin, the extent to which basin closure was accommodated with or without true subduction, the timing of the transition from subduction to collision, and the extent to which any and all of these varied along-strike all remain controversial. Much of this debate stems from apparent fundamental differences between the western and eastern GC, suggestive of very different histories and behaviors between these two regions. Specifically, the western GC are characterized by exposures of Variscan basement, no deep earthquakes reflecting the lack of a subducted slab, and a relatively simple set of active structures defining it as a single-sided, south-vergent orogenic wedge. In contrast, the eastern GC are dominated by deposits of Jurassic-Cretaceous flysch lacking exposures of basement, with deep earthquakes extending to ~160 km defining a north-dipping slab, and is a doubly-sided orogenic wedge, fringed with structurally complicated, active fold-thrust belts. Additionally, in the modern, the GC experience an order of magnitude eastward increase in geodetic shortening velocity from ~2 to ~12 mm/yr and an order of magnitude decrease in mean annual precipitation from ~2 to ~0.5 m/yr. Despite all of these gradients in both structure and apparent forcings, the topography of the GC is remarkably similar along-strike, suggesting on average, similar rates of rock uplift. Here we test this idea with a new body of erosion rates from catchment averaged 10Be inventories. From these, we find a single relationship between topography and erosion rates with little climatic influence, implying that despite all of the aforementioned gradients, rates of erosion, and thus potentially rock uplift, do not vary significantly along strike in the GC. This further suggests that the histories of the western and eastern GC cannot be considered in isolation and that any tectonic models developed to explain the GC must account for the similarity in rock uplift rates along-the range.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-337927

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