Exploring the transition from subduction to slab breakoff: Structural insights from the western Greater Caucasus Mountains

Chad Trexler

USGS Earthquake Science Center

Date & Time
Online-only seminar via Microsoft Teams

The Greater Caucasus Mountains, located between the Black and Caspian Seas at the northern margin of the Arabia-Eurasia collision zone, presently accommodate most (70%) of the orogen-perpendicular shortening within this sector of the collision zone. Patterns in exhumation, geodetic shortening rate, and subcrustal seismicity have led to the hypothesis that the modern range records an along-strike transition from an attached subducted slab in the east to a detached slab in the west.
To test this hypothesis, we combine 1:100k structural mapping along two orogen-perpendicular transects with stratigraphic and structural analyses to constrain the magnitude of shortening accommodated within the Greater Caucasus. Using these data, we construct balanced cross sections that accommodated ~200km of shortening across the orogen. In addition, we determine the modern geologic shortening rate across the active frontal thrust (~1.1 +/-0.5 mm/yr), providing a point of comparison with both geodetic rates across the full orogen at the same longitude (3-4 mm/yr) and longer term shortening rate estimates based on low-tempertature thermochronology (6-8 mm/yr).
In combination, these results are compatible with the slab detachment model of orogen evolution, and are not as consistent with other competing hypotheses. Though more work is needed, these data suggest that the Greater Caucasus may capture the surface expression of ongoing processes associated with the transition from subduction to continental collision.

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