Constraints on the geologic processes and record of collision from an orogen currently transitioning from subduction to collision: the Greater Caucasus
Abstract
The timing of transition from subduction to collision in orogenic belts is inferred from the ages of proxies, including the onset of terrestrial sedimentation, dispersal of flora and fauna, sedimentary provenance, and collisional volcanism. Kinematic changes associated with this transition have also been inferred from thermochronometric and paleomagnetic data. Transition ages inferred from such proxies often differ, and there can therefore be uncertainty in linking these proxies to tectonic processes that accompany the initiation of collision. The Greater Caucasus (GC) mountain range in eastern Europe may present a unique opportunity to observe an incipient collisional orogen, potentially granting insight into the timing and spatial patterns of geologic processes associated with the initiation of collision.
The GC is a young orogen transitioning from subduction to collision diachronously along strike. The western GC is colliding with the adjacent Lesser Caucasus (LC), whereas the eastern GC is underlain by an actively subducting oceanic slab. Because the major structures and foreland deposits are exposed above sea level and much stratigraphic and seismic data exists for the range, the GC presents an excellent opportunity to characterize the spatial and temporal evolution of proxy records of collision. Here, we present new and previously published thermochronology data from the GC that constrain the exhumational response of the orogen to the onset of collision. Apatite (U-Th)/He and fission track ages from the western and eastern GC indicate a tenfold increase in exhumation rate (to 1 mm/yr) at 3-5 Ma, which we interpret as the result of collision. The ongoing subduction in the eastern GC means that the observed acceleration in exhumation precedes the end of subduction and slab detachment. In the GC, conglomeratic sedimentation precedes or coincides with rapid exhumation, and collisional volcanism follows removal of the subducting slab. We hypothesize that in the GC, the deposition of coarse sediment begins as the foreland basin between the two continents becomes small, then exhumation rates increase when initial collision occurs, and finally subduction ends and the slab detaches, driving volcanism. This hypothesized order of events may apply to other collisional orogens throughout geologic history.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T54A..04T
- Keywords:
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- 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 8038 Regional crustal structure;
- STRUCTURAL GEOLOGYDE: 8104 Continental margins: convergent;
- TECTONOPHYSICSDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS