Relict Basin Closure Inferred from Detrital Zircon Provenance in the Caucasus: A Solution to Missing Arabia-Eurasia Convergence?

Eric Cowgill, Univ. California, Davis
Adam Forte, Arizona State University
Nathan Niemi, Univ. of Michigan
Mikheil Elashvili, Ilia State University, Tbilisi, Georgia
Tea Godoladze, Ilia State University, Tbilisi, Georgia

Comparison of total plate convergence with the timing and magnitude of upper crustal shortening in active collisional orogens has consistently revealed both large shortening deficits (200 to 1700 km) and significant (30-40%) deceleration of plate motion during progressive collision, the cause(s) for which remain intensely debated. The Greater Caucasus Mountains, which result from post-collisional Cenozoic closure of a relict Mesozoic back-arc basin on the northern margin of the Arabia-Eurasia collision zone, may help reconcile these debates. Here we use U-Pb detrital zircon provenance data and the regional geology of the Caucasus to investigate the width of the now-consumed Mesozoic back-arc basin and its closure history. The provenance data record distinct southern and northern provenance domains that persist in the sedimentary record until at least the Miocene. We propose that closure of the back-arc basin initiated at ~35 Ma, coincident with initial (soft) Arabia-Eurasia collision along the Bitlis suture, and eventually led to ~5 Ma (hard) collision between the Lesser Caucasus arc to the south and Variscan basement along the margin of the Scythian platform to the north to form the Greater Caucasus Mountains. Final basin closure triggered deceleration of plate convergence and tectonic reorganization throughout the collision zone as a whole. We find that post-collisional subduction of such relict ocean basins can both account for shortening deficits, by accommodating convergence with minimal upper crustal shortening, and significantly delay deceleration of plate convergence. Such relict basin closure is likely typical of the early phases of continental collision at the end of a Wilson cycle due to both the irregular nature of colliding continental margins and their propensity to develop extensive back-arc basins during protracted subduction and terrane accretion prior to closure of long-lived ocean basins.


Localization processes within the lithosphere