Two-step exhumation of Caucasian intraplate rifts: A proxy of sequential plate-margin collisional orogenies

Abstract

Intraplate structural deformation is diagnostic of tectonic stress regime changes linked to plate interactions and can result from superposed tectonic events whose single contributions are hardly distinguishable. In this paper, we present a set of integrated thermochronologic inverse models along a 140 km-long transect across the central Greater Caucasus and the adjacent Adjara-Trialeti fold-and-thrust belt of Georgia, two intraplate orogens produced by structural inversion of parallel continental rift zones located on the Eurasian plate. Our dataset allows to distinguish discrete and superposed deformation episodes and quantify their respective contributions to orogenic exhumation. The integration of (U-Th)/He analysis on apatite and zircon, fission-track analysis on apatite, and peak-temperature determinations (clay mineralogy, organic matter petrography, Raman spectroscopy) shows that structural inversion was punctuated by two incremental steps starting respectively in the latest Cretaceous and the mid-Miocene. Latest Cretaceous partial inversion of the Greater Caucasus is documented here for the first time and placed in a geographically wider context of coeval deformation. The two episodes of intraplate structural inversion, exhumation, and sediment generation are chronologically and physically correlated with docking of (i) the Anatolide-Tauride-Armenian terrane (Late Cretaceous - Paleocene) and (ii) Arabia (Miocene hard collision) against the southern Eurasian plate margin. Intraplate deformation in the Caucasian domain was triggered by far-field propagation of plate-margin collisional stress which focused preferentially along rheologically weak rift zones.

Keywords

• Intraplate deformation
• Far-field tectonics
• Greater Caucasus
• Structural reactivation
• Terrane accretion