Collaborative Research: A Structural, Thermochronologic, and Provenance Investigation of a Hypothesized Transition From Subduction to Slab Breakoff in the Greater Caucasus

University Of California-Davis, Davis CA

Investigators

Abstract

Slab breakoff, in which a slab detaches from a subducting plate and sinks into the mantle, exerts a first-order control on the geodynamic evolution of collisional orogenic belts because breakoff fundamentally alters the forces along the convergent margin. Modeling indicates that observable characteristics of breakoff within a collisional orogen include subduction of an ocean basin before collision, a transient pulse of accelerated rock and surface uplift in the belt, a decrease in convergence rate over the breakoff and an increase above adjacent parts of the slab that remain attached. However, geologic observations of this process within continental collision zones are not well documented. This University of California Davis and University of Michigan research team, in collaboration with their international partners, in explores the idea that the recent geological history of the Greater Caucasus (between the Black Sea and the Caspian Sea) is a consequence of this process. The project will advance desired societal outcomes by: (1) development of a globally competitive STEM workforce through the training of several U.S. graduate students, involvement of undergraduate students in research, and training of graduate students from Georgia, Armenia, and Azerbaijan; (2) increased partnerships between academia and the hydrocarbon industry and strengthening of existing collaborations and the development of new collaborations with scientists in Armenia and Georgia, Taiwan, and Canada. The project would provide the graduate students with rich international research experiences. The project is supported by the Tectonics Program and NSF's International Science and Engineering program. This research project will test the hypothesis that the Greater Caucasus reflects the transient geodynamic response to recent slab breakoff beneath the western portion of the range. This event follows the Oligocene to Pliocene closure of a remnant ocean basin, subduction of which presently continues beneath the eastern half of the range. The research team will carry out a field investigation of this little-studied orogen using structural mapping and balanced cross-sections, sediment provenance studies using U-Pb analyses of detrital zircons and (U-Th)/He analyses of apatite, bedrock low-temperature thermochronometry, and neotectonic investigations. They aim to constrain the magnitude of Cenozoic shortening across the Greater Caucasus along three orogen-perpendicular sections, and to derive the exhumation history of the Greater and Lesser Caucasus from low-temperature thermochronometry. Integration of these data with detrital provenance and lag time analyses of adjacent sedimentary basins will capture the geologic response to a transient geodynamic event and record perhaps the first evidence for slab detachment at the subduction-to-collision transition in an active orogen.