Rates of Thermal and Structural Processes in an Oblique Orogen

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

0106667 Whitney Crustal thickening and exhumation in highly oblique (wrench) tectonic settings typify large regions of the Himalayas, Alps, North American Cordillera, and other mountain systems, but the thermal and structural effects of oblique motion on mid- to deep crustal levels of orogens are poorly known. Simple thermal models predict that oblique zones will experience prolonged heating and delayed unroofing relative to more head-on convergent zones. Unresolved questions related to this model and its application to orogens include: What are the rates and styles of thermal and structural processes during oblique deformation at different crustal levels? How does the style and timing of deformation change from the mid- to upper crust in zones of oblique deformation? The Anatolian segment of the Alpine-Himalayan orogen contains both obliquely deformed and head-on deformed zones that record the interplay between crustal deformation and metamorphism. In central Anatolia, mid-crustal rocks were unroofed by extension during transpression and transtension in a broad zone of shearing, with the upper crustal lid preserved in an adjacent sedimentary basin. The Nigde core complex in central Anatolia provides a window into the mid-crust of a highly oblique orogenic system and permits reconstruction of the tectonic and thermal history of the upper 20 km of continental crust during oblique motion. As part of the overall study of the thermal and structural evolution of oblique orogens, ideas about wrench tectonic zones are tested using the following methods: Fieldwork to determine the distribution of rock types and structures in the context of metamorphic facies, and to collect samples for kinematic and isotopic analyses; Structural and kinematic studies to reconstruct the deformation history of different levels of the mid- to upper crust; High-temperature geochronology (U-Pb) and thermochronology (40Ar-39Ar; fission track) to determine the timing of peak metamorphism and cooling histories of various crustal levels. These data are used to determine the duration of metamorphism, timing of magmatic, metamorphic, and tectonic events, and to infer exhumation rates/mechanisms.