triangular facet Large garnet porphyroblast with an internal foliation of quartz and opaque inclusion trails defining a S1 foliation crenulated by a S2 foliation. S2 foliation wraps around garnet. Kangmar Dome, Tibet triangular facet Core of the Gianbul Dome, India.

Middle Crustal Flow and Tectonic Evolution of Gneiss Domes & Metamorphic Core Complexes
Project Summary

Gneiss domes are found in orogenic belts worldwide and are typically composed of a core of middle crustal rocks, including granitic migmatites or gneisses, structurally overlain by a mantle of high-grade metasedimentary rocks which in turn are overlain by unmetamorphosed rocks. A number of mechanisms have been proposed for the origin of gneiss domes, ranging from diapirism, crustal shortening, and crustal extension, to some combination of these processes. Each of these mechanisms, or combinations thereof, have dramatically different implications for the tectonic evolution of an orogen.

The North Himalayan gneiss domes, southern Tibet are a series of isolated domes that provide a window into the middle crust within the Tethyan Himalaya south of the Indus-Tsangpo Suture Zone and north of the Southern Tibetan detachment system. Our research on these domes is an integrated (geologic mapping, structural and kinematic analyses, metamorphic petrology, thermochronology, and geochronology) investigation of the processes of ductile flow in the middle crust of southern Tibet, of the mechanisms by which these gneiss domes formed and were exhumed, and the implications of those mechanisms for the tectonic and geodynamic evolution of the India-Asia collision. A similar project is ongoing on Gianbul Dome, northwest India. This dome, in contrast to the North Himalayan gneiss domes, is exposed in the footwall of the Zanskar shear zone, the western exposure of the Southern Tibetan detachment system. Like the North Himalayan gneiss domes, our research goals are to document the mechanisms by which this gneiss dome formed and was exhumed, and the implications of those mechanisms for the tectonic and geodynamic evolution of northwestern part of the India-Asia collision.

Metamorphic core complexes in the western U.S. record a complex history of ductile and brittle extensional deformation associated with metamorphism and magmatism, and final exhumation within the footwalls of high-angle Basin and Range normal faults. Core complexes are characterized by a domal geometry and a low-angle, normal slip detachment fault that juxtaposes a hanging wall of generally unmetamorphosed upper crustal sedimentary and volcanic rocks cut by high-angle normal faults from a footwall of ductilely extended middle crustal metasedimentary and metaigneous rocks. Although the structural, metamorphic, intrusive, and exhumation histories and tectonic significance of metamorphic core complexes have been topics of research for more than 40 years, there remains disagreement about detachment fault formation mechanisms, whether brittle and ductile extensional deformation are spatially and temporally linked, and the geodynamic processes that drive their formation. Our research uses a combination of geologic mapping, structural and kinematic studies, geochronology, and thermochronology to address these issues.

Publications on Gneiss Domes in Tibet and NW India (* = student author) Publications on Metamorphic Core Complexes (* = student author)