EVALUATING GNEISS DOME THERMAL EVOLUTION USING 2-D COUPLED THERMOMECHANICAL FINITE-ELEMENT MODELING

Gneiss domes in Tibet are a well-known feature of the Himalaya-Tibetan orogenic system, which resulted from continental collision of India and Asia beginning in the Eocene. These gneiss domes have been identified as features associated with syncollisional ductile extension and brittle normal slip occurring parallel to the South Tibetan detachment (STD) system. Structural, kinematic, and thermochronologic data collected from high-grade metamorphic and intrusive rocks; specifically, two gneiss domes located in Tibet: Mabja and Kangmar, exhibit patterns of increasing cooling age with increasing structural depth. Previous interpretations attribute this type of inverted temporal relationship to thermal histories that were affected by relatively cool overlying Tethyan sediments, but further evidence supporting this interpretation is lacking. Alternatively, new 2-D forward thermomechanical finite-element modeling of thrust emplacement yields heating distributions that are consistent with inverted metamorphic field gradients observed between the Main Central thrust and STD, and thus may also explain the thermal evolution of Tibetan gneiss domes (TGDs) and gneiss dome structures identified in other orogens (e.g. Tallulah Falls dome, southern Appalachians). To test the effect of advective heating due to mass transfer at relatively high thrust rates on TGD formation, kinematic and thermal boundary conditions from previous work are built in to new 2-D thermomechanical models. Results are compared with observed TGD thermochronologic data to determine the appropriateness of these models for explaining gneiss dome thermal evolution.