A field test of the rolling hinge model: Example from the Lunggar extensional system

The north-trending Lunggar Range is located in the west-central Lhasa terrane of the Tibetan Plateau. It is approximately 70 km long north-south and 40 km wide east-west. The Lunggar rift valley bounds the eastern margin of the range and is 5-10 km wide. The range bounding Lunggar detachment fault is an east-dipping, low-angle (<40°) normal fault, juxtaposing Miocene mylonites and granites against Paleogene (?) strata in the hanging wall. The Lunggar detachment is currently inactive based on field observations of alluvial fans and glacial moraines that unconformably overly it. Rift basin sediments are cut by moderately dipping antithetic and synthetic brittle normal faults that are capped by a cobble to boulder conglomerates. The active locus of extension is approximately 4-6 km into the hangingwall basin, which is defined by fault scarps with up to 40-50m of vertical throw. Previous field mapping and preliminary thermochronological results suggest that this progressive basinward stepping of normal faulting represents an evolving low-angle detachment system that began as a high angle normal fault. We will present new thermochronological samples collected from vertical transects across the footwall and hanging wall that will provide means to investigate the thermal history of the Lunggar detachment. The Lunggar detachment may serve as a natural laboratory for testing multiple aspects of large magnitude extensional tectonics and modern core-complex development.