Exhumational history of the north central Pamir

The Pamir plateau forms a prominent tectonic salient along the western end of the Tibet-Tarim margin. Despite its tectonic significance, relatively little is known about the timing of major Cenozoic tectonic events in the Pamir. Here we present new apatite and zircon (U/Th)-He ages, bulk rock geochemistry, and Al-in-hornblende barometry results from the Karakul graben, a prominent north-south oriented rift basin located similar to 50 km south of the Main Pamir Thrust. Although cooling ages do not record the onset of extension, graben-bounding normal faults provide exposures of otherwise slowly eroding rocks which record two Cenozoic thermal events. Existing geochronology and new results suggest that granitic rocks in the Karakul region were shallowly emplaced, cooled very quickly through similar to 300 degrees C, and have experienced less than 10 km of exhumation since the late Triassic. A long period of relatively slow exhumation throughout much of the late Mesozoic and Cenozoic was punctuated by two periods of accelerated exhumation during the middle Eocene (similar to 50-40 Ma) and early Miocene (similar to 25-16 Ma). We interpret the first period of accelerated exhumation as a result of tectonic uplift and subsequent erosion due to the northward propagation of the India-Asia collision. We attribute the second period of rapid exhumation to a renewed phase of tectonism and plateau uplift in the Pamir, perhaps related to a break off event along the down-going Indian plate at similar to 25 Ma or to the onset of slip along the nascent Karakoram fault. Citation: Amidon, W. H., and S. A. Hynek (2010), Exhumational history of the north central Pamir, Tectonics, 29, TC5015, doi: 10.1029/2009TC002589.