DETRITAL ZIRCON GEOCHRONOLOGY OF THE PALEOZOIC TO PALEOGENE STRATA OF THE CENTRAL PAMIR UPPER CRUST

Extensive recent research on metamorphic domes of the Pamir Range, Tajikistan have provided rich insight into the nature of the middle to lower crust of the orogen prior to gravitational collapse. The character and provenance of the sedimentary upper crust, however, has received relatively little attention, especially in Central Pamir. Integration of new geologic mapping, detrital zircon U-Pb geochronology (n=3512), and sedimentary and metamorphic petrography of the hanging wall of the Muskol metamorphic dome (~38.3°N, ~74.1°E) provides new constraints on the evolution of the orogen from Triassic to late Oligocene time. Using geochronologic data compiled from existing literature for the Pamir and Tibetan Plateau, we compare the detrital signatures of the sedimentary record of the Central Pamir to that of the Songpan-Ganzi and Qiangtang terranes in Tibet to correlate major terranes and sutures across the orogen, and to evaluate the continuity of major tectonic processes along-strike, including large-scale sedimentation in the Paleotethys ocean, the amalgamation of crustal fragments following the subduction and eventual closure of the Paleotethys ocean, as well as various episodes of magmatism associated with both convergence and extension in the orogen. Specifically, we document the southernmost extent of the Triassic Karakul-Mazar or Songpan-Ganzi equivalent strata in Pamir, along with exposures of accretionary mélange that contain exotic blocks of carbonate and mafic cumulate, interpreted to be associated with the subduction of the Paleotethys ocean. The Triassic rocks are unconformably overlain in some localities by lower- to mid-Cretaceous volcaniclastic sandstones and metavolcanics, and upper-Cretaceous (ca. 80 Ma) syn-rift conglomerates, red beds, and basalt flows, providing evidence for extensional tectonics in the orogen at this time. Elsewhere, the Triassic strata are overlain by Oligocene or younger conglomerates and sandstones that record an episode of magmatism at 34-30 Ma, which is absent in the extant rock record in the Pamir but overlaps in age with ultrapotassic volcanic rocks in the Qiangtang terrane to the southeast. Overall, the Triassic to Cenozoic stratigraphy and mélanges of the Central Pamir can be correlated in part with both the Songpan-Ganzi and Qiangtang terranes in Tibet.