Tectonic Evolution of the Southeast Pamir
Imrecke, Daniel B. 1984-
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This study investigates the Mesozoic and Cenozoic tectonic evolution of the Southeast Pamir. Part one of this study focuses on the Neogene tectonic evolution of the Waqia Valley southeast of the Miocene Muztaghata Gneiss Dome. The valley was previously proposed to be bound to the northeast by the active left-slip Karakax Fault, which predicts active shortening structures and strike-slip separation in the valley. To test this model, geologic field mapping of sedimentary and basement units was conducted. The Waqia Valley is bound to the north and northeast by the Shen-Ti and Waqia Faults, which show extensional kinematics. Two distinct generations of sedimentary deposits occur in the valley: 1) Neogene deposits, which are up to ~1000 m thick, are cut by normal faults, onlap paleo-topography of basement units, and are in fault-contact with the Waqia Fault, and 2) undeformed Quaternary deposits which onlap previously eroded Neogene deposits. The absence of shortening or left-lateral strike slip structures or Quaternary deformation in the Waqia valley indicates the Karakax Fault does not project into the study area. Rather, the Waqia Valley basin formed by extension along the propagating tip of the Shen-Ti/Waqia Fault in the hanging wall of the Muztaghata Gneiss Dome. Part two of this study evaluates the Mesozoic deformation history and terrane architecture of the southeast Pamir. Structural field mapping of metasedimentary and igneous units in the study area, metamorphic petrology, garnet-biotite thermometry, and zircon U/Pb isotopic analysis were used to define and compare structural units north and south of the Muztaghata Gneiss Dome. North of Muztaghata, the Baoziya Thrust juxtaposes Triassic age amphibolite facies schists and gneisses with Triassic granites structurally above greenschist facies metasediments. South of the dome, the synformal Torbashi Thrust juxtaposes Triassic age amphibolite facies schists and gneisses with Triassic granites structurally above footwall greenschist facies metasediments. Based on these similarities, I propose the Baoziya and Torbashi Thrust previously formed a continuous thrust nappe prior to being cut by exhumation of the Muztaghata dome. In the southern footwall of the Torbashi Thrust, greenschist facies Metasediments intruded by Ordovician granites lie structurally above low-grade Paleozoic metasediments of Gondwanan affinity. The juxtaposition of Gondwanan rocks to the south, against units of Asian affinity to the north, implies the presence of a suture through the study area and provide new constraints on the geometry and deflection of terranes across the western Tibetan Orogen.