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New U-(Th)/Pb geochronology and geochemical analyses of plutonic bodies in the Hindu Kush range, NW Pakistan, provide insight on the crustal growth and tectonic evolution of the southern Eurasian margin. These new data outline a protracted magmatic history that spans the Cambrian to the Neogene (ca. 538 to 23 Ma) and record a variety of petrogenetic associations variably influenced by within plate, volcanic arc, and collision tectonic environments. The Kafiristan pluton (538 ± 4 to 487 ± 3 Ma) yields geochemical signatures consistent with extensional plutonism and rifting of the Hindu Kush terrane from Gondwana. The Tirich Mir (127 ± 1 to 123 ± 1 Ma) and Buni-Zom (110 ± 1 to 104 ± 1 Ma) plutons have geochemical signatures that can be attributed to a subduction related continental volcanic arc system that developed along the southern margin of Eurasia in the Mesozoic. The Garam Chasma pluton, the youngest body in the study area (27.3 ± 0.5 to 22.8 ± 0.4 Ma), yields a geochemical signature consistent with widespread anatexis during crustal thickening related to the development of the Himalaya. The present geochemical and geochronological analysis from the Hindu Kush have produced important new constraints on the timing of tectonic events and variable tectonic settings along the south Eurasian margin before and after the continued India-Asia collision.

The exposed mid-crustal rocks of the Himalayan orogen provide a natural laboratory for constructing the kinematic evolution of the midcrust during a large-scale continental collision. Kinematic models provide testable, geometrically valid, internally consistent, integrated solutions for diverse geological data from deformed regions. We investigated the Tama Kosi region of east-central Nepal with structural, geochemical, and geochrono logical methods to refine a detailed kinematic model for the Miocene Epoch, during which the mid-crust was pervasively deformed, translated southward, and progressively stacked via basal accretion. Geochemical and U-Pb zircon data demonstrate that two similar orthogneiss bodies were derived from different protoliths, one formed through vapor-absent melting at 1940 ± 16 Ma and the other via vapor-present melting at 1863 ± 14 Ma, respectively, indicating that they do not reflect structural repetition. In situ Th-Pb monazite petrochronology from the Mahabharat Range links the orogenic foreland to the exposed mid-crust of the High Himalaya via a coeval, protracted metamorphic growth-crystallization and/or recrystallization record spanning late Eocene or early Oligocene to early Miocene. Differential cooling of white mica, evidenced by 40 Ar/ 39 Ar cooling ages across the studied area, may outline a previously unrecognized out-of-sequence thrust, the occurrence of which is coincident with the location of a sharp break previously recognized from quartz crystallographic fabric deformation temperatures. Together with previous work, these data form the basis for a new, internally consistent kinematic model for rocks of the Tama Kosi region during the Miocene Epoch that tracks the transition from distributed ductile deformation in the mid-crust to deformation along discrete surfaces during their exhumation.