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UBC Theses and Dissertations

Tectonometamorphic evolution of the Hindu Kush, North West Pakistan Fasial, Shah


New U-(Th)/Pb geochronology, geochemical analyses of plutonic bodies and thermochronologic constraints from the Hindu Kush range, NW Pakistan, provide insight on the crustal growth and tectonic evolution of the southern Eurasian margin and Himalaya-Karakoram-Tibet orogen. Monazite and zircon data record a protracted deformational, metamorphic, and magmatic history that spans the Cambrian to the Neogene. The Cambrian-Ordovician Kafiristan pluton yields geochemical signatures consistent with extensional plutonism and rifting of the Hindu Kush and Karakoram terranes, which now comprise the field area, away from Gondwana. The Hindu Kush accreted to the southern Eurasian margin during the Late Triassic followed closely by the Karakoram terrane in the Early Jurassic. An Andean-style subduction margin was established at the southern Eurasian boundary in the Cretaceous, which lead to the intrusion of the Tirich Mir and Buni-Zom plutons. The attendant volcanic arc magmatism ended with the docking of the Kohistan island arc and the emplacement of the Kohistan-Ladakh batholith during the Late Cretaceous. Eocene ⁴⁰Ar/³⁹Ar muscovite ages in close proximity to the Tirich Mir fault indicate reactivation of the structure during the onset of continent-continent collision. This collision evolved into widespread crustal thickening, high-temperature metamorphism, and associated anatexis in the late Oligocene and early Miocene culminating locally with the emplacement of the Garam Chasma pluton. Thermochronologic data from near the pluton indicate immediate cooling after crystallization, followed by uplift and exhumation during the Neogene. Moreover, a young (1.4 ± 0.5 Ma) apatite fission track date from the Tirich Mir pluton is consistent with active exhumation and uplift of the 7700+ m Tirich Mir peak. This study and the data presented herein provide important new constraints on the nature and timing of tectonic events along the developing south Eurasian margin before and after the continued India-Asia collision.

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