Geochronologic constraints on the tectonic evolution and exhumation of Nanga Parbat, western Himalaya syntaxis, revisited

We examine the timing of deformation and exhumation of the Nanga Parbat-Har amosh massif in the western syntaxis of the Himalaya. This study presents g eochronologic and thermochronologic data obtained from basement, shear zone , and intrusive units within the massif to reveal the Cenozoic tectonic evo lution of the massif and to document the extent of the Plio-Pleistocene tec tonic activity. These results combined with structural and petrologic obser vations indicate that the western Himalayan syntaxis was tectonically activ e for a protracted length of time and that the deformational succession was punctuated by three episodes since the beginning of the India-Asia collisi on: (1) The western syntaxial Indian plate rocks (future Nanga Parbat) unde rwent metamorphism, melting, and deformation during the initial collision o f India with Asia and the associated island arc, the result of which is rec orded as Eocene to Early Miocene metamorphic and magmatic ages and Oligocen e cooling preserved in the Indian cover metasedimentary sequences that flan k the younger, high-grade core. (2) Transpression along the South Karakorum fault to the north during the Late Miocene resulted in an episode of crust al scale doming and associated tectonometamorphic processes within the Hima laya syntaxis concurrent with the formation of other Late Miocene domes tha t developed in the Karakorum to the north and east. (3) At the core of the massif during the Plio-Pleistocene, the latest evolutionary stage of Nanga Parbat produced granulite-grade metamorphism, anatectic melting, and rapid cooling with deformation manifested as a pop-up structure, overprinting the Late Miocene doming.