The significance of Upper Jurassic felsic volcanic rocks within the incipient, intraoceanic Dras Arc, Ladakh, NW Himalaya

Abstract:

The Dras Arc is an island arc terrane located along the Indus Suture within the Ladakh Himalaya. To the north it is juxtaposed against the Eurasian Ladakh Batholith and to the south thrust over the Lamayuru Complex and Indian passive margin. Establishing the timing of inception and final collision of the Dras Arc is imperative to reconstructions of Neotethyan Ocean and timing of arc-continent collisions, prior to the terminal India-Asia continental collision. We describe and date felsic tuffs and adakitic felsic volcanic rock interbedded within the dominantly basaltic-andesitic Dras volcanic complex. These felsic volcanic units yield Upper Jurassic zircon U-Pb ages of 161 ± 1 and 152 ± 1 Ma respectively, making these the oldest reported units within the Dras Arc. We also report zircon U-Pb geochronologic and whole rock geochemical results for the Kargil Intrusive Suite which intrude the volcanic complex. Ages for the intrusives have been reproduced (102 ± 1 Ma and 101 ± 1 Ma), and a second, much younger phase (79 ± 1 Ma) has been identified as one of the youngest igneous phases within the Dras Arc. The presence of felsic, adakitic volcanism early in the evolution of the Dras Arc is consistent with the adolescent stages of island arc systems, in which dehydration melting of underplated arc or subducted oceanic crust generates small volumes of felsic magmas. Thus, the intraoceanic Dras Arc initiated in the Neotethyan Ocean during the Upper Jurassic, much earlier than previously reported, and possibly right up to collision during the late Paleocene between 60-50 Ma. It is likely that the Dras Arc developed together with the Spongtang Ophiolite-Spong Arc complex and the intraoceanic Zedong terrane of Tibet, first before colliding and accreting onto the passive margin of India prior to the terminal India-Asia continental collision.