Deposition, burial and cooling of the Indus Basin, Ladakh, Northwest India: implications for orogenic processes in the India-Asia collision zone

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The >2000 km India-Asia collision zone is an archive of Cenozoic tectono-sedimentary processes in the interior of the Himalayan orogenic system. The Indus Basin is a critical element of the India-Asia collision zone in Ladakh, NW India, and contains marine and continental sedimentary sequences, collectively known as the Indus Basin sedimentary rocks. The source of the Indus Basin sedimentary rocks is debated, and burial, uplift and erosional processes in the basin are not well understood. In addition, it is unknown how the Indus Basin attained its present-day elevations of >4-5 km. The goals of this research are to: 1) identify the earliest evidence of Indian plate detrital input in the Indus Basin and ascertain the timing of India-Asia collision, and 2) determine the geodynamic, tectonic, and surface processes involved in burial, uplift and erosion of the Indus Basin as the collision zone evolved. In this dissertation, I investigate the depositional, burial and cooling history of the Indus Basin sedimentary rocks using U-Pb detrital zircon geochronology, (U-Th)/He detrital zircon and apatite thermochronology, and detrital zircon fission-track thermochronology. My U-Pb detrital zircon ages from the oldest continental facies of the Indus Basin record the first arrival of Greater Indian detritus on the Asian plate at ca. 50 Ma, providing a minimum India-Asia collision age. Zircon fission-track ages and thermal modeling of (U-Th)/He zircon and apatite cooling ages in central Ladakh show that the Indus Basin cooled in Miocene-Pliocene time between ca. 18-3 Ma from burial temperatures exceeding 200 °C. I hypothesize that the Miocene cooling was triggered by northward underthrusting of the Indian plate following Greater India slab-break off and was aided by Indus River erosion. Additional (U-Th)/He detrital zircon and apatite cooling ages from western, central and eastern Ladakh confirm that the Miocene-Pliocene cooling signal is regionally present along the Indus Basin, with rapid cooling occurring between ca. 19-14 Ma. The Miocene cooling is in fact a continental-scale thermal event along the India-Asia collision zone that occurred in response to concurrent erosion by the Indus and Yarlung Rivers through an uplifted region produced by northward underthrusting of the Indian plate.

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