U-Pb zircon crystallization age of the Muslim Bagh ophiolite: enigmatic remains of an extensive pre-Himalayan arc

Abstract

The pre-Himalayan evolution of Tethys is fundamental in interpreting the signifi cance of India's Paleogene deceleration and the timing of the India-Eurasia collision-the archetype continental collision that governs our understanding of collisional processes. Here we date zircons from plagiogranite sheeted dikes in the Muslim Bagh ophiolite that yield a U-Pb age of 80.2 ± 1.5 Ma. This age is interpreted as dating the crystallization of plagiogranites that occur at the top of gabbro plutons as well as within sheeted dikes. These represent highly fractionated magma chamber differentiates. The plagiogranite's trace element abundances are typical of subduction petrogenesis and can be explained by the addition of slab-derived components to a depleted mantle wedge. Muslim Bagh ophiolite formation was coeval with the Spongtang Arc in a similar tectonic environment. We interpret the chain of ophiolites within western Pakistan as corollaries of the Spongtang Arc that formed ~15 Ma before they were obducted on the Indian passive margin. These form an extensive arc system that developed as oceanic crust in Tethys foundered during India's migration north. Latest Maastrichtian ophiolite-sole formation and subsequent Paleocene obduction of the arc onto India was the fi rst arc-India collision-a herald of the collisions to come later. © 2012 Geological Society of America.