Xenolith Zircons Record the Long Geological History of India-Asia Convergence: Results From U-Pb Depth Profiling

Abstract

Continental crust forms in magmatic arcs and transforms through collision, as seen in the Tibetan crust shaped by Neo-Tethyan subduction and India-Asia collision. We examine zircons from crustal granulite xenoliths using U-Pb depth profiling to reveal a 220-million-year evolutionary history in southern Tibet. Our data provide age history consistent with the Gangdese magmatic rocks. From 100 Ma, our results show numerous age peaks linked to the arrival of the Indian continent, associated with fast convergence, slab rollback, and eventual slab breakoff. During the post-collisional stage, the growth of zircon rims indicates a resurgence of metamorphism and anatexis, and contemporaneous shifts in Th/U ratios and (Dy/Yb)_N values reflect an increase in crustal thickness. We suggest the capacity of zircon overgrowth to capture geological episodes during crustal evolution. In this case, granulite xenoliths from single areas through zircon depth profiling can offer substantial insights into the geological processes shaping the collisional orogen.