Sensitive High Resolution Ion Micro‐Probe U‐Pb Zircon Geochronology and Geochemistry of Mafic Rocks from the Pulan‐Xiangquanhe Ophiolite, Tibet: Constraints on the Evolution of the Neo‐tethys

Abstract

Abstract: The Pulan‐Xiangquanhe ophiolite in the western Yarlung Tsangpo suture zone of Tibet is investigated for its geochemistry, geochronology, and tectonic implications in detail. Sensitive high resolution ion micro‐probe zircon U‐Pb dating reveals that diabases in the ophiolite from the three locations of Xugugab, Mapam Yum Co and La'nga Co are dated at 122.3 ± 2.5 Ma, 118.8 ± 1.8 Ma and 120.5 ± 1.9 Ma, respectively. These early Cretaceous mafic rocks have Na 2 O+K 2 O, rare earth element patterns, trace elemental spider diagram and other geochemical fingerprints of typical mature back‐arc basin affinity. Therefore, the Pulan‐Xiangquanhe ophiolite formed under a mature back‐arc basin environment, which was a product of this intra‐oceanic subduction system. A suprasubduction system could have existed in the southern margin of Eurasia, which involved both intra‐oceanic and continent‐ward subductions. Extension dominated the southern margin of the Eurasian continent during the early Cretaceous.