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

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 Na2O+K2O, 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.