Zircon U-Pb ages and geochemistry of the Early Creta-ceous intrusive rocks in the north of Zabuye salt lake area, Tibet, and their geological significance

The genetic model of the widely distributed magmatism in the Mid-Gangdise belt of Tibet during Early Cretaceous is still controversial. The authors conducted field observation, zircon U-Pb dating and geochemical studies of the intrusions from Zabuye salt lake in the Mid-Gangdise belt. Zircon U-Pb age dating suggests that the the intrusion of Zabuye salt lake magma occurred in two periods (142Ma and 100Ma), and both have intermediate to acidic plutons and gabbro dikes. The first phase plutons are I-type metaluminous and high-k calcalkaline series granitic rocks, whereas the second phase plutons belong to metaluminous high-k calcalkaline series dioritic intrusions. Both intermediate to acidic plutons show enrichment of LILE (Rb, Ba, Th and U) and depletion of HFSE (Nb, Ta), with strong magma mixing characters.The data collected from previous researchers show that the first phase granitic plutons and gabbro dike were induced by the roll-back of the subducted Bangong-Nujiang Oceanic slab, while the second phase plutons and dike resulted from the oceanic slab break-off. The results obtained by the authors provide evidence for the southern direction subduction, roll-back and break-off of the Bangong-Nujiang Oceanic slab.