西藏扎布耶茶卡北部早白垩世侵入岩锆石U-Pb年龄、地球化学特征及其地质意义

中冈底斯带在早白垩世发生的大规模岩浆爆发事件的成因模式仍然存在争议。对中冈底斯带扎布耶茶卡北部区域岩浆岩的野外特征、锆石U-Pb年龄、全岩地球化学特征进行研究,结果表明,扎布耶茶卡北部岩体主要侵位于142Ma和100Ma,2期岩浆作用均包含中酸性岩体和辉长岩脉体。第一期(约142Ma)岩体属I型偏铝质高钾钙碱性系列花岗质岩体,第二期(约100Ma)岩体为偏铝质高钾钙碱性系列闪长质岩体。2期中酸性岩体均富集Rb、Ba、Th、U等大离子亲石元素,相对亏损Nb、Ta等高场强元素,并显示强烈的壳-幔岩浆混合特征。结合前人研究资料,扎布耶茶卡北部第一期花岗质岩体及辉长岩脉为南向俯冲的班公湖-怒江洋壳板片回转引起的岩浆作用;第二期闪长质岩体及辉长岩脉为班公湖-怒江洋壳板片断离的岩浆作用的响应。该研究成果为班公湖-怒江洋的南向俯冲、板片回转和板片断离演化模式提供了岩浆作用证据。

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 calc-alkaline 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 di-rection subduction, roll-back and break-off of the Bangong-Nujiang Oceanic slab.