科研之友
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摘要
Deciphering the petrogenesis of andesitic/dioritic rocks is fundamental to understanding the formation of the continental crust. Here we present detailed petrology, geochronology, major and trace element, Sr-Nd-Hf-O isotope data for the Early Cretaceous (approximate to 122 Ma) dioritic rocks in the Bizha area in southern Qiangtang, Tibet. The dioritic rocks are characterized by large ion lithophile elements, Pb, and light rare earth elements but depletion of high field strength elements with slightly enriched and variable epsilon Nd(t) values of -0.01 to -3.31 and initial Sr-87/Sr-86 isotopic ratios of 0.7053-0.7062. They also have variable magmatic zircon Hf-O isotope compositions (epsilon Hf(t)=-5.3 to +3.6 and O-18=+7.3 to +9.5 ). Combined with contemporary andesitic lavas in southern Qiangtang, we suggest that the intermediate magmatic rocks in this area were most probably derived by partial melting of a subduction melange, which is a mixture of mid-oceanic ridge basalts (MORBs), sediments, and mantle wedge peridotites, formed along the interface between the subducted slab and the overlying mantle wedge in a subduction channel before approximate to 124 Ma. The melange diapir melting was triggered by the asthenospheric upwelling and hot corner flow caused by roll-back of the northward subducted Bangong-Nujiang oceanic slab during the Early Cretaceous. The Early Cretaceous intermediate magmatic rocks in southern Qiangtang have an overall continental crust-like andesitic composition. Therefore, partial melting of melange provides an important support for the generation of andesitic magmas in continental arcs and the andesite model for crustal growth.
- 出版日期2016-5
- 单位中国科学院地质与地球物理研究所兰州油气资源研究中心; 中国科学院大学; 中国科学院地质与地球物理研究所; 同位素地球化学国家重点实验室; 中国科学院广州地球化学研究所; 桂林理工大学
