Discovery of the boninite series volcanic rocks in the Bangong Lake ophiolite mélange,western Tibet,and its tectonic imp
The boninite series volcanic rocks, mainly composed of basaltic andesite, andesitic lava breccia and andesite porphyrite, were recognized for the first time in the Bangong Lake ophiolite mé1ange, western Tibet. These rocks have a strong boninitic affinity, with high SiO2 (55.61％-59.23％,weight percent), MgO (6.63％-13.08％, 9.13％ on average (weight percent)), A1203/1iO2 ratios (36-54), Mg# (0.61-0.74), Ni (116 ppm on average) and Cr (354 ppm on average)low TiO2 (0.23％-0.39％, weight percent), and strong LILEs enrichment relative to the depleted HFSEs. C1-chondrite normalized (La/Gd)N and (Gd/Yb)N ratios of about 1.70 and 0.83, respectively, produce prominent“U-shaped” normalized REE (rare earth element) patterns. Such a close compositional affinity to boninite indicates that these volcanic rocks were formed in a forearc setting produced by the intra-oceanic subduction.
作 者： SHI Rendeng YANG Jingsui XU Zhiqin QI XueXiang 作者单位： Laboratory of Continental Dynamics of Ministry of Land and Resources of China, Institute of Geology, Chinese Academy of Geological Sciences,Beijing 100037, China 刊 名： 科学通报(英文版) SCI 英文刊名： CHINESE SCIENCE BULLETIN 年，卷(期)： 2004 49(12) 分类号： P5 关键词： ophiolite mé1ange boninite intra-oceanic subduction Bangong Lake Tibet