日喀则夏鲁N-MORB型辉长岩与辉绿岩：雅鲁藏布江特提斯洋早白垩世初始俯冲记录

雅鲁藏布江结合带130~120 Ma蛇绿岩分布广泛，但其形成环境存在较大争论。以日喀则地区夏鲁辉长岩及辉绿岩锆石U-Pb定年、主量及微量元素数据为基础，结合大量的日喀则蛇绿岩研究数据，分析蛇绿岩的构造环境及其动力学意义。夏鲁辉长岩LA-ICP-MS锆石U-Pb年龄为123.8±1.1 Ma(MSWD=0.97)，表明其是日喀则130~120 Ma蛇绿岩残片之一。主量、微量元素特征显示，部分辉长岩样品高CaO、低SiO2及极低的K2O、Na2O含量，为异剥钙榴岩化所致，而辉绿岩无流体影响。夏鲁辉长岩与辉绿岩显示正常型大洋中脊玄武岩(N-MORB)特征，且轻稀土元素较N-MORB亏损，来自亏损地幔尖晶石二辉橄榄岩源区高程度部分熔融。日喀则130~120 Ma的蛇绿岩N-MORB型基性岩来自俯冲组分混入不均的地幔源区，表现为洋中脊玄武岩至火山弧玄武岩过渡特征，并且无陆壳物质混入，最有可能形成于洋内弧系统。综合区域地质资料，认为日喀则130~120 Ma的蛇绿岩在发育时限、岩石组合及地球化学特征上与伊豆小笠原-玻安岛-马里亚纳(IBM)弧前蛇绿岩类似，代表雅鲁藏布江新特提斯洋一次洋内俯冲的开始。

Xialu N-MORB gabbros and diabases in the Xigaze ophiolite: Record of subduction initiation of the Yarlung Zangbo Tethyan Ocean at Early Cretaceous

The 130~120 Ma ophiolite is the most widely distributed in the Yarlung Zangbo suture zone, however, its formation environment remains controversial.Based on zircon U-Pb ages, whole-rock geochemical date of Xialu gabbros and diabases, and a large number of data of Xigaze ophiolite, the tectonic environment and dynamic significance of Early Cretaceous ophiolite were discussed.LA-ICP-MS zircon U-Pb dating of the Xialu gabbro yields weighted mean age of 123.8 ± 1.1 Ma(MSWD = 0.97), indicating one of the 130~120 Ma Xigaze ophiolite relics.Some gabbro samples are characterized by high Cao, low SiO2 and very low K2O and Na2O contents, which can be attributed to a rodingitization process, whereas diabases suffer from minimal affection of fluid.Xialu gabbros and diabases show N-MORB type characteristics and more depleted in light rare earth elements than normal N-MORB, suggesting high degree partial melting of a depleted mantle of spinel lherzolite source.The N-MORB basic rocks of the 130~120 Ma ophiolite in Xigaze were generated from a mantle source with inhomogeneous mixture of subduction components, and characterized by the transition from MORB to VAB, with a minimal adding of continental crust, which suggest that the Xigaze ophiolite was formed in an intra-oceanic arc system.Combined with regional geology, it is suggested that the 130~120 Ma ophiolite in Xigaze is similar to the IBM fore-arc ophiolite in development time, lithology and geochemistry, representing a subduction initiation in the Yarlung Zangbo Tethys Ocean.