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  

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

作　　者：刘函[1] 王保弟 陈莉[1] 王立全[1] 张予杰[1] 李俊[1] 苟正彬[1] 张士贞 LIU Han;WANG Baodi;CHEN Li;WANG Liquan;ZHANG Yujie;LI Jun;GOU Zhengbin;ZHANG Shizhen(Chengdu Center,China Geological Survey,Chengdu 610081,Sichuan,China;China Aero Geophysical Survey and Remote Sensing Center for Natural Resources,Beijing 100083,China)

机构地区：[1]中国地质调查局成都地质调查中心,四川成都610081 [2]中国自然资源航空物探遥感中心,北京100083

出　　处：《地质通报》2021年第11期1836-1851,共16页Geological Bulletin of China

基　　金：中国地质调查局项目《中尼铁路沿线(境内段)区域地质调查》(编号:DD20211195);国家自然科学基金项目《西藏那曲地区中晚侏罗世拉贡塘组沉积作用对班公湖-怒江构造带地质演化的制约》(批准号:41972113);《羌塘中部泥盆纪—石炭纪岩浆作用对古特提斯洋构造演化的制约》(批准号:41773026);《措勤—改则地区木纠错组时代厘定:对拉萨地块晚二叠世—三叠纪沉积演化的制约》(批准号:42002032);科技部青藏科考项目《深时特提斯生物与环境演变》(编号:2019QZKK0706)。

摘　　要：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SiO_(2)及极低的K_(2)O、Na_(2)O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。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 SiO_(2)and very low K_(2)O and Na_(2)O 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.

关 键 词：雅鲁藏布江结合带 日喀则 早白垩世 洋内弧 弧前蛇绿岩 初始俯冲 

分 类 号：P534.53[天文地球—古生物学与地层学] P588.12[天文地球—地质学]