中拉萨地块亚热地区早白垩世辉长岩:班公湖-怒江洋南向俯冲板片断离的岩浆作用响应  

The Early Cretaceous gabbro in Yare area,middle Lhasa Block:Magmatism response to the slab break-off of the southward subduction Bangong-Nujiang Ocean lithosphere

作　　者：张士贞 李奋其[1] 刘函[1] 李俊[1] 苟正彬[1] 秦雅东[1] ZHANG Shizhen;LI Fenqi;LIU Han;LI Jun;GOU Zhengbin;QIN Yadong(Chengdu Center,China Geological Survey,Chengdu 610081,Sichuan,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

出　　处：《地质通报》2021年第11期1852-1864,共13页Geological Bulletin of China

基　　金：中国地质调查局项目《中尼铁路(境内段)沿线区域地质调查》(编号:DD20211195);《三江造山带昌都—澜沧地区区域地质调查》(编号:DD20190053);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);《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)。

摘　　要：为深入认识拉萨地块中北部地区早白垩世构造-岩浆过程,对中拉萨地块西段亚热地区早白垩世辉长岩进行了研究。辉长岩的锆石U-Pb年龄为115.5±0.5 Ma。岩石属于拉斑玄武岩系列,具有与洋岛玄武岩(OIB)相似的稀土元素特征,Mg#值(46.07~48.05)、Cr(6.97×10^(-6)~18.5×10^(-6))和Ni(6.87×10^(-6)~11.2×10^(-6))元素含量较低,Rb、Ba、K、Sr等大离子亲石元素富集,Th、U和Pb元素呈现明显的正异常,Nb、Ta、Zr、Hf、P、Ti等高场强元素表现为负异常,显示具有部分弧火山岩性质;具有正的锆石εHf(t)值(+4.3~+7.9)和较年轻的Hf亏损地幔模式年龄(T DM1=489~614 Ma)。综合分析认为,亚热地区早白垩世辉长岩形成于南向俯冲的班公湖-怒江特提斯洋岩石圈板片断离的构造背景,可能是受近期俯冲板片熔体或超临界流体交代的软流圈地幔部分熔融的产物,并经历了不同程度的分离结晶作用。In order to understand the Early Cretaceous tectonic-magmatic process in the central and north Lhasa Block,the Early Cretaceous gabbro in the Yare area of western part of middle Lhasa Block were studied.The zircon U-Pb age of gabbro is 115.5±0.5 Ma.The rocks belong to tholeiite series,and their characteristics of rare earth elements are similar to those of oceanic island basalt(OIB).Mg#value(46.07~48.05)and contents of Cr(6.97×10^(-6)~18.5×10^(-6)),Ni(6.87×10^(-6)~11.2×10^(-6))are relatively low.The large ion lithophile elements such as Rb,Ba,K,Sr of gabbro samples are relatively enriched,Th、U and Pb show positive anomalies,and the high field strength elements such as Nb,Ta,Zr,Hf,P and Ti show negative anomalies,indicating that the gabbro samples have some“arc volcanic rock”properties.The gabbro show positive zirconεHf(t)values(+4.3~+7.9)and younger Hf-depleted mantle model ages(T DM1)of 489~614 Ma.By comprehensive analysis,it is proposed that the Early Cretaceous gabbro in the Yare area is most likely triggered by the slab break-off of the southward subducting Bangong-Nujiang Tethyan Ocean lithosphere,and can be considered as the product of partial melting of the asthenosphere mantle which was metasomatized by recent melts or supercritical fluids from the subduction slab,and subsequently experienced varying degrees of fractional crystallization.

关 键 词：中拉萨地块 亚热地区 早白垩世 辉长岩 板片断离 

分 类 号：P534.53[天文地球—古生物学与地层学] P588.124[天文地球—地质学]