江南造山带西段桂北四堡地区830 Ma辉长岩锆石SIMS U-Pb年代学和岩石地球化学特征及其岩石成因研究  

Geochronology and geochemistry of 830Ma gabbro in the western segment of the Jiangnan Orogen and constraint on its petrogenesis

作　　者：寇彩化[1] 刘燕学[1] 李江 李廷栋[1] 丁孝忠[1] 刘勇[1] 靳胜凯 KOU Caihua;LIU Yanxue;LI Jiang;LI Tingdong;DING Xiaozhong;LIU Yong;JIN Shengkai(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Guangxi Zhuang Autonomous Region Geological Survey Institute,Nanning 530023,China;China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]广西壮族自治区地质调查院,广西南宁530023 [3]中国地质大学(北京),北京100083

出　　处：《地学前缘》2022年第2期218-233,共16页Earth Science Frontiers

基　　金：中国地质调查局项目(1212011120117,1212011120115);国家自然科学基金项目(41972069)。

摘　　要：本次研究对象为江南造山带西段桂北四堡地区新元古代辉长岩,主要由斜长石和单斜辉石组成,含有少量的橄榄石和钛铁氧化物,表明在岩浆演化过程中发生了斜长石和单斜辉石以及少量橄榄石的分离结晶作用。辉长岩锆石SIMS U-Pb谐和年龄为(830±7)Ma,指示其侵位年龄约为830 Ma。全岩具有低SiO_(2)含量(48.46%~53.99%)、高MgO含量(9.27%~25.22%)、Mg^(#)值较高(62~79)的特征。辉长岩为钙碱性系列岩石,其稀土元素球粒陨石标准化和微量元素原始地幔标准化与典型的弧岩浆相似,具有相对富集轻稀土元素((La/Yb)_(N)=2.2~3.7,(La/Sm)_(N)=2.5~2.9)和大离子亲石元素,明显的高场强元素(Nb、Ta和Ti)亏损的特征,还具有较高的Th/Nb比值(0.7~0.8)和低Nb/La比值(0.4~0.6)。辉长岩具有负的ε_(Nd)(t)值(-6.3~-3.0)和正的ε_(Hf)(t)值(8.0~12.1),指示其源区为亏损地幔,但有富集组分加入。结合区域地质特征,推测辉长岩形成于活动大陆边缘俯冲构造背景,起源于受沉积物流体交代了的楔地幔。We report gabbro discovered in the western segment of the Jiangnan Orogen Belt,Sibao area,northern Guangxi Province.The gabbro contains mostly plagioclase and clinopyroxene and a small amount of olivine and Fe-Ti oxide minerals,indicating likely fractionation of plagioclase,clinopyroxene and some olivine within the magma chamber.The gabbro specimen has a zircon SIMS U-Pb age of(830±7)Ma,suggesting gabbro emplacement at~830 Ma.The bulk-rock is characterized by relatively low SiO_(2)(48.46%-53.99%)and high MgO(9.27%-25.22%)contents with Mg^(#)of 62-79.It belongs to typical calc-alkalic arc rock,characterized by enrichments of light rare earth elements and large-ion lithophile elements relative to heavy rare earth elements((La/Yb)_(N)=2.2-3.7,(La/Sm)_(N)=2.5-2.9),significantly negative Nb,Ta and Ti anomalies,and relatively high Th/Nb(0.7-0.8)and low Nb/La(0.4-0.6)ratios.The gabbro specimen has negativeε_(Nd)(t)(-6.3-3.0)and positiveε_(Hf)(t)(8.0-12.1),indicating it is sourced from depleted mantle with the addition of enriched components.In combination with the regional geology,we infer the gabbro is derived from depleted mantle wedge metasomatized by sediment-derived fluids and formed in the active continental margin in a subduction setting.

关 键 词：江南造山带西段 新元古代基性岩 锆石SIMS U-Pb年龄 岩石成因 构造背景 

分 类 号：P597[天文地球—地球化学] P581[天文地球—地质学]