西藏雅鲁藏布江缝合带东段泽当地幔橄榄岩特征及其意义  

The characteristics and significance of Zedang peridotite in eastern Yarlung-Zangbo suture in Tibet

作　　者：来盛民 杨经绥[1,2] 熊发挥[2] 刘钊[1] 田亚洲[2] 徐向珍[2] 张岚[1] 高健[3] 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]大陆构造与动力学国家重点实验室、中国地质科学院地质研究所,北京100037 [3]昆明理工大学,昆明650504

出　　处：《岩石学报》2015年第12期3629-3649,共21页Acta Petrologica Sinica

基　　金：国家行业专项(SinoP robe-05-02);国家自然科学基金重点项目(40930313);国家自然科学基金创新群体项目(40921001);国家自然科学基金项目(41502062);地质调查项目(1212011121263);中国地质科学院地质研究所基本科研业务费项目(J1526)联合资助

摘　　要：泽当岩体位于雅鲁藏布江缝合带东段,主要由地幔橄榄岩、辉长辉绿岩和基性火山岩等组成。地幔橄榄岩主要为方辉橄榄岩和二辉橄榄岩,有少量透镜状纯橄岩。地幔橄榄岩经历了强烈的塑性变形作用。地幔橄榄岩中橄榄石的Fo值为89.6~91.8,属镁橄榄石;斜方辉石为顽火辉石,En 87.8~90.3;单斜辉石En 44.1~50.0,主要为顽透辉石和透辉石。铬尖晶石的Cr#值（=100×Cr/（Cr＋Al））为17.0~93.6,其中,二辉橄榄岩和方辉橄榄岩中的铬尖晶石为富铝型尖晶石,纯橄岩中的铬尖晶石Cr#最高,为富铬型尖晶石。地幔橄榄岩的部分熔融程度为17%~34%,表明泽当地幔橄榄岩可能经历了多阶段的过程。亏损的主量元素组成和低于原始地幔的稀土元素含量（0.15×10-6~0.61×10-6）指示泽当地幔橄榄岩为经历过部分熔融和熔体抽取的亏损残余地幔岩石。REE配分型式为中稀土亏损的＂V＂型或＂U＂型,原始地幔标准化元素比值（La/Sm）N为0.5~8.0,表明泽当地幔橄榄岩经历过交代作用。矿物化学与地球化学数据表明泽当地幔橄榄岩形成于MOR环境,后受到SSZ环境的改造。The Zedang mafic-ultramafic body crops out in the eastern Yarlung-Zangbo suture zone of Tibet. This massif consists of mantle peridotite,gabbro,diabase and volcanic rocks. The mantle peridotites are mostly harzburgite,lherzolite and a few harzburgite with chromite. A dike-like bodies of dunite are also present. Mineral structures show that the peridotites experienced plastic deformation and partial melting. The Fo values of olivine vary in the range of 89. 6 ~ 91. 8 and all olivines are forsterite. The orthopyroxenes are enstatite,the En values vary from 87. 8 to 90. 3. Clinopyroxenes are mainly endiopside and diopside and the En values of clinopyroxene vary in the range of 44. 1 ~ 50. 0. The spinels have Cr#values from 17. 0 to 93. 6. The aluminum-rich spinels are from harzburgite,lherzolite and the chromium-rich are from dunite. The degree of partial melting of mantle peridotite is 17% ~34%,indicating that Zedang mantle peridotite may experience a multi-stage process. The depleted major element compositions and low REE content（ 0. 15 × 10- 6~ 0. 61 × 10- 6）,which is lower than that of the primary mantle,indicating that the Zedang ultramafic rocks belonged to depleted residual mantle rocks after a significant degree of partial melting and melt extraction. Their primary mantlenormalized REE patterns are all U- or V-shaped with（ La / Sm）Nbeing 0. 5 ~ 8. 0（ primary mantle-normalized values）. These features are consistent with the opinion that the Zedang ultramafic rocks were formed by the interaction of depleted residual mantle rocks with melts / fluids. The mineralogy and geochemistry of the Zedang peridotites suggest that they formed originally at a mid-ocean ridge（ MOR） and were later modified by suprasubduction zone（ SSZ） melts.

关 键 词：构造背景 地幔橄榄岩 部分熔融 泽当岩体 雅鲁藏布江缝合带 

分 类 号：P588.125[天文地球—岩石学]