摘要
系统研究了西藏雅鲁藏布江蛇绿岩带中部日喀则地区德村、吉丁和昂仁蛇绿岩中基性岩石的元素与 Sr-Nd-Pb 同位素地球化学特征。这些基性岩石,包括玄武岩、辉长岩和辉绿岩,属于低钾拉斑玄武岩系列,球粒陨石标准化稀土元素分配模式为轻稀土元素亏损的 N-MORB 型,(La/Yh)_N=0.31～0.65(除样品 DC993为1.17)。在原始地幔标准化微量元素图上,亏损高度不相容元素,与 N-MORB 配分模式一致。相对于 Th,无 Nb、Ta的亏损,显示样品不是产于 SSZ 环境。经构造环境图解判别,样品落入了 N-MORB 区域内;这些元素成分特征表明样品具有洋中脊环境或成熟的弧后盆地环境属性。Sr、Nd 和 Pb同位素组成特征表明特提斯地幔源区以 DM(亏损地幔)为主,同时存在少量 EMⅡ(富集地幔类型Ⅱ)、Sr,Nd 和 Pb 同位素组成特征还表明特提斯地幔域具有印度洋 MORB 型的 Sr-Nd-Pb 同位素组成特征。本文的结果进一步支持 Zhang et al.(2005)的研究结果,现今印度洋不仅在地理位置上占据了曾经是特提斯洋的大部分,而且它的地幔域还继承了曾经特提斯的地幔域的地球化学特征。
In this paper, elemental and Sr-Nd-Pb isotopic compositions for the basaltic rocks from Decun, Jiding and Angren in Xigaze area along the central Yarlung Zangpo suture zone （ YZSZ ） were studied. The rocks are composed of low-K tholeiitic basalt, and gabbro / diabase. Their Chondrite-normalized REE patterns are similar to N-MORB, with depletion in LREE （ （La/Yb） N = 0.31 - 0.65, except for one sample DC993 having （La/Yb）N of 1.17）. Their primitive mantle-normalized multi-element patterns also show the N-MORB signature, depletion in the highly incompatible elements. All rocks do not exhibit Nb-Ta depletion relative to Th, suggesting that they are not associated with supra-subduction processes. The rocks fall in the fields of typical N-MORB in the tectonic setting discrimination diagrams. These features as a whole indicate that the rocks are formed in the mid-ocean-ridge or mature back-arc settings. The Sr-Nd-Pb isotopic compositions of Xigaze ophiolites show that the Tethyan mantle is dominated by depleted mantle （DM） and minor enriched mantle Ⅱ （EMⅡ）. The Sr-Nd-Pb isotopic compositions also indicate that Tethyan mantle has clear Indian MORB- type isotopic signature. Our data intensity the previous study by Zhang et al. （2005） that the Indian sub-oceanic mantle was probably inherited from the Tethyan asthenosphere.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2006年第12期2875-2888,共14页
Acta Petrologica Sinica
基金
国家重点基础研究发展规划项目（编号：2002CB412603）；国家自然科学基金（40473020,40103003,40503005,40572048,40672044）；国土资源部青藏专项计划（200101020401）；高等学校学科创新引智计划（E07011）；中国地调局综合研究项目、中科院广州地化所同位素开放实验室基金和中国国家留学基金资助.
