摘要
通过对出露于西藏南部岗巴—定日地区花岗岩体的地球化学研究表明,岩石中SiO2,Al2O3,Na2O和FeO,MgO等的含量均高,贫CaO和Fe2O3;w(SiO2)介于71.40%～73.06%,A/CNK在1.17～1.34之间,为铝和硅过饱和类型的强过铝质花岗岩。岩石的稀土元素总量(ΣREE)为56.80×10-6～89.12×10-6,(La/Yb)N=6.30～18.26,(La/Sm)N=2.62～3.40,ΣLREE/ΣHREE=2.41～4.66;稀土元素配分曲线呈右倾型,具有弱的负铕异常。Nb,Ti等高场强元素具有明显的亏损,而Rb,U,La,Nd,Hf,Eu,Y等大离子亲石元素具有明显的正异常。岩石的87Sr/86Sr初始比值较高,87Sr/86Sr为(0.738 71～0.751 12)。综合研究认为,本区花岗岩的成因为陆壳部分熔融作用形成的,属陆壳改造型强过铝质花岗岩。本区花岗岩岩浆源区岩石成分主要为砂屑岩,其次为泥质岩,是上地壳部分熔融作用的结果。岩石的微量元素标准化曲线图、岩石地R1-R2图解、Rb-(Yb+Ta)和Rb-(Nb+Yb)图解均显示本区岩体形成于同碰撞构造环境的花岗岩,具有同碰撞岩浆活动的特征,是喜马拉雅早期印度板块与冈底斯板块的俯冲碰撞导致的地壳增厚,上地壳部分熔融的产物;为形成于同碰撞构造环境的花岗岩。
The geochemistry of granite in Gangba-Dingri region of the southern Tibet was ana- lyzed and discussed in the paper. It was showed that the granites were rich in SiO2, （71. 40% 73.06%）,Al2O3,Na2O,FeO and MgO and poor in CaO and Fe2O3. A/CN K ratios range from 1.17 tol. 34 and saturate with A1 and Si,belonging to typical strongly peraluminous granite. The EREE=70.80 × 10 6- 134.02 × 10-6 , （La/Yb）N = 6.30 - 18.26, （La/Sm）N = 2. 62 -3. 40, ∑LREE/∑HREE=2.41-4.66. REE diagram shows rightward incline and obvious negative Eu abnormity. High field strength elements such as Nb and Ti show distinct negative anomaly while lithophile elements such as Rb, U, La, Nd, Hf, Eu and Y exhibit obvious positive anomaly. The strongly peraluminous granite has relative high（87 Sr/86 Sr） ratio of 0. 738 71 -0. 751 12. So, the granite was resulted from partial melt of continental crust in the area. The magma of the granite was mainly originated from clast rocks with minor mudstone. Preliminary mantle-normalized trace element spider diagram, R1-R2 diagram, Rb- （Yb＋ Ta） and Rb- （Nb ＋ Yb） diagrams indicated that the granite was formed in syn-collision setting. With the features of the syn-collisional magmatic activity,the granite is the product of partially melting crust in such a geologic condition of crustal thickening resulted from the subduction and collision between the Laha massif and India massif during the early Himalayan.
出处
《矿物岩石》
CAS
CSCD
北大核心
2012年第1期67-73,共7页
Mineralogy and Petrology
基金
国家自然科学基金(编号:40272012)
1:25×104聂拉木县幅区域地质调查项目
关键词
强过铝质花岗岩
地球化学
地壳重熔
构造环境
同碰撞
西藏南部
strongly peraluminous granites
geochemistry
crust remelting
tectonic setting
syn- collision- southern Tibet
