内蒙古额济纳旗拐子湖地区花岗岩地球化学特征及其地质意义

Geochmeical features and geological significance of Granitoid Rocks in Guaizihu,Ejinaqi,Inner Mongolia

内蒙拐子湖一带发现一批中小型Au、Cu矿床（点）,空间上与小型花岗岩株（枝）相伴而生。本文利用岩石地球化学方法结合野外宏观岩石学研究,揭示岩浆源区性质与成矿的内在联系。研究表明,拐子湖花岗岩属高钾过铝质的钙碱性系列,轻、重稀土元素分馏明显,LREE相对富集（（La/Yb）N=3.78~20.13）。微量元素ORG标准化显示,富集Rb、Ba、Th、K等大离子亲石元素（LILE）,亏损Nb、Ta、Sr、P等高场强元素（HFSE）。Sr（（35.82~364.45）×10-6,Yb（0.79~2.51）×10-6属于低Sr、低Yb型花岗岩,岩浆源区为下地壳火山岩（玄武岩）,岩浆形成于碰撞造山-地壳增厚过程诱发的下地壳局部熔融。一系列证据表明,恩格尔乌苏蛇绿岩带所代表的中亚造山带东部古亚洲洋的消失闭合发生在早二叠世末。

A number of small and medium Au and Cu deposits （occurmeces） were found in Guaizihu area, Inner Mongolia, and these deposits were accompanied by small granite strains （branch） in spatial terns. This paper, using petrogeochemistry method and combining the study of macropetrology in the field, revealed the internal relationship of magma source area qualities and mineralization. The results showed that Guaizihu granite belongs to high-K calc-alkaline se- ries with peraluminous characteristics, relatively strong fractionation between light rare earth el- ement （LREE） and heavy rare earth element （HREE）, and relatively enriched in LREE （ （La/ Yb） N=3.78- 20.13）. ORG normalization of trace elements showed that the granites are en- riched in large-ion lithophile elements （LILE） such as Rb, Ba, Th, K and depleted high field strength elements（HFSE） such as Nb, Ta, Sr,P. Guaizihu granite belongs to low Sr and low Yb type. The magmatic source is from lower crust volcanic rock. The magma formed in lower crust partial melting which is induced by the process of collision orogenic - crustal thickening. A se- ries of evidence showed that the disappearing of ancient Asia ocean in the east of Central Asian orogenic belt, which is represented by Engel Usu ophiolite belt, occured at the end of the early Permian.