西藏羌塘中部玛依岗日地区印支期花岗岩的地球化学特征及其形成环境  

Geochemistry and tectonic settings of Indosinian granites in the Mayêr Kangri area,central Qiangtang,Tibet,China.

作　　者：黄小鹏[1] 李才[1] 翟庆国[2] 

机构地区：[1]吉林大学地球科学学院 [2]中国地质科学院地质研究所,北京100037

出　　处：《地质通报》2007年第12期1646-1653,共8页Geological Bulletin of China

基　　金：国家自然科学基金项目(编号:40672147);中国地质调查局项目(编号:200113000065)联合资助

摘　　要：羌塘中部玛依岗日地区出露有一处印支期强过铝质钙碱性花岗岩(SP),属于S型花岗岩(CPGs的一种),不同于西藏南部广大的过铝质花岗岩(MPGs)。该花岗岩的地球化学特征表现为:A/CNK>1,刚玉标准分子的质量分数均大于1.21%,低Sr、Ba、Ti,富K、Rb、Th,稀土元素球粒陨石标准化曲线具有略微右倾的V字形特征,具较强烈的Eu负异常(δEu=0.26～0.53,平均0.36)。CaO/Na2O<0.3,表明源岩为泥质岩石;Al2O3/TiO2<100,表明其为高温型(≥875℃)花岗岩。另外,该花岗岩(SP)与蓝片岩、榴辉岩的形成时代相同。在印支期晚期冈瓦纳大陆与欧亚大陆碰撞的过程中,炽热的幔源岩浆的底侵或注入引起了地壳中泥质源岩的脱水熔融,最终形成了该区的过铝质钙碱性花岗岩。Indosinian strongly peraluminous calc-alkaline granites （SP） are exposed in the Mayer Kangri area, central Qiangtang, Tibet. They belong to S-type granites （CPGs）, also called cordierite-bearing, biotite-rich peraluminous granites, which are different from muscovite-beating peraluminous granites （MPGs） exposed extensively in southern Tibet. The geochemical characteristics of the gran- ites are as follows： A/CNK〉1; the corundum standard molecular mass fractions are all higher than 1.21%; K, Rb and Th are enriched and St, Ba and Ti are depleted; the chondrite-normalized REE distribution patterns show the slightly right-inclined ＂V＂-shaped feature, with a relatively strong negative anomaly （δEu=0.26-0.53, averaging 0.36）. The CaO/Na2O ratios of the granites are 〈0.3, suggesting that the granites were derived from pelitic sources. The Al2O3/TiO2 ratios are 〈100, suggesting that the granites formed at high temperatures （≥875℃）, In addition, the age of the SP granites is the same as that ofblueschist and eclogite. During the late Indosinian collision between Gondwanaland and Eurasia, the underplating or injection of hot mande-derived magmas led to dehydration-melting ofpelitic source rocks, and finally the strongly peraluminous high-K calc-alkaline granites were formed.

关 键 词：西藏羌塘地区 强过铝质花岗岩 印支期 同碰撞 

分 类 号：P588.121[天文地球—岩石学] P595[天文地球—地质学]