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.
出处
《地质通报》
CAS
CSCD
北大核心
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
关键词
西藏羌塘地区
强过铝质花岗岩
印支期
同碰撞
Qiangtang area, Tibet
strongly peraluminous granites
Indosinian
syn-coUision
