羌塘地块北部东月湖始新世高Mg^#埃达克质火山岩的成因以及构造意义  

Dongyue Lake adakitic volcanic rocks with high Mg^# in north Qiangtang block： Petrogenesis and its tectonic implication

作　　者：董彦辉[1,2] 王强[1] 许继峰[1] 资锋[1,2] 

机构地区：[1]中国科学院广州地球化学研究所同位素年代学和地球化学重点实验室,广州510640 [2]中国科学院研究生院,北京100039

出　　处：《岩石学报》2008年第2期291-302,共12页Acta Petrologica Sinica

基　　金：中国科学院知识创新工程重要方向性项目(KZCX3-SW-143);国家973项目(2002CB412602);国家杰出青年基金项目(40425003)资助

摘　　要：东月湖火山岩分布于多格错仁-祖尔肯乌拉山一带，这里发育有青藏高原最早的后碰撞岩浆活动。东月湖火山岩的锆石SHRIMP U-Pb测年得到了44．3±1．8Ma的年龄。岩石地球化学的结果表明东月湖火山岩是一套高钾钙碱性的中酸性岩，具有埃达克岩的地球化学特征，如富集LILEs，亏损HFSEs，具有高的Sr含量和Sr／Y比值和强的LREE／HREE分异，表现出弱的正Eu异常。同时，这些岩石也具有相对高的Mg^#和相容元素含量。这些特点与中国东部高Mg^#的埃达克质岩类似，很可能是下地壳拆沉的产物。东月湖火山岩指示了在44Ma左右青藏高原北部可能发生过一期加厚下地壳的拆沉事件。The lavas near by the Dongyue Lake area is a part of Cenozoic Duoge Coring-Zhuerken Wula Mountain volcanic province, which is the earliest post-collision magmatic activity recognized in the Tibetan plateau. SHRIMP U-Pb zircon dating obtains an age of 44. 3 ± 1.8Ma for a Dongyue Lake lava. In geochemistry, the Dongyue Lake lavas are intermediate-acid rocks, their SiO2 range of 55% 67% , belonging to high-K calc-alkaline series. In addition, they show enrichment of LILEs and LREE, depletion of Y and HREE, as well as have gentle positive Eu anomaly,high Sr concentration and Sr/Y ratios. So they display geochemical characteristics similar to those of an adakite rock defined by Defant and Drumond（1990）. Meanwhile, the Dongyue Lake lavas also have high Mg^# （ Mg / Mg ＋ F101al） and high compatible elements such as Cr and Ni contents. We suggest that the Dongyue Lake adakitic lavas were generated by partial melting of a delaminated lower crust, similar to the petrogenesis of the high Mg^# adakitic rocks in east China. Thus, eruption of the Dongyue Lake adakitic rocks probably indicates that an Eocene delamination event took place beneath north Qiangtang block.

关 键 词：羌塘 青藏高原 多格错仁 埃达克质岩 拆沉作用 

分 类 号：P588.144[天文地球—岩石学]