冈底斯带巴嘎区二云母花岗岩SHRIMP锆石U-Pb定年  

SHRIMP U-Pb Dating of Zircons from Two-Mica Granite in Baga Area in Gangdise Belt

作　　者：和钟铧[1] 杨德明[1] 王天武[1] 郑常青[1] 

机构地区：[1]吉林大学地球科学学院,吉林长春130061

出　　处：《吉林大学学报（地球科学版）》2005年第3期302-307,共6页Journal of Jilin University：Earth Science Edition

基　　金：国土资源部地质调查项目(H46002002)

摘　　要：二云母花岗岩出露于冈底斯弧背断隆带上,沿色日荣-巴嘎东西向断层呈串珠状分布.岩石具有高SiO2、K2O、Al2O3,低CaO的特点,A/CNK>1.1,并且标准矿物计算的刚玉质量分数均大于2.1%,为过铝质花岗岩,具深熔花岗岩特点,稀土和微量元素显示该岩石形成于同碰撞构造环境.SHRIMP锆石U-Pb定年结果表明,花岗岩继承锆石给出了少量太古宙和大量1 120～1 489 Ma的年龄,代表了锆石主要源区的物质年龄,这与冈底斯带上念青唐古拉群原岩年龄基本一致,反映二者的亲缘性.有深熔特征的二云母花岗岩深熔时间为139 Ma.结合区域资料,巴嘎区二云母花岗岩是在晚侏罗世时期由于新特提斯洋的俯冲作用及其弧后洋盆的闭合碰撞使冈底斯带地壳增厚熔融的结果.Two-mica granites are exposed in the Gangdise back-arc fault uplift area and are discontinually distributed along Serirong-Baga fault as an E-W trending tring. Their contents of SiO 2, K 2O, Al 2O 3 are higher, but the contents of CaO are lower, A/CNK>1.1 and the content of corundum exceeds 2.1% by CIPW standard mineral calculation. All those show these granites are the peraluminous granites with the rheomorphic remelting characteristics, which formed during the syn-collision circumstances.The results of SHRIMP zircon UPb dating reveal that the inherited zircon in two-mica granitic rocks gave a few Archean and a large number of ages between 1 120 Ma and 1 489 Ma, which represent the age of the main source region of the zircon. Those ages are essentially in agreement with the protolith age of the metamorphic Nianqingtanggu Group, which indicate their close affinity. The rheomorphic remelting age of the two-mica granites is 139 Ma. Combined with the regional data, it is suggested that the two-mica granites were produced due to the crustal thickening which was caused by the Neotethys subducting underneath the Gangdise microblock and by its back-arc oceanic basin closing in the same time.

关 键 词：SHRIMP U—Pb定年 二云母花岗岩 新特提斯洋 冈底斯带 巴嘎区 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]