新疆北天山奎屯河蛇绿岩斜长花岗岩锆石SIMSU-Pb年龄及其构造意义  

SIMS zircon U-Pb age of the plagiogranites from Kuitun River ophiolite and its tectonic implications

作　　者：李超[1,2,3] 肖文交[1,3] 韩春明[1,3] 周可法[3] 张志欣[3] 

机构地区：[1]中国科学院地质与地球物理研究所岩石圈演化国家重点实验室,北京100029 [2]中国科学院大学,北京100049 [3]中国科学院新疆生态与地理研究所新疆矿产资源研究中心,新疆乌鲁木齐830011

出　　处：《地质科学》2013年第3期815-826,共12页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家重点基础研究发展计划项目(编号:2007CB411307);国家自然科学基金项目(编号:40725009;41190072;41230207;41202150);国家"305"项目(编号:2011BAB06804;2007BAB25804)资助

摘　　要：作为中亚造山带南部的最终缝合界线,天山一索伦缝合带记录了古亚洲洋晚期的扩张消减历史。本文对新疆北天山混杂带中奎屯河蛇绿岩的斜长花岗岩进行了SIMS锆石年代学研究及地球化学研究。斜长花岗岩富Na_2O,贫K_2O(<1%)和Al_2O_3(<15%),微量元素含量整体低于标准N-MORB,稀土配分曲线平坦,无明显Eu异常,是典型的洋中脊斜长花岗岩,其结晶年龄代表准噶尔洋盆扩张时代。24组离子探针测年数据显示,斜长花岗岩加权平均年龄为343.1±2.7 Ma。结合区域地质研究,本文认为在晚古生代石炭纪,伴随着哈萨克斯坦山弯构造的逐渐形成,准噶尔洋盆持续扩张并向外俯冲于周缘地体之下,形成了东、西准噶尔洋内弧,以及天山和阿尔泰安第斯型陆缘弧。As the last suture of the central Asian orogenic belt, the Tianshan-Solonker suture belt the records the evolution of the Paleoasian ocean in its later period of time. This paper carries out SIMS U-Pb chronological and geochemical study of the plagiogranites from the Kuitun River ophiolite within the north Tianshan m61ange belt. The plagiogranites are enriched in Na20 and depleted in K20 （ 〈 1% ） and A12 03 （ 〈 15 % ）. Their trace element contents are generally lower than the N-MORB, and REE pattern of the plagiogranites is flat with no distinct Eu anomaly. These features demonstrate that the plagiogranites from the Kuitun River ophiolite are typical plagiogranites generated in the mid-ocean ridge,whose ages could stand for the time of oceanic spreading. 24 groups of chronological analysis provide a concordia age of 342.8 ＋ 2.6 Ma. Combined with previous regional geological study, we conclude that the Junggar ocean was continually spreading and subducting outward beneath its surrounding terranes accompanied by gradual formation of the Kazakhstan orocline,producing the eastern and western Junggar intra- oceanic arcs, and Tianshan and Ahai Andes-type continental arcs.

关 键 词：蛇绿岩 斜长花岗岩 锆石U-PB年龄 天山 中亚造山带 

分 类 号：P588[天文地球—岩石学] P597[天文地球—地质学]