西天山温泉地区早古生代斜长角闪岩的锆石SHRIMP U-Pb年龄及其地质意义  

SHRIMP U-Pb ages for zircons of the amphibolites and tectonic evolution significance from the Wenquan domain in the West Tianshan Mountains,Xinjiang,China.

作　　者：胡霭琴[1] 韦刚健[1] 张积斌 邓文峰[1] 陈林丽[1] 

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]新疆有色地质勘察局,乌鲁木齐830000

出　　处：《岩石学报》2008年第12期2731-2740,共10页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目"中亚造山与成矿研究"(2001CB409805);国家自然科学基金项目(40803009)资助

摘　　要：西天山温泉县城以南地区出露了以温泉群为基底的前寒武纪变质岩系。其中,被当作温泉群变质岩系一部分的灰色中-粗粒斜长角闪岩,在岩石外观特征上与前寒武纪的深灰色细粒斜长角闪岩截然不同。进一步的地质研究,并应用高精度锆石 SHRIMP U-Pb 定年,得到东部粗粒斜长角闪岩的年龄为455.1±2.7(2σ)Ma,西部中粒斜长角闪岩的年龄为451.4±5.4(2σ)Ma。因而,确定了它们应该是早古生代晚奥陶世的火成岩,而不是前寒武纪地质体。在西部地段的斜长角闪岩中有一粒捕获锆石的核部得到大约900Ma 的老年龄,正好与该区基底温泉群花岗质片麻岩的年龄大体一致。其微量元素和 Nd-Sr同位素组成特征说明它们形成于岛弧环境。这一研究结果,为研究早古生代时期西天山与俯冲有关的地质事件,以及古亚洲洋的演化提供了新的佐证。The metamorphic rocks of Wenquan Group as Precambrian basement rocks of the West Tianshan orogen occur in the south area of the Wenquan County. Grey amphibolites with middle or coarse texture have been regarded as components of Wenquan Group, those are different entirely from Precambrian fine dark amphibolites in apparent features. Father geological study and highprecision SHRIMP zircon U-Pb dating, the ^206Pb/^238U ages of 455.1±2. 7（2σ） Ma and 451.4±5.4 （2σ） Ma have been gained for these amphibolites from the eastern and western section of Wenquan domain, respectively. So, the results make certain these grey middle-coarse amphibolites in the Wenquan domain are Late Ordovician igneous rocks during the Early Paleozoic, other than Precambrian. One old age of ca. 900Ma was obtained in core of a xenocryst zircon of the amphibolite in the west section of Wenquan, which is approximately consistent with age of basement granitic gneisses of the Wenquan Group. Other evidences of trace elements and Nd-Sr isotopic compositions indicate that the Wenquan Early Paleozoic amphibolites were formed in the island-arc tectonic setting. The results of this study offer new evidence for subduction-related geological events in the West Tianshan and evolution of the Paleoasian Ocean during the Early Paleozoie.

关 键 词：西天山温泉地区 早古生代斜长角闪岩 锆石SHRIMP U—Pb年龄 

分 类 号：P588.34[天文地球—岩石学] P597.3[天文地球—地质学]