西南天山超高压变质带中志留纪岛弧火山岩岩片及其构造意义  

Silurian arc volcanic slices and their tectonic implications in the southwestern Tianshan UHPM belt,NW China

作　　者：蒲晓菲[1] 宋述光[1] 张立飞[1] 魏春景[1] 

机构地区：[1]教育部造山带与地壳演化教育部重点实验室北京大学地质系,北京100871

出　　处：《岩石学报》2011年第6期1675-1687,共13页Acta Petrologica Sinica

基　　金：国家基础科学发展规划项目(2009CB825007);国家自然科学基金项目(40730314;40821002;40825007)联合资助

摘　　要：西南天山造山带位于伊犁-中天山板块和塔里木板块之间,普遍被认为是古南天山洋闭合,塔里木板块和伊犁-中天山板块碰撞造山的产物。在西南天山含榴辉岩高压-超高压变质带中,我们在哈布腾苏和科普尔特2个地区识别出这一套基性-酸性火山岩。在哈布腾苏剖面,该套火山岩以酸性岩为主,在野外作为构造岩片与高压-超高压榴辉岩与蓝片岩相间产出。在科布尔特剖面,岩石组合包括玄武岩,安山岩,英安岩,流纹岩和石英斑岩,具有多个从基性到酸性的岩浆旋迴,并普遍发生绿片岩相变质,与高压超高压岩石的变质程度有明显差异。大部分岩石具有轻稀土轻度富集,重稀土平坦,高场强元素亏损,大离子亲石元素富集的地球化学特征,属于典型的弧火山岩,与大洋岩石圈板块俯冲有关。锆石SHRIMP年龄为420～427Ma,这是西南天山地区目前已知的最早的岛弧火山岩,对揭示古南天山洋的演化历史和弧陆碰撞过程有重要意义。Southwestern Tianshan is a 1000km orogenic belt between the Ili-Central Tianshan （ICTS） plate and the Tarim plate,believed to be resulted from the collision between Tarim plate and the northern ICTS plate with the consequent closure of the ancient South Tianshan Ocean.A set of arc volcanic rocks was discovered in Habutengsu and Kepuerte in the eclogite-bearing ultrahigh-pressure metamorphic （UHPM） belt of the southwestern Tianshan,occurring as tectonic slices intercalated in the field.Rocks from Habutengsu are mainly rhyolite and quartz porphyries,while those from Kepuerte cross-section,consist of low-grade metamorphosed basalt,andesite,dacite and rhyolite.Geochemical study reveals characteristics of typical arc volcanic sequences with right-declined chondrite-normalized REE patterns and enrichment of LILE and depletion of HFSE as the typical characteristics of normal island arc volcanics.The zircon U-Pb dating by SHRIMP gives ages ranging from 420Ma to 427Ma as the earliest record as known for arc volcanics in southwestern Tianshan.These ages of the arc volcanic rocks suggest that the ancient South Tianshan Ocean began its subduction no later than 427Ma.

关 键 词：岛弧火山岩 志留纪 超高压变质带 西南天山 

分 类 号：P588.14[天文地球—岩石学] P597.3[天文地球—地质学]