西北天山吐拉苏盆地火山岩SHRIMP年代学和微量元素地球化学研究  

Study on trace elements geochemistry and SHRIMP chronology of volcanic rocks in Tulasu Basin,Northwest Tianshan.

作　　者：安芳[1] 朱永峰[1] 

机构地区：[1]北京大学地球与空间科学学院造山带与地壳演化教育部重点实验室,北京100871

出　　处：《岩石学报》2008年第12期2741-2748,共8页Acta Petrologica Sinica

基　　金：国家科技支撑计划重点项目资助成果(2006BAB07B08)

摘　　要：吐拉苏盆地位于西北天山西段,盆地中大面积出露晚古生代火山—沉积岩地层,该地层的火山—沉积岩是区内阿希、京希—伊尔曼德金矿的主要赋矿围岩,由凝灰岩、流纹岩、安山岩和少量玄武岩组成。对火山岩剖面下部流纹岩中锆石开展的 SHRIMP 年代学研究表明,火山喷发开始的时间早于386Ma(中泥盆世晚期)。因此,下石炭统地层单位"大哈拉军山组"不再适合代表吐拉苏盆地中广泛出露的这套火山—沉积岩地层,本文建议创建中—上泥盆统"伊尔曼德组"。京希—伊尔曼德金矿区及其外围火山熔岩富集大离子亲石元素和轻稀土元素,亏损 Nb、Ta、Zr 和 Hf 等高场强元素,具有典型大陆岛弧火山岩的地球化学特征。因此,吐拉苏盆地晚古生代火山岩代表北天山洋洋壳向伊犁板块俯冲过程中形成的火山岛弧,该岛弧的演化至少持续到晚泥盆世晚期(～363Ma)。受俯冲带流体交代的地幔楔是吐拉苏岛弧火山岩(玄武岩和安山岩)的岩浆源区,大量流纹岩应该是大陆地壳物质熔融的产物。Tulasu Basin, locating in western part of Northwest Tianshan, is mainly composed of Late Paleozoic volcanic-sedimentary rocks and Ordovician limestone. Study on zircon SHRIMP chronology of rhyolite shows that volcanism in Tulasu Basin began a little earlier than 386Ma and continued until - 363Ma. ＂Dahalajunshan＂ Formation representing the Lower Carboniferous stratigraphic unit thus is unreasonable to be used in Tulasu Basin. ＂Yelmand＂ Formation is proposed to name these Middle-Late Devonian volcanicsedimentary strata Volcanic rocks in Tulasu Basin are enriched in LILE and LREE, and depleted in Nb, Ta, Zr and Hf, suggested an island arc environment. North Tianshan Ocean existed at least until Late Devonian （ - 363Ma）. Partial melting of the mantle wedge metasomatized by subduction fluid generated the island arc magma （for basaltic and andesitic rocks）. Rhyolite was probably originated from melting of continental crust.

关 键 词：锆石SHRIMP 岛弧火山岩 吐拉苏盆地 西天山 新疆 

分 类 号：P588.141[天文地球—岩石学] P597.3[天文地球—地质学]