东天山石炭纪雅满苏组火山岩特征及地质意义  

Geochronology and geochemistry of volcanic rocks from the Yamansu Formation in eastern Tianshan Mountains and their tectonic implications

作　　者：王雯[1] 夏芳[1] 柴凤梅[1] 吴生军[2] 李强[3] 耿新霞[3] 孟庆鹏[4] WANG Wen XIA Fang CHAI Feng-mei WU Sheng-jun LI Qiang GENG Xin-xia MENG Qing-peng(Xinjiang Key Laboratory for Geodynamic Processes and Metallogenic Prognosis of the Central Asian Orogenic Belt, Xinjiang University, Urumqi 830049, China No. 1 Geological Party, Xinjiang Bureau of Geology and Mineral Resources, Urumqi 831100, China MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China Xinjiang Mineral Experiment Research Institute, Urumqi 830000, China)

机构地区：[1]新疆大学新疆中亚造山带大陆动力学与成矿预测实验室,新疆乌鲁木齐830049 [2]新疆地质矿产勘查开发局第一地质大队,新疆昌吉831100 [3]中国地质科学院矿产资源研究所国土资源部成矿作用与资源评价重点实验室,北京100037 [4]新疆地质矿产勘查开发局矿产实验研究室,新疆乌鲁木齐830000

出　　处：《岩石矿物学杂志》2016年第5期768-790,共23页Acta Petrologica et Mineralogica

基　　金：国家重点基础研究发展计划"973"资助项目(2012CB416803);国土资源部公益性行业科研专项经费资助项目(201211073-03)~~

摘　　要：雅满苏组火山岩是东天山石炭纪火山岩的重要组成部分，也是东天山地区海相火山岩型铁多金属矿床的赋矿地层。其年代学及地球化学研究对探讨该区古生代构造演化和火山岩型铁多金属矿床成因具有重要意义。本文对东天山地区雅满苏组火山岩的岩石学、地球化学和同位素年代学进行了系统研究。结果显示：雅满苏组是一套海相火山岩夹碳酸盐岩建造，其上亚组英安岩的LA—ICP—MS锆石UPb年龄为334．4±1．7Ma（MSWD=0．67），代表了雅满苏上亚组火山岩形成时代，切穿雅满苏铁矿区矽卡岩及矿体的正长岩的LA-ICP—MS锆石U．Pb年龄为325．5±1．7Ma（MSWD=0．34），表明雅满苏铁矿床形成不晚于325Ma。雅满苏上亚组英安岩和玄武岩显示了富集LREE、U、Sr，相对亏损Nb、Ta等元素的特征，且英安岩锆石的（176Hf／177Hf）；比值介于0．282644～0．282802之间，εHf（334Ma）为3．0～8．0，表明它们是活动大陆边缘弧环境的产物，英安岩是新生地壳物质部分熔融的结果，玄武岩是软流圈地幔与受俯冲板片流体交代地幔的混合熔体演化的产物。结合前人研究成果，认为雅满苏组火山岩是早石炭世中期古亚洲洋俯冲作用的产物，石炭纪时期古亚洲洋尚未闭合，雅满苏铁矿床形成介于334～325Ma之间，是与石炭纪火山岩有成因联系的铁矿床。The Yamansu Formation, outcropped along the Aqishan-Yamansu belt, is a Late Paleozoic stratigraphic unit that hosts many important iron metallogenetic deposits in eastern Tianshan orogenic belt, Xinjiang. The Yamansu Formation consists of intercalated volcanic and sedimentary rocks. LA-ICP-MS U-Pb analyses of zircons from dacite in the upper part of the Yamansu Formation and syenite cutting across the skarns and iron orebodies in the Yamansu iron deposit area yielded weighted mean 206pb/238U ages of 334.4± 1.7 Ma （MSWD= 0.67） and 325.5 ± 1.7 Ma （MSWD= 0.34）, respectively. These ages indicate that the Yanmnsu Formation was formed during the early Carboniferous and the Yanansu iron ombodies and mineralizations preferentially occurred between 334 and 325 Ma. Geochemically, the ＆cite displays typical arc-like magraatic rocks characteristics, e.g., enrichment of large ion lithophile elements （LILE） and light rare earth element （LREE）, strong negative anomalies of Nb, Ta and Ti with positive εHf （ t ） values （ ＋ 3.0 to ＋ 8.0）, and relatively young Hf crustal model ages. They were probably derived from the dehydration melting of juvenile crustal materials with minor mantle melting and underwent fractional crystallization during the upward migration of magma. The basalts resemble dacites in enrichment of LREE, U and Sr and depletion of Nb, Ta, Zr and Hf, and were probably derived from depleted mantle and mantle wedge modified by fluids from subducted materials. The regional geology and geochemical evidence indicate that the Yamansu Formation volcanic rocks were formed during the early Carboniferous in an active continental margin arc tectonic setting, indicating that the Paelo-Asia Ocean had not been closed. The Yamansu Fe deposit hosted in the Yamansu Formation was formed during 334- 325 Ma, closely associated with Late Paleozoic volcanism.

关 键 词：雅满苏组 火山岩 LA-ICP—MS锆石定年 地球化学 东天山 

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