西天山查岗诺尔和智博铁矿区火山岩地球化学特征、锆石U-Pb年龄及地质意义  

Geochemistry and zircon U-Pb age of volcanic rocks from the Chagangnuoer and Zhibo iron deposits,western Tianshan,and their geological significance

作　　者：蒋宗胜[1] 张作衡[1] 侯可军[1] 洪为[1] 王志华[2] 李凤鸣[3] 田敬全[4] 

机构地区：[1]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 [2]中国地质大学地球科学与资源学院,北京100083 [3]新疆维吾尔自治区地质矿产勘查开发局 [4]新疆维吾尔自治区地质矿产勘查开发局第三地质大队

出　　处：《岩石学报》2012年第7期2074-2088,共15页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划(2012CB416803);国家科技支撑计划(2011BAB06B02);地质矿产调查评价项目(1212011085060)联合资助

摘　　要：西天山东段的查岗诺尔铁矿和智博铁矿赋存于以玄武岩、玄武安山岩、粗面岩以及安山质凝灰岩为主的晚石炭世火山岩中,对火山岩的形成时代以及构造地质背景的研究是重建成矿过程的关键。本文通过对两个矿区的火山岩进行岩石地球化学和LA-ICP-MS锆石U-Pb测年分析来探讨火山岩形成的构造环境与时代。地球化学分析表明大多数火山岩化学成分从钙碱性、高钾钙碱性变化到钾玄岩系列,富集轻稀土元素(LREE)和大离子亲石元素(LILE;如Rb、Th、K),重稀土元素(HREE)配分平坦,同时具有Nb、Ta、Ti的强烈亏损,类似于岛弧火山岩的地球化学特征。大多数玄武质火山岩在构造环境判别图中位于火山弧环境。LA-ICP-MS锆石U-Pb测年显示流纹岩和英安岩的206Pb/238U加权平均年龄分别为301.8±0.9Ma和300.3±1.1Ma。此外,对两件闪长岩样品测年获得206Pb/238U加权平均年龄介于303.8～305Ma之间。火山岩与闪长岩样品具有类似的地球化学特征以及形成时代,表明它们可能来源于同一母岩浆,形成于相同的构造背景下。结合区域地质资料,本文认为矿区内出露的高钾钙碱性到钾玄岩系列火山岩可能属于俯冲过程末期阶段大陆岛弧岩浆作用的产物。The Chagangnuoer and Zhibo iron deposits occurring in eastern segment of western Tianshan, were hosted primarily by the Late Carboniferous volcanic rocks, which mainly contain basalt, basaltic andesite, traehyte and andesitic tuff. The tectonic setting and age of the volcanic rocks are key elements in the reconstruction of ore genesis. In this paper, representative samples of volcanic rocks from the Chagangnuoer and Zhibo iron deposits were analyzed for major, trace elements and zircon U-Pb dating to validate their tectonic setting and formation ages. Geochemical data indicate that most of the volcanic reeks range in composition from talc-alkaline, high-K talc-alkaline to shoshonitic, with light rare earth element（LREE） and large ion lithophile element（ LILE; e. g. , Rb, Th, K） enrichment and almost fiat heavy rare earth element（HREE） patterns as well as strongly negative Nb, Ta and Ti anomalies, similar to features of arc volcanic rocks. In the plots of tectonic discrimination, the basaltic volcanic rocks are mainly projected in are setting regions. LA-ICP-MS U-Pb dating of magmatic zircons from the rhyolite and daeite yield weighted average ^206pb/^238U ages of 301.8 ± 0. 9Ma and 300. 3± 1.1Ma, respectively. In addition, weighted average ^206 pb/^238U ages from 303. 8Ma to 305 Ma were obtained for two diorites. The similar geochemical characteristics and formation ages of volcanic rocks and diorites indicated that they were sourced from the same parent magma and may formed in the same tectonic setting. Combined with the regional geological data, we therefore suggest that the high-K eale-alkaline to shoshonitie volcanic rocks were probably the products of continental island-arc magmatism during the late stage of subduetion.

关 键 词：火山岩 地球化学 锆石U-PB测年 查岗诺尔铁矿 智博铁矿 西天山 

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