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勉略构造带横现河地区张岩沟双峰式火山岩的地球化学特征、LA—ICP—MS锆石U—Pb年龄及其构造意义

ISSN号：1000-3657
期刊名称：《中国地质》
时间：0
分类：P597.3[天文地球—地球化学;天文地球—地质学]
作者机构：[1]长安大学地球科学与资源学院,陕西西安710054, [2]西部矿产资源与地质工程教育部重点实验室,陕西西安710054, [3]中国地质大学北京地球科学与资源学院,北京100083
相关基金：中国地质调查局地质调查项目（1212011120161）、国家自然科学基金项目（41172186,40972136,40572121）、高等学校博士学科点专项科研基金项目（20110205110004）、中央高校基本科研业务专项基金项目（CHD2011TD020）共同资助.

作者：徐通[1], 裴先治[1,2], 李瑞保[1,2], 李佐臣[1,2], 裴磊[3], 刘成军[1], 陈有炘[1], 汪晓伟[1], 杨杰[1], 胡楠[1]

关键词：双峰式火山岩, 大陆裂谷, RODINIA, 张岩沟, 勉略构造带, bimodal volcanic rocks, continental rift, Rodinia, Zhangyangou, Mian-Lue tectonic zone

中文摘要：

横现河地区张岩沟双峰式火山岩位于勉略构造带三岔子一略阳段，由紧密共生的变质基性火山岩和变质中酸性火山岩组成．其原岩为亚碱性玄武岩和亚碱性流纹一英安岩。中酸性火山岩稀土元素含量明显低于玄武岩，表明中酸性火山岩为地壳部分熔融形成．而非分离结晶成因。玄武岩具有较高的zr含量与较高的Zr／Y值，表现出板内玄武岩特征．其具有的弧印记应为陆壳物质混染所致。LA—ICP—MS锆石u—Pb测试结果表明，流纹岩成岩年龄为（728±10）Ma（n=4，MSWD=0．14）。结合区域地质背景，认为张岩沟双峰式火山岩形成于地壳伸展机制下的大陆裂谷环境，预示着该地区新元古代洋盆的打开。这一新成果．对研究勉略带新元古代的构造演化以及探讨扬子地块北缘对Rodillia超大陆裂解的响应具有重要意义。

英文摘要：

Zhangyangou bimodal volcanic rocks are located in Hengxianhe area,Sanchazi-Lueyang segment of Mian-Lue tectonic zone. The bimodal volcanic rocks consist of metamorphosed basic volcanic rocks and metamorphosed acid-intermediate rocks in close association, and the protoliths are sub-alkaline basalt and sub- alkaline rhyolitic-dacite. On account of the higher REE concentrations in basalt than in rhyolitic-dacite, the authors hold that the origin of rhyolitic-dacite was partial melting of the crustal material rather than the fractional crystallization of the basaltic magma. Basic volcanic rocks show the intraplate geochemical characteristics such as high Zr concentrations and Zr/Y ratios, and their marks of arc result from the hybridism of the crustal material. The result of U-Pb isotope dating by means of Laser Ablation Inductively Coupled Plasma Mass Spectrometry makes it clear that the formation age of the rhyolite is （728±10） Ma （n=4, MSWD=0.14）. Combined with the regional geological background, the authors consider that Zhangyangou bimodal volcanic rocks were formed in a continental rift environment under the crust extensional mechanism. The formation of Zhangyangou bimodal volcanic rocks heralded the opening of Neoproterozoic Ocean. This new achievement is of important significance both for the further study of the evolution of Mian-Lue tectonic zone and the breakup of Rodinia supercontinent and other continents on the north margin of the Yangtze block.