| 班公湖中特提斯洋打开的时限:来自MOR型辉长岩的年代学制约 |
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| 引用本文： | 秦雅东,李德威,刘德民,李华亮.班公湖中特提斯洋打开的时限:来自MOR型辉长岩的年代学制约[J].大地构造与成矿学,2017,41(6). |
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| 作者姓名： | 秦雅东 李德威 刘德民 李华亮 |
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| 作者单位： | 1. 中国地质调查局成都地质调查中心,四川成都,610081;2. 中国地质大学(武汉)地球科学学院,湖北武汉,430074 |
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| 基金项目： | 中国地质调查局西藏1:50000聂拉木等4幅区域地质调查项目，中国地质调查局西藏阿木雄地区地质矿产综合调查项目 |
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| 摘 要： | 班公湖?怒江结合带西段班公湖地区蛇绿岩组合较为完整,由超镁铁质岩、镁铁质堆晶岩、辉绿岩脉、铁镁质熔岩、放射虫硅质岩等组成。这套蛇绿岩所代表的洋盆打开时间一直争论不休。该蛇绿岩中MOR型辉长岩的LA-ICP-MS锆石U-Pb定年显示,18个测点的~(206)Pb/~(238)U加权平均年龄为231.5±2.6 Ma,代表了辉长岩的结晶年龄。地球化学分析表明辉长岩SiO_2含量在46.12%~47.85%之间,TiO_2(1.52%~1.71%),具低的K_2O(0.19%~0.25%)、Al_2O_3(12.97%~13.51%)和Fe_2O_3/FeO比值(0.19~0.24);微量元素蛛网图与洋中脊玄武岩类似,Zr、Nb、Ta、Hf丰度与N-MORB相当或略高,相对富集Ba、Pb、Sr等大离子亲石元素,无Ta-Nb负异常,在基性岩构造环境判别图上显示出洋脊玄武岩的亲合性;REE配分曲线具有平缓型特点,介于E-MORB与N-MORB之间;各种地球化学特征与洋脊玄武岩类似,表明该辉长岩是在班公湖洋盆扩张阶段形成的。结合前人研究成果,本文认为班公湖中特提斯洋盆初始打开时间至少为中三叠世。
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| 关 键 词： | 蛇绿岩 MOR型辉长岩 洋盆初始裂解 班公湖中特提斯 |
Opening Time of Middle Tethys Oceanic Basin: Constrained from Zircon U-Pb Dating of MOR-type Gabbro in Bangong Lake Ophiolite |
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| QIN Yadong,LI Dewei,LIU Demin,LI Hualiang.Opening Time of Middle Tethys Oceanic Basin: Constrained from Zircon U-Pb Dating of MOR-type Gabbro in Bangong Lake Ophiolite[J].Geotectonica et Metallogenia,2017,41(6). |
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| Authors: | QIN Yadong LI Dewei LIU Demin LI Hualiang |
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| Abstract: | A complete ophiolite profile outcrops in the Bangong Lake area in the western part of the Bangong-Nujiang ophiolite zone. The Bangong Lake ophiolite is composed of ultramafic rocks, mafic cumulates, diabase dikes, mafic lavas, and aradiolarian-bearing cherts. LA-ICP-MS U-Pb dating of zircons from MOR-type gabbro in the ophiolite yielded a weighted mean206Pb/238U age of 231.5±2.6 Ma, which represents the crystallization age of the gabbro. The gabbro shows relatively low contents of SiO2(46.12%?47.85%), TiO2 (1.52%?1.71%), K2O (0.19%?0.25%), Al2O3 (12.97%?13.51%) and Fe2O3/FeO ratio (0.19?0.24). The trace element features of the gabbro are similar to those of the mid-ocean ridge basalts, N-MORB in particular, characterized by enriched large-ion lithophile elements (such as Ba, Pb and Sr) and no obvious Ta-Nb anomalies. The geochemical similarity between the gabbro and the mid-ocean ridge basalt indicates that the ophiolite was likely formed in a mid-ocean ridge setting, and therefore, we argue that the opening of Middle Tethys Ocean at the Bangong Lake area was initiated in the Middle Triassic. |
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| Keywords: | ophiolite MOR-type gabbro initial breakup of oceanic basin Bangong Lake Middle Tethys Ocean |
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