湖南桃江地区印支期辉绿岩成因——地球化学、年代学和Sr-Nd-Pb同位素约束

金鑫镖; 王磊; 向华; 刘重芃; 段桂玲; 李子云

湖南桃江地区印支期辉绿岩成因——地球化学、年代学和Sr-Nd-Pb同位素约束

Petrogenesis of diabase from Jiangshiqiao in Taojiang City, Hu'nan Province:Constrains from geochemistry, geochronology and Sr-Nd-Pb isotopes

摘要

摘要: 对湖南桃江地区江石桥辉绿岩进行了LA-ICP-MS锆石U-Pb定年，获得的岩浆侵位年龄为229±2.3Ma（n=8，MSWD=1.8，2σ）。其低钾（K₂O/Na₂O=0.14~0.16），贫碱（K₂O+Na₂O=2.89%~2.96%），富集大离子亲石元素（Rb、Ba、Th、U），亏损高场强元素（Nb、Ta、Ti），呈轻稀土元素弱富集，无Eu、Ce异常，富集放射性成因Pb，低（⁸⁷Sr/⁸⁶Sr）_i（0.706052~0.706437），较低正ε _Nd（t）（1.54~1.86）的特征，表明岩石来源于下地壳物质和亏损地幔的混合源区。综合前人的研究结果认为，在印支运动造山后的伸展背景下，软流圈上涌导致区域下地壳及部分地幔物质发生熔融，形成辉绿岩岩浆并向上侵位而成。

Abstract: Zircon LA-ICP-MS U-Pb dating for diabase from Jiangshiqiao in Taojiang City of Hu'nan Province yielded an emplace-ment age of 229±2.3Ma (n=8, MSWD=1.8, 2σ).The diabase is characterized by low values of potassium (K₂O/Na₂O=0.14~0.16), and alkali (K₂O+Na₂O=2.89%~2.96%), enrichment of large ion lithophile elements and LREE and depletion of high field strength el-ements, low (⁸⁷Sr/⁸⁶Sr)_i ratios (0.70606~0.70644), low positive ε _Nd(t) values (1.55~1.87) and enrichment of radioactive Pb, suggesting a mixed source of the depleted mantle (DM) and the lower crustal.In combination with previous studies, the authors hold that the di-abase was formed through partial melt of the mantle and lower crustal components by the upwelling asthenosphere during the Indo-sinian post-orogenic lithosphere extension in Hu'nan Province.

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