| 西藏南木林县拉隆地区花岗闪长岩体的时代、岩石地球化学特征及构造背景 |
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| 引用本文： | 吉雪峰,魏启荣,李世杰,许欢,王旭东,陈泰一,王健,欧波,赵闪,杨长青.西藏南木林县拉隆地区花岗闪长岩体的时代、岩石地球化学特征及构造背景[J].地球科学,2018,43(12):4566-4585. |
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| 作者姓名： | 吉雪峰 魏启荣 李世杰 许欢 王旭东 陈泰一 王健 欧波 赵闪 杨长青 |
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| 作者单位： | 1.中国地质大学资源学院, 湖北武汉 430074 |
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| 基金项目： | 中国地质调查局项目DD20160015 |
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| 摘 要： | 冈底斯印支期构造-岩浆-成矿的研究比较缺乏.以出露在冈底斯隆格尔-念青唐古拉复合古岛弧带的拉隆花岗闪长岩体为研究对象，通过野外地质调查、岩石学、LA-ICP-MS锆石U-Pb定年、岩石地球化学和锆石Lu-Hf同位素等方面的研究，探讨了其岩石成因和形成的构造背景.结果显示，拉隆花岗闪长岩体的LA-ICP-MS锆石U-Pb年龄为223.5±3.9 Ma~225.4±4.9 Ma，形成于晚三叠世（T3），属印支晚期构造-岩浆活动的产物；花岗闪长岩体表现出低Ti（w（TiO2）=0.46%~0.73%），富Si（w（SiO2）=63.24%~67.94%）、Al（w（Al2O3）=14.14%~15.85%）、Na（w（Na2O）=2.58%~3.04%）、K（w（K2O）=3.06%~4.89%），高钾钙碱性-钾玄岩系列和弱过铝质的主量元素地球化学特征；岩体稀土总量∑REE为138.62×10-6~255.53×10-6，配分模式为轻稀土元素富集的右倾斜型，其（La/Yb）N值为8.35~17.90，具明显的负Eu异常（Eu/Eu*=0.54~0.69），无Ce异常（Ce/Ce*=0.92~1.02）；微量元素表现出Ba、Nb、Ta、Sr、Ti、P元素亏损和Rb、K、Th、U、Zr、Hf元素富集的特征.岩体的εHf（t）为-6.4~2.5，其两阶段模式年龄tDM2为980~1 479 Ma，相当于念青唐古拉群形成的地质时代.拉隆花岗闪长岩体属A型花岗岩，为古老下地壳物质部分熔融的岩浆产物，并有少量地幔物质的加入，形成于古特提斯俯冲碰撞形成的岛弧背景下局部拉张的构造环境.
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| 关 键 词： | 拉隆花岗闪长岩体 锆石U-Pb定年 地球化学 A型花岗岩 构造地质学 |
| 收稿时间： | 2018-07-12 |
Geochronology,Geochemistry and Tectonic Settings of Granodiorite in Lalong Area,Namling, Tibet |
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| Abstract: | The study on the tectono-magmatic mineralization of the Gangdese Indosinian is relatively deficient. This paper takes Lalong granodiorite masses located in the Gangdese Lunggar-Nyainqentanglha tectono-magmatic belt as the research object. The field geological surveying, petrology, LA-ICP-MS zircon U-Pb dating, geochemistry and Hf isotope data are systematically studied to discuss the petrogenesis and tectonic settings. It is found that the LA-ICP-MS zircon U-Pb ages show a weighted average age between 223.5±3.9 Ma and 225.4±4.9 Ma, indicating that they formed in Late Triassic epoch, and they are probably tectonic-magmatic products of late period of Indosinian. The rocks show low Ti(w(TiO2)=0.46%-0.73%), rich in Si(w(SiO2)=63.24%-67.94%), Al(w(Al2O3)=14.14%-15.85%), Na(w(Na2O)=2.58%-3.04%) and K(w(K2O)=3.06%-4.89%), belonging to the high-K calc-alkaline to shoshonite series and weakly peraluminous; enrichment in REE, and the ΣREE is 138.62×10-6 to 255.53×10-6. The rare earth element distribution pattern is the right tilt type of the light rare earth element enrichment, the (La/Yb)N=8.35-17.90, with negative Eu anomaly (Eu/Eu*=0.54-0.69) and without Ce anomaly (Ce/Ce*=0.92-1.02). The rocks show depletion in Ba, Nb, Ta, Sr, Ti and P; enrichment in Rb, K, Th, U, Zr and Hf in the trace elements. The εHf(t)=-6.4-2.5, coinciding with two-phase model age (tDM2) of the crust of 980-1 479 Ma, and a same geologic age with the Nyainqentanglha Group. Lalong granodiorite masses belong to A-type granite. They are partially melted magmatic products induced by ancient lower crust material, and accompanied by a small amount of mantle material. They are formed by the local extension of the tectonic setting in the island arc environment formed by the ancient Tethys subduction. |
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