| 青藏高原班公湖地区晚白垩世埃达克岩年代学、地球化学及构造意义 |
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| 引用本文： | 张 硕,史洪峰,郝海健,李德威,吝 岩,冯旻譞.青藏高原班公湖地区晚白垩世埃达克岩年代学、地球化学及构造意义[J].地球科学,2014,39(5):509-524. |
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| 作者姓名： | 张 硕 史洪峰 郝海健 李德威 吝 岩 冯旻譞 |
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| 作者单位： | 1.中国地质大学地质调查研究院，湖北武汉 430074 |
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| 基金项目： | 中国地质调查局西藏1∶5万聂拉木等4幅区域地质调查(No.1212011121242);中国地质调查局西藏1∶5万日土县卡易错地区4幅区域地质调查(No.1212011121246) |
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| 摘 要： | 青藏高原西部班公湖地区的日松岩体和甲维酸性岩脉位于班公湖蛇绿混杂岩带南侧，岩石类型为英云闪长岩，花岗闪长玢岩和花岗闪长岩，显示中钾钙碱性-高钾钙碱性过渡的特征.元素地球化学组成表明，岩石均具有埃达克岩特征，表现为高的SiO2(63.05%~70.72%)、高Al2O3(≥15%)、低MgO(0.97%~2.33%)＜3%、高Sr含量(380.4×10-6~625.0×10-6)、Sr/Y(＞35)、低HREE、Y(5.64×10-6~13.80×10-6)和Yb(0.46×10-6~1.25×10-6)，轻重稀土分异明显(17.09＜(La/Yb)N＜48.51).日松花岗闪长岩体LA-ICP-MS锆石U-Pb年龄为82.0±1.1 Ma；甲维近东西走向的花岗闪长岩脉和近南北走向的花岗闪长玢岩脉LA-ICP-MS锆石U-Pb年龄分别为90.7±1.2 Ma和82.9±1.2 Ma.日松和甲维处埃达克岩均富钾贫钠，低Cr、Ni，高Th、Th/La、Th/U、Rb/Sr以及相对低的Sr/Y和高Mg#(43.09~54.35)等特征显示其为玄武质岩浆底侵加厚下地壳部分熔融形成.91~82 Ma的埃达克岩形成于后碰撞初期阶段，为中特提斯洋闭合后板内热隆伸展、壳幔相互作用的产物，可以作为班公湖地区由板块构造体制转向板内构造体制的标志.
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| 关 键 词： | 埃达克岩 地球化学 洋陆转换 加厚下地壳 班公湖 中特提斯洋 |
| 收稿时间： | 2013-08-19 |
Geochronology,Geochemistry and Tectonic Significance of Late Cretaceous Adakites in Bangong Lake,Tibet |
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| Abstract: | Risong rocks and Jiawei acid rock veins are located at Bangong Lake ophiolite mélange belt, western Tibetan Plateau. The lithology is tonalite, corcovadite and granodiorite, displaying a transition from medium-K calc-alkaline series to high-K calc-alkaline series. Rocks show geochemical characteristics of adakites, having high content of SiO2 (63.05%~70.72%), Al2O3(≥15%), Sr (380.4×10-6-625.0×10-6), Sr/Y ratio(> 35) and low content of MgO (0.97%-2.33%) < 3%, HREE, Y(5.64×10-6-13.80×10-6) and Yb(0.46×10-6-1.25×10-6). The differentiation is obvious between HREE and LREE (17.09 < (La/Yb)N < 48.51). Risong granodiorite is dated to 82.0±1.1 Ma by zircon U-Pb dating method; east-west trend granodiorite and south-north trend corcovadite are dated to 90.7±1.2 Ma, 82.9±1.2 Ma respectively. Risong and Jiawei adakitic rocks are enriched in K and depleted in Na, and have low Cr, Ni, Sr/Y and high Th, Th/La, Th/U, Rb/Sr and Mg#(43.09-54.35). These characteristics indicate that they were formed by partial melting of thickened lower crust which was caused by basaltic magma underplating. 91-82 Ma adakites were formed in the early stage after the collision as the product of both interplates thermal upwelling extension and crust-mantle interaction after the closure of Meso-Tethys. Outcropping of adakites in this period can mark the transition from the plate tectonic system to intraplate tectonic system. |
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