北阿尔金白尖山地区花岗闪长岩锆石U-Pb定年、Hf同位素组成及其地质意义

发布时间：2018-04-08 21:29

本文选题：红柳沟-拉配泉蛇绿混杂岩带　切入点：花岗闪长岩　出处：《地质学报》2017年05期

【摘要】：白尖山花岗闪长岩位于北阿尔金红柳沟-拉配泉蛇绿混杂岩带东段,呈大套岩株状产出于拉配泉岩群之中。该花岗闪长岩具有较低的SiO_2含量(62.58%～65.05%),富CaO(4.02%～4.98%),铝饱和指数A/CNK1.0(0.89～0.98),富集K、Rb、Ba,亏损Nb、Ta、Zr、Ti,属于准铝质钙碱性岩石系列,具I型花岗岩的特征;其稀土元素∑REE=90.2～137.8μg/g,具有轻重稀土元素分馏明显,轻稀土元素相对富集的特点,具弱的Eu负异常(δEu_N=0.84～0.92)。该岩石变化范围较大的锆石Hf同位素组成(ε_(Hf)(t)=-2.96～7.99)可能与源区物质不充分的岩浆混染有关,结合地球化学特征及其与实验岩石学资料的对比,其形成应为洋壳俯冲时板片脱水诱发下地壳基性岩石部分熔融产生的初始岩浆结晶作用的产物,同时在岩浆侵位过程中还受到上地壳物质(杂砂岩等)的混染。锆石U-Pb年龄为475.2±2.0Ma,结合锆石CL图像具有岩浆环带特征和Th/U值(0.30～0.75),推断该年龄为花岗闪长岩的形成年龄。综合区域地质背景,本次研究的白尖山花岗闪长岩应为红柳沟-拉配泉蛇绿混杂岩带东部地区早古生代洋壳俯冲岛弧岩浆活动的组成部分,与西部红柳沟地区(恰什坎萨依及巴什考供盆地北缘)的花岗闪长岩和石英闪长岩共同构成北阿尔金早古生代洋壳俯冲产生的岛弧岩浆岩带。此外,由西到东红柳沟-拉配泉蛇绿混杂岩带的南北两侧均发育早古生代与洋壳俯冲有关的花岗质岩石,表明整个北阿尔金洋俯冲时期可能具有双向性。
[Abstract]:Baijianshan granodiorite is located in the eastern segment of the Hongliugou-Lapizan ophiolite melange belt in the northern Altun.The relative enrichment of light rare earth elements is characterized by a weak EU negative anomaly (未 EuS\ + N0. 84 ~ 0. 92).The zircon HF isotopic composition of this rock with a large range of variations (蔚 -Hftn-2.967.99) may be related to the insufficient magmatic mixing in the source area, combined with geochemical characteristics and its comparison with experimental petrological data.Its formation is the product of initial magmatic crystallization caused by partial melting of basic rocks in lower crust induced by plate dehydration during subduction of oceanic crust, and is also mixed by upper crustal materials (complex sandstone, etc.) during magmatic emplacement.The U-Pb age of zircon is 475.2 卤2.0 Ma. Combined with the CL image of zircon, it has the characteristics of magmatic belt and Th/U value of 0.30 ~ 0.75. It is inferred that this age is the age of formation of granodiorite.In view of the regional geological background, the granodiorite studied in this paper should be a component of the early Paleozoic oceanic crust subduction island arc magma in the eastern part of the Hongliugou-Lapiquan ophiolite melange belt.Together with the granodiorite and quartz diorite in the western Hongliugou area (northern margin of the Cashkansayi and Bashkauan basins), the island arc magmatic belt produced by the early Paleozoic oceanic crust subduction in North Altun is formed.In addition, granitic rocks related to oceanic subduction in early Paleozoic have been developed on the north and south sides of the Hongliugou-Lapizan ophiolite melange belt from west to east, indicating that the whole North Altun Ocean subduction period may be bidirectional.
【作者单位】：大陆动力学国家重点实验室西北大学地质学系;
【基金】：国家重点基础研究发展计划项目(编号2015CB856103) 国家自然科学基金项目(编号41430209,41421002) 教育部创新团队(编号IRT1281) 西北大学大陆动力学国家重点实验室自主研究重点课题联合资助成果
【分类号】：P588.12;P597.3

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