| 青藏高原西北缘红其拉莆岩体的岩石成因、时代及其构造意义 |
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| 引用本文： | 康磊,校培喜,高晓峰,朱海平,奚仁刚,过磊,董增产.青藏高原西北缘红其拉莆岩体的岩石成因、时代及其构造意义[J].地质学报,2012,86(7):1063-1076. |
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| 作者姓名： | 康磊 校培喜 高晓峰 朱海平 奚仁刚 过磊 董增产 |
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| 作者单位： | 西安地质矿产研究所, 西安,710054;西安地质矿产研究所, 西安,710054;西安地质矿产研究所, 西安,710054;陕西省地质矿产局地质调查院, 西安,710054;西安地质矿产研究所, 西安,710054;西安地质矿产研究所, 西安,710054;西安地质矿产研究所, 西安,710054 |
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| 基金项目： | 中国地质调查局国土资源大调查研究项目“西昆仑—阿尔金成矿带基础地质综合研究”（No. 1212011085034）、国家自然科学基金 (No. 41002020)和陕西省自然科学基金(No. 2011JQ5008) |
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| 摘 要： | 青藏高原西北缘的南羌塘地块(班公湖-怒江结合带西段北侧)中发育着规模巨大的白垩纪花岗岩带,红其拉甫岩体是该花岗岩带中典型岩体之一,主要由花岗闪长岩和少量闪长岩组成。结合锆石阴极发光(CL)图像和Th、U、REE元素特征,利用LA-ICP-MS锆石U-Pb定年,测得岩体年龄为107.2±0.9Ma,属于早白垩世晚期。地球化学特征显示,岩体偏中性,富Al、Ca和K,稀土元素含量低,轻重稀土分馏明显,中等或弱的负铕异常,富集大离子亲石元素(Rb、Th、K和LREE),亏损高场强元素(Nb、Ta、P、Ti和HREE),属于高钾钙碱性准铝质—弱过铝质I型花岗岩。在岩浆演化过程中,部分熔融与结晶分异作用均起重要作用,并发生了以斜长石、磷灰石和钛铁矿为主的分离结晶作用。岩体的CaO、CaO/Na2O值较高,Nb、Ta亏损、Mg#值较小、相对富钾以及Sr同位素等特征说明岩体源岩应来自下地壳角闪岩相的变玄武岩。根据岩体较低的Y、HREE含量和较高的Al2O3、Sr、Sr/Y比值,发育石英与碱性长石的交生结构,以及SiO2对Mg#和Al2O3图解,推测岩浆源区压力>1.5GPa(地壳厚度至少50km),通过对锆石饱和温度的计算和锆石结构、U-Pb同位素分析,得出岩体初始岩浆温度>788℃,这与高Sr低Yb型花岗岩(埃达克岩)的形成温压条件一致,残留相应为石榴子石+角闪石+金红石(无斜长石)。综合区域地质资料分析,该岩体应是与班公湖-怒江洋闭合有关的冈底斯地块与羌塘地块之间的碰撞造山,导致地壳加厚的产物,表明班公湖-怒江洋西部与中东部的闭合时限可能具有一致性。
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| 关 键 词： | 青藏高原西北缘 红其拉甫岩体 锆石U-Pb年龄 岩石成因 构造意义 |
| 收稿时间： | 2011/9/16 0:00:00 |
| 修稿时间： | 2012/2/28 0:00:00 |
The origin and age of the Hongqilapu pluton and its tectonic significances in northwestern Tibetan Plateau |
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| KANG Lei,XIAO Peixi,GAO Xiaofeng,ZHU Haiping,XI Rengang,GUO Lei and XI Rengang.The origin and age of the Hongqilapu pluton and its tectonic significances in northwestern Tibetan Plateau[J].Acta Geologica Sinica,2012,86(7):1063-1076. |
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| Authors: | KANG Lei XIAO Peixi GAO Xiaofeng ZHU Haiping XI Rengang GUO Lei and XI Rengang |
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| Institution: | KANG Lei 1),XIAO Peixi 1),GAO Xiaofeng1),ZHU Haiping2),XI Rengang1), GUO Lei 1),DONG Zhengchan1) 1)Xi′an Institute of Geology and Mineral Resources,Xi′an,710054; 2)Shaanxi Province Institute of Geological Survey,Xi′an,710054 |
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| Abstract: | South Qiangtang massif in the northwestern Tibetan Plateau(north of western Bangonghu-Nujiang suture)hosts a huge Cretaceous grantie belt,in which the Konjirap pluton is one of typical granitoids.It consists mainly of granodiorite and minor diorite.Combined with the cathodoluminescence(CL)images and element(Th,U and REE)features of zircon,this study yielded an age of 107.2±0.9Ma for the pluton using the LA-ICP-MS zircon U-Pb dating,indicating a late Early Cretaceous.The geochemical analysis shows that the pluton belongs to intermediate rock,characterized by high Al,Ca and K,low ΣREE,distinct REE fractionation,and moderate or weakly negative Eu anomaly,enrichment of LILE (Rb,Th,K,LREE),and depletion of HFSE(Nb,Ta,P,Ti,HREE).All the features suggest a high K calc-alkaline I type granite with metaluminous to slightly peraluminous.Partial melting and crystalline differentiation played a vital role in process of magma evolution,accompanied with separationcrystallization of plagioclase,apatite and ilmenite.The high CaO,high CaO/Na2O ratio,depletion of Nb and Ta,low Mg#,enriched K,and Sr isotope all show that the pluton was dervided from remelting of the amphibole facies basaltic rocks in lower crust.The low Y and HREE,high Al2O3and Sr,and low Sr/Y ratio,and the diagrams of SiO2-Mg#,SiO2-Al2O3,along with the structure of intergrowth between quartz and alkali feldspar,indicate that the pressure of the source region may be>1.5GPa(the thickness of crust was 50km at least).The initial temperature of magma was >788℃ using calculation of the saturation temperatures and structure,and U-Pb isotopes analysis of zircon,and is in accordance with the temperature and pressure conditions of formation of the granite with high Sr and low Yb(adakite),and the residual facies is correspondingly garnet+amphibole+rutile(with no plagioclase).Based on the regional geological data,the pluton should be the product of thickening crust which was caused by the collision between Gangdese massif and Qiangtang massif with the closing of Bangonghu-Nujiang ocean,it is suggested that the closure times of western and central eastern Bangonghu-Nujiang ocean should be the same. |
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| Keywords: | Hongqilapu pluton Northwestern Tibetan Plateau petrogenesis zircon U-Pb geochronology tectonic significances |
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