今天是2018年10月18日

东昆仑哈拉森地区花岗岩类岩石成因及地质意义

DOI:10.3799/dqkx.2018.716

作者:何成,王力圆,田立明,徐净

联系地址:中国地震局地震研究所,地震预警湖北省重点实验室,湖北武汉 430071

摘要:哈拉森地区位于东昆仑东段,分布着大量花岗岩,对其研究不仅有助于认识东昆仑造山带在晚古生代-早中生代的构造-岩浆演化历史,而且可以为东昆仑古特提斯洋俯冲时限及洋盆闭合时限提供约束.对区内花岗岩进行了岩石学、年代学以及岩石地球化学分析,结果表明哈拉森地区的钾长花岗岩和细粒二长花岗岩锆石LA-ICP-MS U-Pb年龄分别为239.2± 1.7 Ma(MSWD=0.19)和232.4±1.2 Ma(MSWD=0.76),属中三叠世花岗质岩浆作用的产物.岩石主微量元素分析显示该地区花岗岩具有高硅铝、富碱和低钛特征,属于高钾钙碱性到钾玄岩系列的过铝质花岗岩,富集轻稀土元素(LREE)及K、Th、Rb等大离子亲石元素(LILE),明显亏损Nb、Ti、P、Ta等高场强元素(HFSE),具有非常明显的Eu负异常( δ Eu为0.27~0.65).哈拉森地区花岗岩具有高分异I型花岗岩的特征,是同碰撞背景下幔源岩浆与其诱发地壳物质熔融产生的长英质岩浆在地壳深部混合,随后这一混合岩浆又经过高程度的分异演化形成的,进一步证明东昆仑古特提斯洋的俯冲作用一直持续到早三叠世,至中三叠世才逐渐转入陆内碰撞造山阶段.

关键字:花岗岩;地质年代学;地球化学;哈拉森;东昆仑

Petrogenesis and Geological Implications of Granitoids from Halasen, East Kunlun

Author:He Cheng, Wang Liyuan, Tian Liming, Xu Jing

Author Address:Hubei Key Laboratory of Earthquake Early Warning, Institute of Seismology, China Earthquake Administration, Wuhan 430071, China

Abstract:A large amount of granites widely distributes in Halasen area in the East Kunlun Mountains. The study of the granites not only help us to understand the tectono magmatic evolution history of East Kunlun orogenic belt in the Late Paleozoic and Early Mesozoic, but also provides constraints for the subduction and closed time limit of the Paleo-Tethys Ocean. In this paper, we constrain geochronology and petrogenesis of the Halasen granites by zircon U-Pb dating and geochemical analyses. The LA-ICP-MS U-Pb analyses show that the formation ages of K-feldspar granite and fine-grained monzogranite are 239.2±1.7 Ma (MSWD=0.19) and 232.4±1.2Ma (MSWD =0.76), respectively, which are the products of the Middle Triassic granitic magmatism. The geochemistry data show that granites are high-potassium calcalkaline-shoshonite, peraluminous rock which is characterized by high silicon and aluminum, enriched alkali, low titanium, as well as enriched light rare earth elements (LREE) and large ion lithophile elements (LILE, e.g., K, Th and Rb), and depleted in high field-strength elements (HFSE, e.g., Nb, Ti, P, and Ta) with obvious Eu negative anomaly (the value of δ Eu is between 0.27 and 0.65). Halasen granites belong to highly fractionated I-type granite. It is suggested that the Halasen granites were most likely derived from parental magma by mixing of depleted mantle-derived magma and induced crustal-melted felsic magma in the deep crust,and then suffered further differentiation during magma ascent. The subduction of the East Kunlun Paleo-Tethys Ocean lasted to the Early Triassic, and the Middle Triassic witnessed the intracontinental collision.

Keyword:granite; geochronology; geochemistry; Halasen; East Kunlun

 

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作者简介:何成(1989-),男,硕士研究生,主要从事矿床学及矿床地球化学研究方向.ORCID: 0000-0001-6414-2604. E-mail: 466283455@qq.com

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