帕米尔地区穆尔尕布辉长岩-闪长岩的成因:锆石U-Pb年龄、Hf同位素及岩石地球化学证据

发布时间：2018-05-01 09:13

本文选题：帕米尔 + 穆尔尕布岩体　；参考：《中国地质》2017年04期

【摘要】：穆尔尕布岩体位于塔吉克斯坦帕米尔地区中部,中帕米尔和南帕米尔之间的Rushan-Pshart缝合带中,岩石类型主要由辉长岩和少量闪长岩组成,呈岩株状侵入于新元古代(?)萨雷吉尔加组浅变质碎屑岩中。根据LA-ICPMS锆石U-Pb定年结果,穆尔尕布岩体中辉长岩的年龄为(232.0±1.5)Ma,闪长岩的年龄为(231.5±1.9)Ma,两者在误差范围内一致,代表了该岩体的形成时代。辉长岩和闪长岩中锆石的εHf(t)值变化范围分别为4.8~12.1、6.4~10,加权平均值为8.1±1.5(MSWD=6.5)和7.9±0.8(MSWD=2.4),显示其原岩来源于地幔物质,其单阶段Hf模式年龄TDM1分别为477~621 Ma,391~672 Ma,指示其原岩为寒武纪—前寒武纪基底。岩石地球化学研究表明,辉长岩类具有贫碱、低Al、富Mg特征,属于低钾(拉斑)系列,闪长岩类则显示富Si、Al,贫Mg、低Ti的特征,属于钙碱性-高钾钙碱性系列;两者的稀土和微量元素特征相似,稀土总量高,呈轻稀土富集的右倾型配分型式,无Eu异常或轻微正Eu异常,微量元素富集大离子亲石元素,亏损高场强元素,指示穆尔尕布岩体可能形成于岛弧环境。综合区域地质资料,认为在晚三叠世Rushan洋陆俯冲尚未结束,表明洋盆闭合时限晚于232 Ma。
[Abstract]:The Murgarab body is located in the Rushan-Pshart suture zone between the Middle Pamir and the South Pamir in Tajikistan. The rock type is mainly composed of gabbro and a small amount of diorite, which intruded into the Neoproterozoic in the form of a rock plant. In the shallow metamorphic clastic rocks of the Sarejilga formation. According to the LA-ICPMS zircon U-Pb dating results, the ages of gabbro and diorite are 232.0 卤1.5Maand 231.5 卤1.9Ma. both of them are consistent within the error range and represent the age of formation of the body. The variation range of zircon 蔚 Hfft in gabbro and diorite is 4.812.1 / 6.4kW (weighted average 8.1 卤1.5 MSWDU 6.5) and 7.9 卤0.8MSWDU (2.4g), respectively, indicating that the source rocks originated from mantle material, and their single-stage HF model age TDM1 is 4777221 Ma391M 672 Ma, indicating that the protects are Cambrian-Precambrian basement. The results show that the zircon is derived from mantle material and its age of one-stage HF model is 4770.21 Ma-391mg / 672 Ma., indicating that the source rocks are Cambrian-Precambrian basement. The petrogeochemical study shows that gabbro is characterized by alkali-poor, low-Al-rich and Mg-rich, and belongs to low-K series, while diorite is characterized by rich Si-Al, poor Mgand low Ti, and belongs to calc-alkaline-high-potassium calc-alkaline series. Their rare earth elements and trace elements are similar, the total amount of rare earths is high, and they are in the right dip pattern of light rare earth enrichment. There is no EU anomaly or slight positive EU anomaly, and trace elements are enriched in large ion lithophile elements and depleted in high field strength elements. It indicates that the Murgarab rock may be formed in the island arc environment. Based on the regional geological data, it is considered that the Rushan oceanic subduction was not over in the late Triassic, indicating that the closure time of the oceanic basin was later than 232 Ma.
【作者单位】：中国地质科学院;中国地质调查局西安地质调查中心;
【基金】：中国地质调查局项目(121201112036、12120114018601)资助~~
【分类号】：P588.12

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