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现代地质 ›› 2022, Vol. 36 ›› Issue (03): 848-861.DOI: 10.19657/j.geoscience.1000-8527.2021.064

• 岩石学 • 上一篇    下一篇

内蒙古那仁乌拉早白垩世高分异花岗岩年代学及其成因

李柱1(), 张德会1(), 张荣臻1, 沈存利2, 焦世豪1, 李林2, 朱鹏龙2   

  1. 1.中国地质大学(北京)地球科学与资源学院,北京 100083
    2.内蒙古自治区有色地质勘查局,内蒙古 呼和浩特 010010
  • 收稿日期:2021-02-22 修回日期:2022-05-05 出版日期:2022-06-10 发布日期:2022-07-19
  • 通讯作者: 张德会
  • 作者简介:张德会,男,教授,博士生导师,1955年出生,地球化学专业,主要从事成矿作用地球化学研究。Email: 1978011191@cugb.edu.cn
    李 柱,男,博士研究生,1987年出生,矿物学、岩石学、矿床学专业,主要从事矿床地球化学研究。Email: 867113514@qq.com
  • 基金资助:
    国家自然科学基金项目(41373048);国家自然科学基金项目(41773030);内蒙古自治区地质勘查基金综合研究项目(2020-KY03)

Geochronology and Petrogenesis of the Highly-Fractionated Early Cretaceous Narenwula Granite, Inner Mongolia, China

LI Zhu1(), ZHANG Dehui1(), ZHANG Rongzhen1, SHEN Cunli2, JIAO Shihao1, LI Lin2, ZHU Penglong2   

  1. 1. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
    2. Nonferrous Geological Bureau of Inner Mongolia, Hohhot, Inner Mongolia 010010, China
  • Received:2021-02-22 Revised:2022-05-05 Online:2022-06-10 Published:2022-07-19
  • Contact: ZHANG Dehui

摘要:

内蒙古那仁乌拉地区具有较大的稀有金属找矿潜力,但与成矿有关的那仁乌拉花岗岩体在年代学和成因方面仍存在较多争论。为厘定该花岗岩体成岩年龄及成因类型,对其进行了LA-ICP-MS锆石U-Pb定年和岩石地球化学分析。测年结果表明,中粗粒黑云母二长花岗岩和似斑状二长花岗岩成岩年龄分别为(142.1±1.0)Ma和(142.3±1.2)Ma,指示那仁乌拉花岗岩体为早白垩世岩浆活动的产物,与区域上晚侏罗世—早白垩世花岗岩大规模侵入时代基本吻合。岩石地球化学分析显示,岩体富硅(SiO2含量为73.69%~76.67%)、富碱(Na2O+K2O含量为8.40%~8.80%)和贫铁、镁、钙、磷等;Zr、Hf、Rb、Th等元素明显富集,Ba、Sr、P、Ti等元素强烈亏损,Nb元素相对亏损;稀土元素总量较低,显示较强烈的Eu负异常(δEu=0.20~0.36),轻、重稀土分馏明显(LREE/HREE=6.23~14.28),富集轻稀土;属于弱过铝质高钾钙碱性花岗岩。综合矿物学、岩石学和地球化学特征,判断那仁乌拉花岗岩成因类型应归为高分异I型花岗岩。结合区域构造和地质背景,认为位于华北板块北缘的那仁乌拉花岗岩体形成于早白垩世的板内伸展环境。

关键词: 年代学, 地球化学, 高分异花岗岩, 早白垩世, 内蒙古

Abstract:

A number of rare metal deposits have been discovered in Narenwula area of Inner Mongolia, with high metallogenic potential. However, there are still many controversies about the chronology and genesis of Narenwula granite. LA-ICP-MS zircon U-Pb dating and geochemical analysis have been carried out to determine the age and genetic type of the Narenwula granite. The U-Pb dating results show that the medium-coarse biotite monzogranite and porphyritic monzogranite were emplaced in the Early Cretaceous, at (142.1±1.0)Ma and(142.3±1.2)Ma, respectively. Its diagenetic age is basically consistent with the ages of the extensive regional granite emlacement in the Late Jurassic-Early Cretaceous period. Whole-rock geochemistry shows that the granite is characterized by high silica(SiO2=73.69%-76.67%)and alkali(Na2O+K2O=8.40%-8.80%), but low P2O5, MgO, FeOT, CaO, and REE. The rocks have high LREE/HREE ratios(LREE/HREE=6.23-14.28) and marked negative Eu anomalies (δEu=0.20-0.36). They are obviously enriched in Zr, Hf, Rb, and Th, but strongly depleted in Ba, Sr, P, and Ti, and slightly depleted in Nb. The granite is high-K calc-alkaline and weakly peraluminous. Based on the characteristics of mineralogy, petrology and geochemistry, we concluded that the granite belongs to highly-fractionated I-type. Considering the structural features and regional geological background, we inferred that the Narenwula granite in the northern margin of the North China Plate was formed in the Early Cretaceous within-plate extensional setting.

Key words: geochronology, geochemistry, highly-fractionated granite, Early Cretaceous, Inner Mongolia

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