欢迎访问现代地质!

现代地质 ›› 2022, Vol. 36 ›› Issue (03): 796-811.DOI: 10.19657/j.geoscience.1000-8527.2022.016

• 岩石学 • 上一篇    下一篇

青海南山当家寺花岗岩体与晚三叠世脉岩及其对早中生代构造环境的约束

杨延伟1(), 卢欣祥2(), 王丽伟1, 杨一1, 杨崇科1, 黄凡3   

  1. 1.河南省资源环境调查一院,河南 郑州 450000
    2.河南省自然资源科学研究院,河南 郑州 450053
    3.中国地质科学院矿产资源研究所,北京 100037
  • 收稿日期:2021-07-08 修回日期:2021-12-18 出版日期:2022-06-10 发布日期:2022-07-19
  • 通讯作者: 卢欣祥
  • 作者简介:卢欣祥,男,教授,1938年出生,地质工程专业,主要从事秦岭花岗岩及成矿规律研究。Email: luxx1938@163.com
    杨延伟,男,硕士,工程师,1986年出生,地质工程专业,主要从事矿床学、岩石地球化学研究。Email: yyw198677@126.com
  • 基金资助:
    河南省(外)地质勘查基金项目(〔2016〕46号)

Dangjiasi Granite Complex and Late Triassic Dykes in Qinghai Nanshan Tectonic Zone, and Its Constraints on the Early Mesozoic Tectonic Environment

YANG Yanwei1(), LU Xinxiang2(), WANG Liwei1, YANG Yi1, YANG Chongke1, HUANG Fan3   

  1. 1. The First Institute of Resources and Environmental Investigation of Henan, Zhengzhou,Henan 450000, China
    2. Scientific Academy of Natural and Resources of Henan, Zhengzhou,Henan 450053, China
    3. Institute of Mineral Resources, CAGS, Beijing 100037, China
  • Received:2021-07-08 Revised:2021-12-18 Online:2022-06-10 Published:2022-07-19
  • Contact: LU Xinxiang

摘要:

当家寺花岗岩体是青海南山印支期花岗岩带中东部较大的一个岩体,形成于早三叠世(243.5±2.9 Ma、247.2±1.7 Ma)—中三叠世(240.1±2.1 Ma、241.0±2.6 Ma)。岩体内发育有众多的中-酸性脉岩,岩石类型主要为闪长玢岩、石英闪长玢岩、花岗斑岩等,本研究获得闪长玢岩脉LA-MC-ICP-MS锆石U-Pb年龄为(235.6±2.4 Ma),表明其形成于晚三叠世早期,稍晚于当家寺岩体侵位时限。脉岩作为一种浅成侵入体,其与当家寺花岗岩体分布的构造位置相似,矿物组成及地球化学特征具有近似的特点,说明二者岩石成因及构造背景类似,可能为同一源区壳-幔岩浆混合作用的产物。岩石地球化学分析表明中性脉岩SiO2含量低(54.68%~64.75%),酸性脉岩SiO2含量高(66.00%~77.13%),二者都具高铝(Al2O3=12.24%~17.11%)、高钾钙碱性准铝质-弱铝质的特点(A/CNK=0.85~1.04),具有典型的岛弧花岗岩和碰撞花岗岩的特征。脉岩富集LREE、Rb、Th、K,亏损HREE、Nb、Ta、P、Ti、Ba,(La/Yb)N=5.05~17.61,表现出中等强度Eu的负异常。综合分析认为,脉岩形成于晚三叠世共和裂谷闭合碰撞造山后构造环境由挤压向板内稳定-伸展的变迁阶段,指示晚三叠世早期共和盆地周缘已进入后碰撞的陆内环境。

关键词: 中-酸性脉岩, 锆石U-Pb定年, 地球化学, 当家寺岩体, 晚三叠世, 青海南山

Abstract:

The Dangjiasi granite complex is a larger pluton in the central-eastern part of the Indosinian Nanshan granite belt(Qinghai Province). The complex was emplaced in the Early Triassic (243.5±2.9 Ma,247.2±1.7 Ma)-Middle Triassic (240.1±2.1 Ma,241.0±2.6 Ma). There are many intermediate felsic dykes in the intrusion, comprising mainly diorite porphyry, quartz diorite porphyry, and granite porphyry, LA-MC-ICP-MS zircon U-Pb dating on the diorite porphyry dyke yielded early Late Triassic age (235.6±2.4 Ma), slightly younger than the minimum emplacement age limit of the Dangjiasi granite complex. As a shallow intrusive body, the dykes are similar to the Dangjiasi intrusion in structural setting, and their mineral and geochemical compositions have similar characteristics, indicating that the two rock types have similar genesis and tectonic background, and may have had the same crust-mantle mixed magma source region. Litho-geochemistry shows that the intermediate dykes have low SiO2(54.68%-64.75%), whilst the felsic dykes have high SiO2(66.00%-77.13%), and both have high Al2O3(12.24%-17.11%). The rocks are high-kcalc-alkaline metaluminous-weakly peraluminous (A/CNK=0.85-1.04), with typical island arc granite and collision granite affinities. The rocks are enriched in LREE, Rb, Th and K, but depleted in HREE, Nb, Ta, P, Ti and Ba with (La/Yb)N=5.05-17.61 and medium negative Eu anomaly. Comprehensive analysis suggests that the dykes were formed in the Late Triassic Gonghe rift-closure related collisional orogeny. The tectonic setting changed from compression to intraplate stability-extension, suggesting that the Gonghe Basin(and surroundings) had entered post-collision intracontinental environment in the early Late Triassic.

Key words: intermediate-felsic dyke, zircon U-Pb dating, geochemistry, Dangjiasi complex, Late Triassic, Nanshan, Qinghai Province

中图分类号: