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  

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

作　　者：杨延伟 卢欣祥 王丽伟 杨一 杨崇科 黄凡[3] YANG Yanwei;LU Xinxiang;WANG Liwei;YANG Yi;YANG Chongke;HUANG Fan(The First Institute of Resources and Environmental Investigation of Henan,Zhengzhou,Henan 450000,China;Scientific Academy of Natural and Resources of Henan,Zhengzhou,Henan 450053,China;Institute of Mineral Resources,CAGS,Beijing 100037,China)

机构地区：[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

出　　处：《现代地质》2022年第3期796-811,共16页Geoscience

基　　金：河南省(外)地质勘查基金项目(〔2016〕46号)。

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SiO_(2)含量低(54.68%~64.75%),酸性脉岩SiO_(2)含量高(66.00%~77.13%),二者都具高铝(Al_(2)O_(3)=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。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 SiO_(2)(54.68%-64.75%),whilst the felsic dykes have high SiO_(2)(66.00%-77.13%),and both have high Al_(2)O_(3)(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.

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 

分 类 号：P588.1[天文地球—岩石学] P595[天文地球—地质学] P597