广东东源地区青溪复式岩体年代学、地球化学及成因  

Geochronology,geochemistry and genesis of the Qingxi complex pluton in Dongyuan,Guangdong Province

作　　者：叶升明 尼玛央金 郭永山 何翔 彭智敏[3] Ye Shengming;Nyima Yangjin;Guo Yongshan;He Xiang;Peng Zhimin(School of Earth Sciences,East China University of Technology,Nanchang 330000,Jiangxi,China;Guangdong Geological Survey Institute,Guangzhou 510080,Guangdong,China;Chengdu Center,China Geological Survey,Chengdu 610000,Sichuan,China)

机构地区：[1]东华理工大学地球科学学院,江西南昌330000 [2]广东省地质调查院,广东广州510080 [3]中国地质调查局成都地质调查中心,四川成都610000

出　　处：《地质学刊》2024年第2期125-139,共15页Journal of Geology

基　　金：广东省地质勘查与城市地质专项“广东东源地区1∶5万区域地质调查”(2022-17);“广东1∶5万双江圩、义合圩、河源县、柏埔圩幅区域地质调查”(2023-16);“广东1∶5万蓝塘、观音阁区域地质调查”(2023-19)。

摘　　要：通过LA-ICP-MS锆石U-Pb测年、锆石Lu-Hf同位素测试以及岩石主微量元素分析,揭示了广东东源地区青溪复式岩体的两种主要岩性:中细粒(斑状)黑云母二长花岗岩(J_(3)^(1c)ηγ)、粗中粒黑云母二长花岗岩(K_(1)^(3b)ηγ),其加权平均年龄分别为(158.2±1.3)、(112.8±2.9)~(116.1±1.7)Ma,表明青溪复式岩体形成于晚侏罗—早白垩世。该岩体的地球化学特征表现为高硅(SiO_(2)质量分数为74.32%~78.73%)、准铝质—过铝质(A/CNK为0.97~1.08)、高分异(DI为92.55~94.78,Zr/Hf比为17.9~26.3),且富集Rb、Th、U、La、Nd、Sm、Lu和LREE等元素,亏损Ba、Nb、Sr、P和Ti等元素。此外,两期侵入体的Eu值呈明显负异常(δEu分别为0.1、0.1~0.2),Ga/Al比较高(10^(4)Ga/Al比分别为2.68~2.79、2.90~3.79),岩体地球化学特征指示应属高分异铝质A2型花岗岩。εHf(t)为-8.6~6.9,绝大部分为-6.7~-0.3,相应T_(DMC)为0.73~1.76 Ga。综合分析表明,青溪复式岩体形成于燕山晚期古太平洋板块俯冲后撤、地壳减薄的伸展构造环境中,在高温热流的作用下,由地幔与古老的下地壳岩石部分熔融混合形成。By means of LA-ICP-MS zircon U-Pb dating,zircon Lu-Hf isotope testing,and major and trace element analysis,it is revealed that two main lithologic types of the Qingxi complex pluton in Dongyuan area,Guangdong are medium-fine grained(porphyritic)biotite monzonite granite(J_(3)^(1c)ηγ)and coarse medium-grained biotite monzonite granite(K_(1)^(3b)ηγ),whose weighted average ages are(158.2±1.3)Ma and(112.8±2.9)-(116.1±1.7)Ma,respectively,indicating that the Qingxi complex pluton was formed in the Late Jurassic and the Early Cretaceous.Their geochemical characteristics are high silica(SiO_(2)mass fraction is 74.32%-78.73%),quasi-aluminous-peraluminous(A/CNK is 0.97-1.08),high differentiation(DI is 92.55-94.78 and Zr/Hf is 17.9-26.3).They are enriched in Rb,Th,U,La,Nd,Sm,Lu and LREE,and deficient in Ba,Nb,Sr,P and Ti.The Eu values of the two intrusions are obviously negative(δEu is 0.1,0.1-0.2 respectively),and the 10^(4)Ga/Al is high(10^(4)Ga/Al is 2.68-2.79,2.90-3.79).The geochemical characteristics indicate that the Qingxi complex pluton belongs to aluminous A2-type granite with high differentiation.εHf(t)values range from-8.6 to 6.9,with most values ranging from-6.7 to-0.3 and corresponding T_(DMC)ranging from 0.73 to 1.76 Ga.Comprehensive analysis shows that the Qingxi complex pluton was formed in the extensional tectonic environment of the late Yan-shan period when the paleo-Pacific plate subducted and the crust thinned.The Qingxi complex pluton was the product of partial melting of the ancient lower crust and the mantle rock under the high-temperature heat flow.

关 键 词：高分异A2型花岗岩 同位素年龄 地球化学特征 青溪复式岩体 成因 广东东源 

分 类 号：P597.3[天文地球—地球化学] P588.115[天文地球—地质学]