晚白垩世特提斯洋盆向华南大陆俯冲:来自桂东南六王石英斑岩的证据  

The Subduction of the Tethyan Ocean Beneath the South China Continent in Late Cretaceous:Evidences from the Liuwang Quartz Porphyry in the Southeastern Guangxi

作　　者：刘兴源 李赛赛[1] 张洪瑞[2] 王秋宇 吴江波 辛良伟 LIU Xing-yuan;LI Sai-sai;ZHANG Hong-rui;WANG Qiu-yu;WU Jiang-bo;XIN Liang-wei(Guangxi Key Laboratory of Hidden Metal Mineral Exploration,Guilin University of Technology,Guilin Guangxi 541004,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]桂林理工大学广西隐伏金属矿产勘查重点实验室,广西桂林541004 [2]中国地质科学院地质研究所,北京100037

出　　处：《矿物岩石地球化学通报》2022年第2期374-387,共14页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：广西自然科学基金资助项目(2018GXNSFAA050016,2020GXNSFAA297091)。

摘　　要：白垩纪华南主要受太平洋构造域的影响,然而近年来的研究发现华南南部白垩纪的岩浆岩可能与新特提斯板块的俯冲作用有关。桂东南地处华南南部太平洋构造域和特提斯构造域的过渡地带,其中广布白垩纪岩浆岩,对这些岩浆岩的细致研究有助于查明华南晚中生代的构造背景。本文对出露于桂东南地区北部六王镇一带的石英斑岩进行了U-Pb年代学和地球化学研究。结果显示,其锆石U-Pb年龄为(98±0.64)Ma,表明其形成于晚白垩世;具有较高的SiO_(2)(75.28%~75.77%)和高K_(2)O(4.90%~6.02%)特征,属过铝质花岗岩类(A/CNK为1.1~1.17);具有轻、重稀土元素分异弱(LREE/HREE为1.14~2.03),Eu负异常明显(δEu≤0.01),富集LILE(Rb、K)及高放射性元素(Th、U、Pb),亏损HFSE(Nb、Zr)等特征。研究样品的锆石ε_(Hf)(t)值为-3.2~-1.6,t_(DM2)为1.25~1.33Ga,指示样品主要来源于中元古代地壳物质的重熔。综合分析认为,六王石英斑岩来源于中元古代泥质岩的部分熔融,形成于晚白垩世早期新特提斯板块向华南大陆俯冲的构造背景。It was generally considered that the South China was mainly affected by the Pacific Tectonic Domain in Cretaceous.However,recent studies have found that the Cretaceous magmatic rocks in the southern South China may be formed in association with the subduction of the Neo-Tethys plate.A large amount of Cretaceous magmatic rocks are widely distributed in the Southeastern Guangxi where is located in the transition zone between the Pacific tectonic domain and the Tethys tectonic domain in the southern South China.A detailed study of these magmatic rocks will help to find out the tectonic setting of the South China in Late Mesozoic.In this paper,a detailed study on the U-Pb chronology and geochemistry of the quartz porphyry exposed in the Liuwang area in the northern part of the southeastern Guangxi has been carried out.The LA-ICP-MS zircon U-Pb age of quartz porphyry is(98±0.64)Ma,indicating that it was formed in the Late Cretaceous.The quartz porphyry belongs to peraluminous(A/CNK=1.1-1.17)granite,as its samples have high contents of SiO_(2)(75.28%-75.77%)and K_(2)O(4.90%-6.02%).The rock is characterized with weak differentiation of LREE and HREE(LREE/HREE=1.14-2.03),obviously negative Eu anomaly(δEu≤0.01),the enrichment of LILE(Rb,K)and high radioactive elements(Th,U,Pb),and depletion of HFSE(Nb,Zr).Theε_(Hf)(t)values(from-3.2 to-1.6)and two stage model ages(1.25-1.33 Ga)of its zircons indicate that it was mainly derived from the remelting of Mesoproterozoic crustal materials.Based on the comprehensice analysis of various kinds of data,it is believed that the quartz porphyry in the Liuwang area was originated from the partial melting of Measoproterozoic argillaceous rocks in the lower crust,and then was formed the tectonic setting of the Neo-Tethys plate subduction to the South China continent in the early stage of Late Cretaceous.

关 键 词：石英斑岩 锆石U-Pb年龄 HF同位素 白垩纪 桂东南 

分 类 号：P588.132[天文地球—岩石学]