华南晚三叠世火山岩的识别:对古太平洋洋壳俯冲启动时限的制约  

Identification of Late Triassic volcanic rocks in South China:constraints on the timing initiation of the paleo-Pacific subduction

作　　者：孙杰 刘磊[1,2] 李响[3] 赵增霞 赵阳[1,2] SUN Jie;LIU Lei;LI Xiang;ZHAO Zengxia;ZHAO Yang(Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration,Guilin University of Technology,Guilin 541006,China;Collaborative Innovation Center for Exploration of Nonferrous Metal Deposits and Efficient Utilization of Resources in Guangxi,Guilin University of Technology,Guilin 541006,China;..Wuhan Center of China Geological Survey,Wuhan 430205,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541006 [2]桂林理工大学有色金属矿产勘查与资源高效利用省部共建协同创新中心,广西桂林541006 [3]中国地质调查局武汉地质调查中心,武汉430205

出　　处：《桂林理工大学学报》2023年第1期1-13,共13页Journal of Guilin University of Technology

基　　金：国家自然科学基金项目(42073031,41702056,42263008);广西自然科学基金项目(2021GXNSFAA220077,2021GXNSFBA220063)。

摘　　要：以粤东地区原认定为早侏罗世的嵩灵组中酸性火山岩为研究对象,进行了系统的锆石U-Pb年代学和Lu-Hf同位素分析工作。结果表明:嵩灵组下部3件火山岩形成于204~200 Ma,据此可将华南晚中生代连续活动的火山作用时代前推至晚三叠世。3件样品均具有亏损的锆石Hf同位素组成,其ε_(Hf)(t)值分别为+9.2~+5.7、+5.7~+2.2和+10.0~+2.9,相对于研究区地壳成分明显亏损,暗示该火山岩主要源于古元古代地壳基底物质的重熔,但有明显的亏损幔源物质贡献。结合前人研究结果可知,粤东地区晚中生代火山岩岩石成因中亏损幔源物质贡献的程度,由晚三叠世向中侏罗世逐渐减弱,但随后又逐渐增强。华南晚侏罗世以来的岩浆活动记录了古太平洋洋壳俯冲晚阶段的信息,中侏罗世以前的岩浆活动则是古太平洋洋壳俯冲早阶段的诱发结果。本文识别出的华南晚三叠世火山岩,暗示古太平洋洋壳俯冲作用的起始时间不晚于晚三叠世。Taking the intermediate-acid volcanic rocks of the Songling Formation originally identified as the Early Jurassic in eastern Guangdong as the research object,a systematic chronology and isotopic analysis of U-Pb zircon are carried out.The result shows that the three volcanic rocks in the lower part of the Songling Formation were formed at 204-200 Ma.Therefore,the continuous Late Mesozoic volcanism in South China can bring temporally forward to Late Triassic.All three volcanic samples show depleted zircon Hf isotopic compositions,with ε_(Hf)(t)values varying between+9.2-+5.7,+5.7-+2.2 and+10.0-+2.9,respectively.It suggests that the volcanic rocks were derived by partial melting of the Paleoproterozoic crustal basement,with obvious depleted mantlederived involvement.According to the results of previous studies,the contribution of depleted mantle-derived materials in the genesis of Late Mesozoic volcanic rocks in eastern Guangdong gradually weakened from the Late Triassic to the Middle Jurassic,but then gradually strengthened.The magmatic activities since the Late Jurassic in South China records late-stage subduction,and magmatism before Middle Jurassic is the induced result of the early-stage subduction of the paleo-Pacific plate.The Late Triassic volcanic rocks in South China identified in this research imply that the paleo-Pacific subduction was initiated in Late Triassic.

关 键 词：火山岩 洋壳俯冲 启动时限 晚三叠世 华南 

分 类 号：P588.14[天文地球—岩石学]