摘要
火山是岩浆活动在地表的主要呈现形式,古老火山由于剥蚀作用出露多阶段火山喷发产物及岩浆通道、岩浆房等,从而为揭示岩浆房内部结构和成分演化提供重要窗口。锆石在长期结晶生长过程中,能够记录岩浆系统的结晶分异、晶体-熔体分离和岩浆补给等过程。闽西南晚侏罗世廖天山破火山是保存最完整的中国东南部晚中生代早期代表性破火山之一,本文对其开展锆石U-Pb年代学、Lu-Hf同位素组成和微量元素成分分析,以期揭示其火山活动时序、岩浆来源和演化过程。廖天山火山活动具有阶段性和多期次性,一段火山活动开始于约161.5±0.7 Ma,喷发断续且规模较为有限;二段火山岩形成于159.9±0.9~156.9±0.8 Ma,该时段喷发产物规模巨大,构成破火山主体;最后岩浆在153.2±0.7 Ma沿火山通道侵出形成流纹斑岩岩穹,标志着火山活动的结束。锆石Lu-Hf同位素组成显示,廖天山破火山岩浆主要源于古元古代地壳基底的部分重熔,但有不同程度的亏损幔源物质贡献,且在三个火山活动阶段中幔源物质参与比例不同,二段火山岩中相对较低。不同批次岩浆可能从源区分别上升,在深部岩浆房发生岩浆混合,而后在浅部岩浆房短暂留存发生分离结晶作用。根据岩浆来源的变化和火山岩相组合,我们认为廖天山火山活动形成于相对挤压转向伸展的构造环境,受制于晚侏罗世古太平洋板块俯冲以及板片俯冲角度变化的地球动力学背景。
Volcanoes are the only straightforward expression for the activity of magma on Earth\s surface.Ancient volcanoes could expose multi-stage eruptive products,magma plumbing systems and even the magma reservoirs.Therefore,they could preserve important information on interior structure of magma reservoir and magmatic evolution.Zircons can record crystallization differentiation,crystal-melt separation,and replenishment processes of magma system.In this work,we conducted zircon U-Pb,Lu-Hf isotopic and trace element concentration studies on the late Jurassic Liaotianshan caldera in southwest Fujian Province,which is one of the earliest and best preserved Late Mesozoic calderas in SE China,to reveal its eruptive history,magma source and evolution process.The Liaotianshan volcano started to erupt intermittently at ca.161.5±0.7 Ma as the first stage with limited scales of eruptive products,then during 159.9±0.9~156.9±0.8 Ma erupted as the second stage forming the main part of the caldera.At the final stage,magma extruded along the magma conduit forming porphyritic rhyolite domes at ca.153.2±0.7 Ma,marking the end of the eruption.Zircon Lu-Hf isotopic compositions show that,the Liaotianshan volcanic rocks were derived mainly from partial remelting of the Paleoproterozoic crustal basement,with decreasing and then increasing degree of depleted mantle-derived involvement.Different batches of magma raised separately from source region after magma mixing in deep reservoir,and then retained briefly in shallow reservoir with similar crystallization process.The change of magma origin together with volcanic lithofacies indicate that the Liaotianshan caldera formed under a slightly compressional and then depressional geological environment,plausibly corresponding to the paleo-Pacific subduction with varying subduction angle during Late Jurassic.
作者
刘磊
赵阳
贺振宇
孙杰
刘希军
赵增霞
LIU Lei;ZHAO Yang;HE Zhenyu;SUN Jie;LIU Xijun;ZHAO Zengxia(Guangxi Key Laboratory of Hidden Metallic Ore Deposits Erploration,Collaborative Innovation Center for Erploration of Nonferrous Metal Deposits and Efficient Utilization of Resources,Guilin University of Technology,Guilin,Guangzi 541004,China;School of Civil and Resource Engineering,University of Science and Technology Beijing,Beijing 100083,China)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2023年第7期2176-2194,共19页
Acta Geologica Sinica
基金
国家自然科学基金项目(编号42073031,41702056)
广西科技计划项目(编号2021GXNSFAA220077,2021GXNSFBA220063)联合资助的成果。
