扬子陆块西北缘早新元古代俯冲增生过程的岩浆记录  

Magmatic record of early Neoproterozoic subduction-accretion in the northwestern margin of the Yangtze Block,South China

作　　者：吴鹏[1,2] 张少兵[3] 郑永飞[3] 张小菊[1] 徐争启 施泽明[1] WU Peng;ZHANG Shaobing;ZHENG Yongfei;ZHANG Xiaoju;XU Zhengqi;SHI Zeming(College of Earth Sciences,Chengdu University of Technology,Chengdu 610059,China;Key Laboratory of Earth Exploration and Information Techniques of the China Ministry of Education,Chengdu University of Technology,Chengdu 610059,China;CAS Key Laboratory of Crust-Mantle Materials and Environments,School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China)

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]成都理工大学地球勘探与信息技术教育部重点实验室,四川成都610059 [3]中国科学院壳幔物质与环境重点实验室,中国科学技术大学地球和空间科学学院,安徽合肥230026

出　　处：《沉积与特提斯地质》2024年第1期216-230,共15页Sedimentary Geology and Tethyan Geology

基　　金：国家自然科学基金项目(41973002,41772187);成都理工大学珠峰科学研究计划项目(2023ZF11413)。

摘　　要：华南早新元古代俯冲相关岩浆作用记录为揭示罗迪尼亚超大陆边缘陆块的聚合及增生过程提供了重要制约。本文聚焦华南扬子陆块西北缘出露的早新元古代岩浆作用记录,总结梳理了其年代学框架、地球化学特征以及同位素特征,查明了其源区性质和岩石学成因、并探讨了不同阶段岩浆记录所对应的构造环境。结果表明,扬子陆块西北缘约1.0~0.9 Ga岩石具有与新生岛弧岩浆类似的微量元素特征,强不相容元素的含量略低于大陆弧,并且具有亏损的Sr-Nd-Hf同位素组成和略低于地幔值的锆石δ~(18)O值,这些特征指示约1.0~0.9 Ga岩浆岩最有可能形成于洋内弧环境。相比之下,约0.9~0.83 Ga岩浆岩具有与平均上地壳类似的微量元素特征,富集强不相容元素和轻稀土元素,亏损高场强元素,并且具有富集的SrNd-Hf同位素组成,锆石δ^(18)O值与地幔值相当或略高,指示其可能形成于大陆弧环境。此外,镁铁质岩石全岩Nd和锆石Hf同位素随年龄的长期变化趋势揭示了地幔源区性质周期性地富集和亏损,这可能是由于俯冲带间歇性地前进和后撤引起的挤压–伸展构造体制的不断交替所致。本文结果为扬子陆块西北缘新元古代早期的构造演化历史和俯冲增生动力学机制提供了制约。Early Neoproterozoic subduction-related magmatism in South China provides an important constraint for revealing the amalgamation and accretion of marginal blocks in Rodinia.Herein,we focus on the early Neoproterozoic igneous rocks exposed in the northwestern margin of the Yangtze block,South China.After compiling the geochronological data,geochemical characteristics,and isotopic compositions of early Neoproterozoic igneous rocks,the nature of source,petrogenesis,and the tectonic settings were addressed.The results show that the igneous rocks with ages of about 1.0 to 0.9 Ga have trace element compositions similar to island arc basalts with highly incompatible elements slightly lower than continental arcs,depleted Sr-Nd-Hf isotope compositions and zirconδ18O values slightly lower than mantle values,suggesting a likely intra-oceanic subduction origin.By comparison,the magmatic rocks with ages of about 0.9 to 0.83 Ga have pronounced enrichment in LILEs and LREEs,significant depletion in HFSE,moderately enriched Sr-Nd-Hf isotopes and zirconδ18O values fall in or higher than mantle range,which suggests that they were most probably formed in a continental arc setting.The secular variation trends of whole-rock Nd and zircon Hf isotopes in mafic rocks reveal the periodic enrichment and depletion of mantle caused by repeatedly advancing and retreating subduction,which further triggers alternating regimes of contraction and extension tectonics.The results depict the early Neoproterozoic subduction accretion history in the northwestern margin of the Yangtze block.

关 键 词：洋内弧 活动大陆边缘弧 早新元古代 罗迪尼亚 扬子陆块 华南 

分 类 号：P534.1[天文地球—古生物学与地层学]