Magnesium and boron isotope evidence for the generation of arc magma through serpentinite-mélange melting  

作　　者：Xin-Yue Qiao Jia-Wei Xiong Yi-Xiang Chen Jan C.M.De Hoog Julian Pearce Fang Huang Zi-Fu Zhao Kun Chen 

机构地区：[1]State Key Laboratory of Lithospheric and Environmental Co-evolution,University of Science and Technology of China,Hefei 230026,China [2]School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China [3]Deep Space Exploration Laboratory,Hefei 230026,China [4]School of GeoSciences,Grant Institute,University of Edinburgh,Edinburgh EH93FE,UK [5]School of Earth and Ocean Sciences,Cardiff University,Cardiff CF103AT,UK

出　　处：《National Science Review》2025年第1期63-73,共11页国家科学评论(英文版)

基　　金：supported by the National Natural Science Foundation of China(42273043 and 42073029);the Fundamental Research Funds for the Central Universities.

摘　　要：Serpentinites play a crucial role in mass transport and volatile recycling in subduction zones,yet the mechanism for their contribution to the formation of arc magma remains elusive.Here,we investigate this issue by examining the magnesium(Mg)and boron(B)isotope compositions of volcanic rocks and forearc serpentinites from the South Sandwich Island arc.The volcanic rocks displayδ^(26) Mg values ranging from−0.25‰to−0.06‰andδ^(11) B values ranging from+9.6‰to+16.5‰,while the forearc serpentinites exhibitδ^(26) Mg values of−0.21‰to−0.02‰andδ^(11) B values of+5.2‰to+9.8‰.Given the substantial contrast in both Mg and B contents between mantle rocks and fluids,the combined heavy Mg-B isotope compositions of volcanic rocks pose a challenge to traditional arc formation models,i.e.flux melting of depleted subarc mantle metasomatized by slab-derived fluids.Although an alternative model involving flux melting of dehydrated serpentinites can partly account for the heavy Mg isotope compositions of arc magmas,it is difficult to simultaneously explain the B isotope and trace-element compositions.Instead,these distinct compositions can be adequately explained by partial melting of a serpentinite-dominated mélange beneath the volcanic arc.Given that arc magmas exhibiting coupled heavy Mg-B isotope compositions are increasingly reported,we propose that serpentinite-mélange melting represents an effective and geochemically self-consistent mechanism for transferring signatures of subducted slabs to the overlying mantle source.This process can be significant in subduction zones with prominent forearc mantle erosion or those involving considerable amounts of slab-hosted serpentinite.

关 键 词：arc magma Mg isotope B isotope SERPENTINITE crust-mantle interaction 

分 类 号：P597[天文地球—地球化学]