Deep recycling of volatile elements in the mantle:Evidence from the heterogeneous B isotope in intra-plate basalts  

作　　者：Yan-Qing Li Hiroshi Kitagawa Chang-Qian Ma Eizo Nakamura Chie Sakaguchi Katsura Kobayashi Xiang-Yun Hu 

机构地区：[1]School of Geosciences,Yangtze University,Wuhan 430100,China [2]International Center for Isotope Effects Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China [3]Pheasant Memorial Laboratory,Institute for Planetary Materials,Okayama University at Misasa,682-0193 Misasa,Tottori,Japan [4]Schoole of Earth Sciences,China University of Geosciences,Wuhan 430074,China [5]Institute of Geophysics&Geomatics,China University of Geosciences,Wuhan 430074,China

出　　处：《Geoscience Frontiers》2024年第6期303-320,共18页地学前缘（英文版）

基　　金：supported by the National Natural Science Foundation of China(Grant Nos.42173015 and 41702057);China Postdoctoral Science Foundation(2017M612530);the MEXT(Ministry of Education,Culture,Sports,Science and Technology).

摘　　要：Volatiles in the mantle are crucial for Earth’s geodynamic and geochemical evolution.Understanding the deep recycling of volatiles is key for grasping mantle chemical heterogeneity,plate tectonics,and long-term planetary evolution.While subduction transfers abundant volatile elements from the Earth’s surface into the mantle,the fate of hydrous portions within subducted slabs during intensive dehydration processes remains uncertain.Boron isotopes,only efficiently fractionating near the Earth’s surface,are valuable for tracing volatile recycling signals.In this study,we document a notably large variation inδ^(11)B values(−14.3‰to+8.2‰)in Cenozoic basalts from the South China Block.These basalts,associated with a high-velocity zone beneath East China,are suggested to originate from the mantle transition zone.While the majority exhibitδ^(11)B values(−10‰to−5‰)resembling the normal mantle,their enriched Sr-Nd-Pb isotope compositions and fluid-mobile elements imply hydrous components in their source,including altered oceanic crust and sediments.The normalδ^(11)B values are attributed to the dehydration processes.Remarkably highδ^(11)B values in the basalts indicate the presence of subducted serpentinites in their mantle source.A small subset of samples with lowδ^(11)B values and radiogenic isotope enrichments suggests a contribution from recycled detrital sediments,though retaining minimal volatile elements after extensive dehydration.These findings provide compelling evidence that serpentinites within subducted slabs predominantly maintain their hydrous nature during dehydration processes in subduction zones.They may transport a considerable amount of water into deep mantle reservoirs,such as the mantle transition zone.

关 键 词：Intra-plate basalts Boron isotopes SERPENTINITE Volatile recycling Mantle heterogeneity 

分 类 号：P542.5[天文地球—构造地质学] P597[天文地球—地质学] P588.14