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

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外文摘要：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 pro-cesses remains uncertain.Boron isotopes,only efficiently fractionating near the Earth's surface,are valu-able for tracing volatile recycling signals.In this study,we document a notably large variation in δ11B 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 exhibit δ11B 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 normal δ11B values are attributed to the dehydration processes.Remarkably high δ11B values in the basalts indicate the presence of subducted serpentinites in their mantle source.A small subset of samples with low δ11B 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 sub-ducted 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 man-tle transition zone.

外文关键词：

Intra-plate basaltsBoron isotopesSerpentiniteVolatile recyclingMantle heterogeneity

作者：

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

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作者单位：

School of Geosciences,Yangtze University,Wuhan 430100,China

International Center for Isotope Effects Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China

Pheasant Memorial Laboratory,Institute for Planetary Materials,Okayama University at Misasa,682-0193 Misasa,Tottori,Japan

Schoole of Earth Sciences,China University of Geosciences,Wuhan 430074,China

Institute of Geophysics & Geomatics,China University of Geosciences,Wuhan 430074,China

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出版年：

2024

DOI：

10.1016/j.gsf.2024.101900

地学前缘(英文版)

中国地质大学（北京）北京大学

地学前缘(英文版)

CSTPCD

影响因子：0.576

ISSN：1674-9871

年,卷(期)：2024.15(6)