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 plane...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.展开更多
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).
文摘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.
