Geochemistry of subducted metabasites exhumed from the Mariana forearc:Implications for Pacific seamount subduction  

作　　者：Jianghong Deng Lipeng Zhang He Liu Haiyang Liu Renqiang Liao Abdul Shakoor Mastoi Xiaoyong Yang Weidong Sun 

机构地区：[1]Center of Deep Sea Research,Institute of Oceanology,Center for Ocean Mega-Science,Chinese Academy of Sciences,Qingdao 266071,China [2]Laboratory for Marine Mineral Resources,Qingdao National Laboratory for Marine Science and Technology,Qingdao 266237,China [3]CAS Key Laboratory of Crust-Mantle Materials and Environments,University of Science and Technology of China,Hefei 230026,China [4]University of Chinese Academy of Sciences,Beijing 100049,China [5]Centre for Pure and Applied Geology,University of Sindh,Jamshoro 76080,Pakistan

出　　处：《Geoscience Frontiers》2021年第3期358-369,共12页地学前缘（英文版）

基　　金：financially supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA22050103,XDB42020303,XDB18020102);the National Natural Science Foundation of China(Grant No.41803002);China Postdoctoral Science Foundation(No.2018 M642708);the Qingdao National Laboratory for Marine Science and Technology(2017ASKJ02);the Taishan Scholar Foundation of Shandong Province(ts201712075)。

摘　　要：Seamounts on the drifting oceanic crust are inevitably carried by plate motions and eventually accreted or subducted.However,the geochemical signatures of the subducted seamounts and the significance of seamount subduction are not well constrained.Hundreds of seamounts have subducted beneath the Philippine Sea Plate following the westward subduction of the Pacific Plate since the Eocene(~52 Ma).The subducted oceanic crust and seamount materials can be exhumed from the mantle depth to the seafloor in the Mariana forearc region by serpentinite mud volcanoes,providing exceptional opportunities to directly study the subducted oceanic crust and seamounts.The International Ocean Discovery Program(IODP)expedition 366 has recovered a few metamorphosed mafic clasts exhumed from the Mariana forearc serpentinite mud volcanoes,e.g.,the Fantangis?a and Asùt Tesoru seamounts.These mafic clasts have tholeiitic to alkaline affinities with distinct trace elements and Nd-Hf isotopes characteristics,suggesting different provenances and mantle sources.The tholeiites from the Fantangisna Seamount have trace element characteristics typical of mid-ocean ridge basalt.The Pacific-type Hf-Nd isotopic compositions,combined with the greenschist metamorphism of these tholeiites further suggest that they came from the subducted Pacific oceanic crust.The alkali basalts-dolerites from the Fantangisna and Asùt Tesoru seamounts show ocean island basalt(OIB)-like geochemical characteristics.The OIB-like geochemical signatures and the low-grade metamorphism of these alkali basalts-dolerites suggest they came from subducted seamounts that originally formed in an intraplate setting on the Pacific Plate.The Pacific Plate origin of these metabasites suggests they were formed in the Early Cretaceous or earlier.Two types of OIBs have been recognized from alkali metabasites,one of which is geochemically similar to the HIMU-EMI-type OIBs from the West Pacific Seamount Province,and another is similar to the EMII-type OIBs from the Samoa Island in southern

关 键 词：IODP 366 Mariana convergent margin FOREARC Seamount subduction OIB 

分 类 号：P736[天文地球—海洋地质]