| 俯冲带火山岩硼及其同位素特征：华南中生代玄武岩初步研究 |
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| 关键词:Mesozoic basalts in Southeast China subduction slab boron content |
| 基金项目:本项目受日本COE-21合作研究基金资助。 |
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| Boron and Its Isotopes in the Subduction Zone: A Preliminary Study of Mesozoic Basalts in Southeast China |
| Although not the dominant facies, basalts are quite widely distributed in southeast China, and thus have special significance in studying the tectonic evolution of this region. The dominant eruption ages of basalts are 175±5 Ma and 80~110 Ma. In this study, all basalt samples (31 samples)，divided into three groups: Group Ⅰ (13 samples) of Middle Jurassic, Group Ⅱa (4 sampies) of Cretaceous basalts from the western part of southeast China, and Group Ⅱb (14 samples) of Cretaceous basatts from the eastern part of southeast China. Samples of Group Ⅱb are rich in LILE and show evident depletion of Nb and Ta in the spider diagram of primary mantle normalized incompatible elements, which is generally thought to be related to hydrated mantle wedge by fluids from the subduction slab. In this study, the authors aim to employ boron geochemistry to trace the source of boron in basalts from southeast China and to assess the contribution of the subduction slab to the basalt generation, in particular the generation of Group Ⅱb basalts. The boron contents of basalt samples were analyzed using the isotope-dilution (ID) ICP-MS method at the State Key Laboratory for Mineral Deposits Research, Nanjing University. The results show that, compared with recent basalts, all basalts under study are relatively poor in boron, being mainly in the range of (1~5)×10-6, with only a few samples having higher abundances (up to 19.0×10-6). The boron，other element plots（e.g., B/Ce versus Ce) for Group I basalts indicate a clear OIB affinity for Middle Jurassic basalts, which possibly erupted in anintra-continental rift setting without any contributions from subducted slab related to Pacific Plate. Further analyses of B-O-Li isotopes for these basalts may provide a better clue to their origin and tectonic settings. |
| DAI Baozhang,JIANG Shaoyong,ZHAO Kuidong,GAO Jianfeng.2005.Boron and Its Isotopes in the Subduction Zone: A Preliminary Study of Mesozoic Basalts in Southeast China[J].Acta Geoscientica Sinica,26(z1):105-108. |
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