| “三江”古特提斯地幔热柱——洋中脊玄武岩证据 |
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| 关键词:Sanjiang Tethys mid-Ocean ridge basalts mantle plume |
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| Mantle Plume in the Sanjiang Paleo-Tethyan Lithosphere:Evidence from Mid-Ocean Ridge Basalts |
| Basalts from several sections of the Lancangiiang and Jinshajiang suture zones close to mantle plumes supposed by Hou et al (1996) have been investigated to understand the influence of the mantle plume on the geochemistry of MORBs and on the evolution of the Paleo-Tethyan lithosphere in Sanjiang, China. Ophiolite mapping and petrographical observation show that MORBs interbed with OIBs in 220-240N in the Lancangjiang suture zone and in 240-270N in the Jinshajiang suture zone, and occurred as member of ophiolite and opholitic melange far from OIB region. Although the basalts petrographically show only limited variation, three basaltic types were distinguished based on their major elements, LILE, HFSE and REE compositions. One group displays geochemical characteristics enriched in incompatible and LREE elements, and can be characterized as E-type mid-ocean ridge basalts. The second group shows depletion in incompatible and LREE elements, and is similar to N-type MORBs, whereas third group exhibits transitional geochemical characteristics, and can be referred to as T-type MORBs. On a broad scale, there are clear geochemical "anomaly" occurring in 220-240N in the Lancangjiang suture zone and in 240-270N in the Jinshajiang suture zone. These geochemical enrichment anomalies corresPOnd to mantle plumes occurring underneath both two branches of the Sanjiang Paleo-Tethy Ocean, respectively.Mixing hyperbolae for the incompatible element and ratios suggest that extensive mixing of an end-member charactered by a plume matter with an end-member of normal depleted MORB, can explain the occurrence of the three type basalts in the Paleo-Tethys. Based on the tectono-magmatic events, spatial distribution of MORB-OIB association, geochemical characteristics of MORBs and geochemical anomaly in the Sanjiang Tethyan Region, a geoclynamic model for evolution of the Paleo-Tethys lithosphere is suggested. The model emphases that the Paleo-Tethys experiences two evoluted stages, i. e., plume-controlled Atlantic stage and plate-controlled Pacific stage. The plume from deeper mantle probably took Pace mass and energy exchanges with surrounding mantle and supplies a huge driving force to result in thinning of lithosphere and opening of oceanic basins in the Paleo-Tethys Ocean in Devonian-carboniferous period. |
| HOU Zeng-qian,MO Xuan-xue,ZHU Qin-wen,SHEN Shang-yue.1996.Mantle Plume in the Sanjiang Paleo-Tethyan Lithosphere:Evidence from Mid-Ocean Ridge Basalts[J].Acta Geoscientica Sinica,17(4):362-375. |
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