| “三江”古特提斯地幔热柱——洋中脊玄武岩证据 |
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| 引用本文：侯增谦,莫宣学,朱勤文,沈上越.1996.“三江”古特提斯地幔热柱——洋中脊玄武岩证据[J].地球学报,17(4):362-375. |
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| 中文摘要:本文通过研究三江地区金沙江和澜沧江缝合带ＭＯＲＢｓ的时空分布配置、岩石组合类型、岩石地球化学及区域地化异常，揭示了地幔热柱对古特提斯岩石圈内ＭＯＲＢｓ源岩及ＭＯＲＢｓ的化学成分影响，讨论了地幔热柱对古特提斯洋开启的驱动机制及对岩石圈演化的制约作用。ＭＯＲＢ沿金沙江和澜沧江洋脊与ＯＩＢ分段产出，但在过渡地段，ＭＯＲＢ与ＯＩＢ交互产出，密切共生，并沿洋脊展示明显的地球化学异常。ＭＯＲＢ有３种类型，其中，富集型ＭＯＲＢ靠近ＯＩＢ分布区产出，相对富集ＬＲＥＥ、ＨＦＳＥ和ＬＩＬＥ，显示Ｅ－ＭＯＲＢ地化特征。亏损型ＭＯＲＢ远离ＯＩＢ分布区产出，相对亏损不相容元素，显示Ｎ－ＭＯＲＢ地化特征。过渡型ＭＯＲＢ在ＭＯＲＢ与ＯＩＢ过渡地段产出，则显示Ｔ－ＭＯＲＢ地化特征。ＭＯＲＢ地化特征和空间分布揭示，洋脊具有明显的块段特点，ＯＩＢ区洋脊具热幔柱洋脊特点，亏损型ＭＯＲＢ区洋脊具正常洋脊特征，而过渡型ＭＯＲＢ区段则具过渡型洋脊特征。混合模式计算表明，富集型和过渡性ＭＯＲＢｓ系亏损型ＭＯＲＢ端元与ＯＩＢ端元不同程度的混合产物，揭示地幔热柱物质与其周围的亏损地幔（Ｎ－ＭＯＲＢ源岩）发生了大规模物质能量交换。 |
| 中文关键词:三江特提斯 洋脊玄武岩 地幔热柱 |
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| Mantle Plume in the Sanjiang Paleo-Tethyan Lithosphere:Evidence from Mid-Ocean Ridge Basalts |
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| Abstract: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. |
| keywords:Sanjiang Tethys mid-Ocean ridge basalts mantle plume |
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