| “三江”义敦岛弧带玄武岩喷发序列与裂谷—岛弧转化 |
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| 引用本文：侯增谦,莫宣学,谭劲,胡世华,罗再文.1993.“三江”义敦岛弧带玄武岩喷发序列与裂谷—岛弧转化[J].地球学报,14(1):49-67. |
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| 中文摘要:岩石-构造组合是恢复古板块构造历史的最有效手段之一,同时是表征古板块边界与板内环境的最重要的地质证据。本文拟从岩石-构造组合角度,通过对义敦岛弧带玄武岩,特别是前岛弧期玄武岩喷发序列、岩石组合、地球化学特征和其形成背景的研究,试图从较深层次上揭示岩浆-构造内在联系,探索义敦古岛弧的形成与发展。 |
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| THE ERUPTION SEQUENCES OF BASALTS IN THE YIDUN ISLAND-ARC, SANJIANG REGION AND EVOLUTION OF RIFT TO ISLAND-ARC |
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| Abstract:There were two of cycles of basaltic volcanism in the early stage of formation of the Yidum Island-Arc: Genlong cycle and Gacun(Xiacun)cycle. The Genlong cycle may be divided into three subcycles: Nalenghai, Genlong and Chizhong subcycles. The rock suites in the Nalenghai subcycle include a basalt-rhyolite bimodal suite and basaltic rocks, which constitute an alkaline basaltic magma series. The basalts are geochemically characteristic of continent rift basalt. The center of volcanism in the Genlong subcycle moved from both sides to the central part, with the rock series changing from the alkaline series to the tholeiitic one.Petrological and geochemical studies show that the basaltic rocks are geochemically transional and have a trendency of evolution of rift basalts to seafloor basalts. The rocks of the Chizhong subcycle consists of pillowmassive tholeiitic basalts and boninites.The pillow basalts, formed in the early stage of basaltic volcanism, are transitional whereas the massive basalts in the later stage are more familiarized with typical island-arc tholeiitic basalts. The volcanic rocks of the Gacun cycle consist of basalt-andesite-dacite, which belong to the calc-alkaline series. The rocks are typical island-arc volcanics.A petrological model on the early-stage evolution of the Yidun Island-Arc is suggested on the base of studies on rock association, temporal-spacial distribution, petrology and geochemostry of basalt sequences. The evolution history is divided into three stages; 1) fromation of a horse-graben system of rift on continental margin; 2) evolution of the rift to an island-arc through back-arc opening; 3) intense arc-forming volcanism. |
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