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題名 | Mineralogy and Petrology of the Ophiolite from the Namu Bridge in the North Qilian Mountains, Northwest China=中國西北北祁連山納木橋地區蛇綠岩礦物學和岩石學之研究 |
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作者 | 楊宏儀; 盧玠甫; 吳漢泉; | 書刊名 | 中國地質學會會刊 |
卷期 | 40:3 1997.07[民86.07] |
頁次 | 頁499-526 |
分類號 | 358.72 |
關鍵詞 | 蛇綠岩; 推覆型; 玻安岩; 變質作用; 祁連山; 中國; Ophiolite; Nappe-type; Boninite; Metamorphism; Qilian; China; |
語文 | 英文(English) |
中文摘要 | 中國西北北祁連山納木橋地區有下古生代推覆型的蛇綠岩套出露。這個蛇綠岩套 包括排列整齊的蛇紋岩,變質輝長岩,變質輝綠岩,具枕狀熔岩外觀的陽起石岩,以及具壓 扁,拉長,順排的枕狀熔岩外觀的陽起石片岩。伴隨著這套蛇綠岩的中性至長英質岩石常被 剪切形成糜嶺岩。整個蛇綠岩套在中洋脊或洋底時曾遭受過達綠簾-角閃岩相的熱水變質作 用。綠色片岩相的區域變質作用把部份枕狀熔岩壓扁並變質成陽起石片岩。伴隨著蛇綠岩套 構造侵位時的動力變質作用產生了糜嶺岩,斷層角礫岩,及假玄武玻璃。低鐵/鎂比值,鈦, 鋯,鈷,以及重稀元素的貧乏指示陽起石岩和陽起石片岩的源岩是源自弧前盆地的玻安岩。 微量元素的地球化學特徵也意指這個蛇綠岩套和島弧環境有關。北祁連山地區在閉合之前弧 前盆地可能曾一度開展成廣闊的海洋,產生了海洋地殼和中洋脊。 |
英文摘要 | Lower Paleozoic nappe-type ophiolite is well exposed in the Namu bridge area, North Qilian Mountains, and consists of, in an orderly sequence, serpentinites, metagabbros, metadiabases, actinolitites in the form of pillows, and actinolite schists in the form of flattened, elongated, preferred-oriented pillows. The intermediate to felsic rocks accompanying this ophiolite suite were commonly sheared to form mylonites. This ophiolite suite suffered hydrothermal metamorphism at the oceanic ridge or ocean floor up to epidote-amphibolite facies. Greenschist facies dynamothermal metamorphism converted and flattened part of the pillow lavas into actinolite schists. Dynamic metamorphism accompanied the tectonic emplacement of this ophiolite suite and produced mylonites, cataclasites, and pseudotachylites. The remarkably low FeO/MgO ratios, TiO□, Zr, and Y, and depleted HREEs suggest that the protoliths of actinolitites and actinolite schists were boninites which were originated in a fore-arc environment. Trace element geochemistry also indicates an arc-related environment for this ophiolite suite. Apparently, the fore-arc basin had developed to such an extent that the oceanic crust and perhaps the mid-oceanic ridge had once been formed in this general area before the closure of the basin in the tectonic history of the North Qilian Mountains. |
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