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題 名 | Ultrahigh-Pressure Metamorphism: An Overview=超高壓變質作用簡介 |
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作 者 | 俞震甫; | 書刊名 | Proceedings of the National Science Council : Part A, Physical Science and Engineering |
卷 期 | 22:5 1998.09[民87.09] |
頁 次 | 頁547-562 |
分類號 | 358.6 |
關鍵詞 | 超高壓變質作用; Mineral inclusion; Tectonic exhumation; Ultrahigh-pressure metamorphism; |
語 文 | 英文(English) |
中文摘要 | 超高壓變質作用是指變質時壓力條件超過石英-柯石英平衡界線之變質作用。目 前在世界上含有微鑽石及柯石英包�媗擗圻a殼源超高壓岩石出露於五個大陸碰撞造山帶中, 證實了地殼岩石可因大陸碰撞而隱沒至超過一百公里的地函深度。實驗礦物/岩石學亦確立 了與超高壓變質條件特別相關的一些礦物(群)。這些礦物(群)能保存於地表的溫壓條件, 主要肇因於超高壓岩體的快速上升,以及上升時環境缺乏液相和持續的冷凍效應。由於在某 些造山帶中,超高壓礦物(群)發現的地點相當侷限,因此實不易據以界定超高壓岩體的區 域規模。此外,目前的資料亦顯示超高壓變質作用發生時,環境中水的活性應相當低,且變 質液相中亦含有相當量的氬氣,造成超高壓礦物在形成時均含“超氬”而不利於氬氣定年。 根據定年工作及變質溫壓的估計,超高壓變質岩體由地函深度上升至下地殼深度的速度應大 於7-14釐米/年;唯因缺乏一些關鍵性的控制條件,對超高壓岩體上升的地體構造機制模式, 目前尚無定論。 |
英文摘要 | The ultrahigh-pressure (UHP) metamorphism wa defined as the metamorphism occurring under pressure conditions higher than the quartz-coesite equilibrium curve. Based on the discovery of microdiamond and coesite inclusions, UHP metamorphic rocks of crustal origin have been reported from five continent-collision orogenic belts around the world. This shows that crustal rocks can be subducted to mantle depths (>100 km) during continetal collision. Several minerals/mineral assemblages characteristically relevant to UHP conditions have also been established through experimental studies. A fast exhumation rate, the absence of a fluid phase and the continuous refrigeration effect during exhumation are required to preserve UHP minerals at the Earth's surface. However, the restricted occurrence of UHP minerals makes it difficult to confidently establish a regional scale for some UHP terranes. It was demonstrated that water activity in fluid phase during UHP metamorphism was low. "Excess Ar" was also shown to be commonly incorporated within UHP minerals, causing difficulties in Ar geochronology. Age dating of UHP rocks combined with petrologic pressure-temperature studies revealed that the exhumation rate of UHP rocks from mantle depths to the lower crustal level was higher than 7-14 mm/yr. The geodynamic model for the exhumation mechanism(s) of these UHP terranes, however, remains controversial due to the lack of key constraints. |
本系統中英文摘要資訊取自各篇刊載內容。