研究生: |
林治蔚 Lin Chih-Wei |
---|---|
論文名稱: |
海洋鑽探計劃187航次玄武岩之實驗岩石學研究 |
指導教授: | 劉德慶 |
學位類別: |
碩士 Master |
系所名稱: |
地球科學系 Department of Earth Sciences |
論文出版年: | 2002 |
畢業學年度: | 90 |
語文別: | 中文 |
論文頁數: | 69 |
中文關鍵詞: | 海洋鑽探計劃 、中洋脊玄武岩 、實驗岩石學 |
英文關鍵詞: | AAD |
論文種類: | 學術論文 |
相關次數: | 點閱:256 下載:9 |
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摘 要
本研究所使用的岩石樣本,為海洋鑽探計劃第187航次於東南印度洋脊附近所鑽獲的海洋地殼玄武岩,其主要組成礦物為斜長石及橄欖石,結晶顆粒小,無斑狀組織,屬無斑隱晶質玄武岩。
本研究的目的在模擬自然界岩漿所在的環境,來了解此玄武岩質岩漿在不同壓力下的結晶溫度及結晶次序,更進一步探討其岩漿演化的機制及過程,推論此岩石的生成環境。
根據實驗結果,其一大氣壓下的全熔溫度約為1269℃,固相線溫度稍低於1169℃。結晶次序為:氧化物、斜長石、斜輝石及橄欖石、直輝石(橄欖石消失)。斜長石的An值,隨溫度的下降有降低的趨勢;各溫度晶出之斜輝石成分則變化不大;氧化物則隨溫度下降鐵、鈦的含量上升,鉻、鎂則下降。1.0京帕下的全熔溫度約為1280℃,固相線溫度低於1160℃。結晶次序為:斜長石及斜輝石、直輝石、鈦鐵氧化物。
在玄武岩四面體的分類中,原岩屬橄欖石矽質玄武岩,殘餘岩漿有向石英矽質玄武岩演化的趨勢。一大氣壓下,隨著溫度下降玻璃成分之矽含量上升;鋁、鈣及鎂則下降;Na2O/TiO2與MgO值,皆隨溫度下降而降低,以此而言,太平洋型中洋脊玄武岩,並不會經過結晶分化而演變成印度洋型。在AFM圖中,岩漿初始成分在矽質玄武岩範圍內,演化初期朝全量鐵富集,之後向鹼金屬富集。
根據實驗結果,殘餘岩漿成分有朝向石英富集的趨勢,一大氣壓及1.0京帕下礦物晶出的順序和前人研究相符。和原岩中的礦物相比較後,顯示此玄武岩應該是在1.0京帕及一大氣壓之間,較接近一大氣壓的低壓環境下生成,生成深度小於30公里。
本研究之中洋脊玄武岩形成過程為,在上升的過程中經過些微結晶分化,隨著岩漿的上升、溫度的下降,在橄欖石晶出之後,因接近海床面而急速冷卻,所以形成主要礦物為斜長石及橄欖石的玄武岩。
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