【摘要】：本文利用電子探針技術分析了南大西洋洋中脊玄武巖中斜長石的結構構造和物質組成特征,討論了該區(qū)巖漿過程在斜長石中的記錄。按粒徑大小可將研究區(qū)玄武巖中的斜長石分為斑晶、微晶和基質三類,斑晶斜長石核部平均An值為74,屬于培長石,而邊部平均An值為69,屬于拉長石,呈正環(huán)帶構造,微晶斜長石平均An值為67,與斑晶斜長石邊部成分近似,且其粒徑與斑晶斜長石邊部寬度接近,約在30μm,極可能是同一時期形成。基質斜長石平均An值為63,略小于微晶斜長石。利用馬西茲修改后的斜長石結晶溫度計算公式,估算出斑晶斜長石核部結晶溫度約為1 214℃,斑晶斜長石邊部結晶溫度約為1 085℃,微晶斜長石的結晶溫度約為1 081℃,而基質斜長石的結晶溫度約為1 056℃。由此推測,高An值(78~80)的斑晶斜長石的核部可能是形成于巖漿源區(qū)的捕擄晶。斑晶斜長石的邊部、微晶斜長石及基質斜長石的結晶溫度相近,說明三者可能近乎同時結晶;但由于它們的顆粒大小變化范圍較大,很可能分別形成于巖漿房、巖漿通道及噴出洋殼表面后等環(huán)境中。與沖繩海槽玄武巖中斜長石比較,本區(qū)斜長石平均An值跨度以及結晶溫度跨度均比沖繩海槽小,本區(qū)An值為74~63,結晶溫度為1 214~1 056℃,而沖繩海槽An值為86~47,結晶溫度為1 250~950℃。這表明相對于巖漿物理化學環(huán)境曾經(jīng)歷快速變化的弧后盆地來說,慢速洋中脊的巖漿活動的物理化學環(huán)境則相對穩(wěn)定。
[Abstract]:In this paper, the structure, structure and material composition of plagioclase in the basalt of the mid-ocean ridge of the South Atlantic Ocean are analyzed by electron probe technique, and the records of magmatic process in the plagioclase in this area are discussed. The plagioclase in basalt in the study area can be divided into three types according to its particle size. The average An value in the core of porphyry plagioclase is 74, which belongs to the feldspar, while the average An in the edge is 69, which belongs to elongated rock and positive ring structure. The average An value of microcrystalline plagioclase is 67, which is similar to the edge component of porphyry plagioclase, and its particle size is close to the width of the edge of porphyry plagioclase, about 30 渭 m, which is probably formed at the same time. The average An value of matrix plagioclase is 63, which is slightly smaller than that of microcrystalline plagioclase. Based on the modified formula of crystallization temperature of plagioclase, it is estimated that the crystallization temperature of porphyry plagioclase core is about 1 214 鈩，

本文編號：2246073