• 作者： 黃武良
• 作者服務機構： 國立臺灣大學地質學系
• 中文摘要： 玄武岩及安山岩中之鎂/鐵及鈉/鉀在各礦物及液體間於十五仟粑下之分配關係，以電子微探針分析之。實驗之結果如下：(1)玄武岩之近全溶礦物為柘榴子石和斜輝石及少量之角閃石，而安山岩中則為柘榴子石和角閃石及少量之斜輝石。(2)柘榴子石之鎂/鎂+鐵的比值是在所有共存礦物中唯一比原來之玄武岩及安山岩為低者;柘榴子石之分化結晶是導致殘留液中含鐵量不增加的主要作用。(3)斜輝石之鎂/鎂+鐵之平均比值在玄武岩中為0.70，在安山岩中為0.63，此仍為共存礦物中最高者；斜輝石之分化結晶作用，將使液體中之含鐵量增加，不過將立即為同時結晶出之柘榴子石所抑制。(4)鎂/鎂+鐵在角閃石中之比值皆拘限在很小的範圍，從0.56到0.60，這個值很近似於玄武岩之比值，但比安山岩之比值大得很多;因此，角閃石之分化結晶，只有從玄武岩漿中才可產生液體含鐵量不增加的現象，從安山岩漿中無法辦到；一種基性岩槳經由角閃石之分化結晶，只有在早期可獲得類似鈣鹼性趨勢之岩漿，到了中期，中性岩漿之含鐵量有增加之趨勢。(5)殘留液之鈉/鉀的比值，在玄武岩中主要受角閃石及斜輝石之分化結晶的控制，而在安山岩中受角閃石及斜長石；由((4)之討論得知角閃石之分化結晶不可能是，使安山岩漿分化類似於鈣鹼性趨勢的主要作用，故在鈣鹼性岩漿中鈉/鉀比值之減少，主要是斜長石分化結晶所致，。
• 英文摘要： The distribution of Mg/Fe and Na/K ratios among coexisting crystals and glass in basalt and andesite starting compositions with 5 wt.% H2O was experimentally determined at 15 kb. Results include the following: (1) Garnet and clinopyroxene with subordinate amphibole are near-liquidus phases in basalt while garnet and amphibole with subordinate clinopyroxene are those in andesite. (2) Garnet is the only crystalline phase that has Mg/Mg+Fe ratio lower than the starting basalt and andesite; garnet fractionation is the dominant process to yield residual liquid lacking of iron enrichment in both basalt and andesite. (3) Clinopyroxene possesses the highest Mg/Mg+Fe ratio with average 0.70 in andesite; fractionation of clinopyroxene yields liquid rich in iron which is counterpoised by simultaneous crystallization of garnet. (4) Amphibole has Mg/Mg+Fe in a small range from 0.56 to 0.60 which is similar to the ratio in basalt but much higher than the ratio in andesite, therefore, amphibole fractionation may produce liquids lacking of iron enrichment from basaltic magma but not from andesitic magma; differentiation of a basic magma by ambhibole fractionation may yield liquid with Mg/Fe similar to calc-alkaline trend only in early stage but not in the intermediate stage. (5) Na/K ratio in succesive liquid is controlled by fractionation of amphibole and clinopyroxene in basalt and by fractionation of amphibole and plagioclase in andesite. Since amphibole can not be the major cumulate in andesitic magmas to yield residual liquids similar to calc-alkaline trend as discussed in (4), the Na/K ratio of residual liquid is mainly controlled by fractionation of plagioclase, causing a significant decrease in the ratio.
• 中文關鍵字： --
• 英文關鍵字： --