Diffusion coronas around quartz xenocrysts in andesite and basalt from Tertiary volcanic region in northeastern Shikoku, Japan
Diffusion coronas around quartz xenocrysts in andesite and basalt from Tertiary volcanic region in northeastern Shikoku, Japan
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日本四国东北部第三纪火山区安山岩和玄武岩中石英捕晶周围的扩散日冕
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发表时间：
1975
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影响因子：
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通讯作者：
Hiroaki Sato
中科院分区：
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作者：
Hiroaki Sato
本文描述了日本四国东北部第三纪火山岩中安山岩和玄武岩中石英捕虏晶周围的日冕。日冕主要由富钙单斜辉石和玻璃组成。整个日冕玻璃的成分剖面显示出除碱金属外的主要元素的单调变化。玄武岩熔体与石英反应的初步实验表明，碱金属是逆着浓度梯度扩散的。电晕玻璃中碱富集的这一特殊特征可以用扩散模型来解释，该模型假设硅酸盐熔体中碱的非理想性。利用SiO_2-CaO-RO（RO=MgO+FeO）体系化学势图讨论了斜方辉石安山岩冠状玻璃中富钙单斜辉石的择优结晶，认为冠状玻璃中较高的（Na+K）/Al比，增加了有效CaO浓度，从而增加了μCaO/μRO，是富钙单斜辉石择优结晶的原因。
Coronas around quartz xenocrysts in andesite and basalt from Tertiary volcanics in northeastern Shikoku, Japan, have been described. The coronas are composed mainly of Ca-rich clinopyroxene and glass. Compositional profiles across the corona glass show monotonous variation of major elements except for alkalis. Preliminary experiment on the reaction between basaltic melt and quartz has shown that alkalis diffused against their concentration gradients. This particular feature of alkali enrichment in corona glass is explained by a diffusion model, in which non-ideality of alkalis in silicate melt is assumed. Preferred crystallization of Ca-rich clinopyroxene in coronas of orthopyroxene andesite is discussed using a chemical potential diagram in the system SiO2-CaO-RO (RO=MgO+FeO), and it is suggested that higher (Na+K)/Al ratio of the corona glass, which increases the effective CaO concentration and thus increases the μCaO/μRO, is responsible for the preferred crystallization of Ca-rich clinopyroxene.