Ueno basaltic rocks I
Ueno basaltic rocks I
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上野玄武岩 I
DOI：
10.2465/ganko.88.272
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发表时间：
1993
期刊：
影响因子：
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通讯作者：
S. Nakano
中科院分区：
文献类型：
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作者：
S. Nakano
坂下和铃兰是日本中部岐阜县上野玄武岩中最大的两个单成因火山，其时代为上新世至更新世。测定了这两座火山熔岩的体积组成和矿物组成。它们在岩相学和化学上表现出显著的不均匀性。它们由（普通辉石-）橄榄玄武岩到玄武安山岩组成，SiO2含量分别为50.3- 55.2wt%和48.4- 53.9wt%。它们的成分在变异图中构成了近乎直线的趋势线。橄榄石的铁镁分带类型有三种。A型的特征是一个几乎均匀的宽核（Fo 82 -88）和一个高度分带的窄边。C类从核心到边缘（Fo 64 -77）未分区。类型B通常是分区的，是介于A和C之间的中间类型。橄榄石斑晶与A型分区的核心组成被解释为不受晶体-熔体扩散。C型分带是由于扩散作用使所有分带消失的结果。斑晶矿物的化学成分表明，橄榄石首先在稳定的岩浆环境中开始结晶，而普通辉石和斜长石斑晶的成核和生长温度比橄榄石晚。利用主量元素混合计算结果表明，岩石化学异质性是由橄榄石、普通辉石、斜长石和钛磁铁矿的分离结晶作用引起的，同时伴随着大量低钾酸性岩石的同化作用。然而，根据微量元素化学，要求同化物具有富集Th、Sr、Ba、Zr、Nb等的特殊化学成分，但与分布在上野玄武岩附近的正常酸性岩石相比，K和Rb高度亏损。
Sakashita and Suzuran are two largest monogenetic volcanoes belonging to the Ueno basaltic rocks of Pliocene to Pleistocene age in Gifu Prefecture, central Japan. Bulk and mineral composi-tions of lavas from these two volcanoes are determined. They show petrographically and chemically remarkable heterogeneities. They are composed of (augite-) olivine basalt to basaltic andesite with 50.3-55.2 and 48.4-53.9 wt% SiO2, respectively. Their compositions construct nearly straight trend lines in variation diagrams. Three Fe-Mg zoning types of olivine are recognized. Type A is characterized by a nearly homogeneous broad core (Fo82-88) and a highly-zoned narrow rim. Type C is unzoned from core to rim (Fo64-77). Type B is normally zoned, an intermediate type between A and C. Core compositions of olivine phenocrysts with type A zoning are interpreted to be not affected by crystal-melt diffusion. Those with type C zoning result from obliteration of all zoning by diffusion. Chemical compositions of phenocrystic minerals indicate that olivine began to crystal-lize first in a stable magmatic environment, while existing phenocrysts of augite and plagioclase nucleated and grew later at lower temperatures than olivine. Mixing calculations using the major-element compositions reveal that the chemical heter-ogeneities are caused by fractional crystallization of olivine, augite, plagioclase and Ti-magnetite, with a significant amount of accompanying assimilation of low-potassium acidic rocks. Based on the trace-element chemistry, however, the assimilant is requested to have peculiar chemical compositions enriched in Th, Sr, Ba, Zr, Nb etc., but highly depleted in K and Rb compared with normal acidic rocks distributed in the vicinity of the Ueno basaltic rocks.
福冈高明：（1987）
DOI：
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发表时间：
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影响因子：
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