Genetic Environments of High-magnesian andesite and Related Rocks.

对四国东北部、诺东半岛和九州西北部的高镁安山岩和小笠原群岛的博长岩进行了地质、岩石学和化学研究。四国东北部的高镁安山岩（sanukitoid）可能是水合地幔橄榄岩的原生安山岩，但其源区可能受到俯冲沉积的严重影响。诺托半岛和西北九州的青铜安山岩可能是由原始玄武岩与英安岩或流纹岩岩浆混合形成的。小笠原群岛boninite微量元素组成具有低HFSE和较高碱含量的特点，含中间碱土。这种富集（如高Rb/Ba和Ba/La比值）在目前研究的高镁质安山岩中很常见，可以从岛弧拉斑岩中诊断出来。对一些火山岩的大气熔融研究提供了一种新的氧逸度计。利用斜长石与岩浆之间的镁铁配分关系。氧逸度计在ca. log _2=-6 - -11范围内灵敏度较高，对斜长石-植生火山具有广泛的适用性。

Gelogical, petrographical and chemical studies were carried out on high-magnesian andesites of northeast Shikoku, Noto Peninsula, and northwest Kyushu, and boninite of Ogasawara Islands. High-magnesian andesite (sanukitoid) of northeast Shikoku may repesent primary andesite derived from hydrated mantle peridotite, though the source area may be aeverely affected by subducted sediments. Bronzite andesites of Noto Peninsula and NW Kyushu were probably formed by mixing of primitive basalt and dacite or rhyolite magmas. Trace element composition of boninite of Ogasawara Islands is characterized by low HFSE and rather high alkali contents with intermediate alkali earths. Such enrichement (e.g. high Rb/Ba and Ba/La ratios) is common among the high-magnesian andesites presently investigated, and is diagnostic from island arc tholeiites.1-atmosphere melting studies of some volcanic rocks afforded a new oxygen fugacity meter. It uses Mg-Fe partition relationship between plagioclase and magma. The oxygen fugacity meter is sensitive at ca. log fo_2=-6 - -11, and may have wide applicability to plagioclase-phyric volcanics.