Composition of melts and minerals from volcanic rocks of the Kuril-Kamchatka Arc

In this paper allivalites, coarse- and giant-textured olivine-anorthite rocks occurring as separate blocks in the eruption products of many volcanoes from the frontal part of the Kuril-Kamchatka Arc are under consideration. New data are reported on petrography, mineralogy, and composition of melt inclusions in minerals from ten allivalite samples collected at Ksudach, Ilinsky, Zavaritsky, Kudryavy, and Golovnin Volcanoes. Crystallization temperatures of allivalite minerals were estimated as 970-1080°C at melt water content of 3.0-3.5 wt % and oxygen fugacity NNO=1-2. Genetic connection was established between compositions of melt inclusions and interstitial glasses in allivalites and volcanic rocks. Cumulate nature of allivalites was demonstrated. Using mass balance calculations, degree of fractionation of primary melts during formation of cumulate layers was estimated for various volcanoes as 22-46%.

本文聚焦产于千岛-堪察加弧（Kuril-Kamchatka Arc）前缘诸多火山喷发产物中、以孤立岩块形式产出的橄长岩（allivalite）——即具粗粒与巨粒结构的橄榄石-钙长石岩石。本次研究报道了采自克苏达奇（Ksudach）、伊林斯基（Ilinsky）、扎瓦里茨基（Zavaritsky）、库德里亚维（Kudryavy）与戈洛夫宁（Golovnin）火山的10个橄长岩样品中，矿物的岩石学特征、矿物学组成及矿物内熔体包裹体成分的全新数据。研究估算得到，该类橄长岩矿物的结晶温度介于970~1080℃，对应熔体水含量为3.0~3.5 wt%，氧逸度为NNO=1~2。本研究确立了橄长岩内熔体包裹体、填隙玻璃的成分，与火山岩成分之间的成因关联。研究证实了橄长岩的堆晶成因。通过质量平衡计算，本研究估算得到不同火山的堆晶岩层形成过程中，原始熔体的分异程度为22%~46%。