PETROLOGICAL-GEOCHEMICAL MODEL FOR GENETIC-RELATIONSHIPS BETWEEN BASALTIC AND ANDESITIC MAGMATISM OF KLYUCHEVSKOI AND BEZYMYANNYI VOLCANOS,KAMCHATKA

The paper reports data on the deep structure and feeding system of Kly uchevskoi and Bezymyannyi volcanoes, distinctive features of their eru ptive activity, and nevi geochemical data on their basalts and andesit es. The materials are used to discuss the concept of a common deep-sea ted source af the vulcanoes. The fractionation products of the source underwent a complex evolution during their ascent along the system of volcanic conduits. The magmas of the Klyuchevskoi and Bezymyannyi volc anoes are thought to have originated in notably different geodynamic a nd thermodynamic environments and, thus, yielded two ''reduced'' volca nic series: the predominantly basaltic series of Klyuchevskoi volcano and the basaltic andesite-dacite series of Bezymyannyi volcano, Both o f the series experienced crystal fractionation with a subordinate role of other petrogenetic processes. According to the concept, the two vo lcanic series compose a single evolutionary series (a specific geochem ical system), whose source was upper mantle peridotitic material and w hose derivatives encompass a broad spectrum of volcanics ranging from mafic to acid rocks.