Olivine basalts at the Karymskii Volcanic Center: Mineralogy, petrogenesis, and magma sources

Abstract

The olivine basalts of the Karymskii Volcanic Center (KVC) can be traced during the history of the area from the Lower Pleistocene until recently (the 1996 events); they are typical low-and moderate-potassium tholeiite basalts of the geochemical island-arc type. We have investigated the compositions of phenocryst minerals represented by plagioclase, olivine, clinopyroxene, as well as solid-phase inclusions of spinel in olivine, and more rarely in anorthite. The evolutionary trends of the rock-forming minerals provide evidence of the comagmaticity of these basalts, and thus of a long-lived intermediate magma chamber in the interior of the structure. The activity of this chamber is related to periodic transport of high temperature basalt melts to the surface. The geochemistry of the basalts is controlled by their origin at the same depleted magma source close to N-MORB, by successive crystallization of the primary melt, and by restricted mixing with magma components that are crystallizing at different depths. It is hypothesized that the solid-phase inclusions of high alumina spinel (hercynite?) found in olivine (and anorthite) of the basalts in the KVC north sector are of relict origin.