Geology, chemostratigraphy, and petrogenesis of the Avachinskiy volcano, Kamchatka, Russia.

摘要

Avachinskiy is a typical magmatic arc volcano. The modern cone erupts mainly basaltic andesite lavas and tephras. These lavas are dominated by a crystallizing assemblage typical of basaltic andesites found elsewhere on Kamchatka and other magmatic arcs. From numerous satellite centers, Avachinskiy has erupted a wide range of lava compositions from high-MgO basalt through dacite.;Chemostratigraphic analyses of four sections indicate that the magma chamber feeding the main cone is periodically recharged with evolved basaltic magma on time periods of about 100 to 150 years. These recharge events drive magma chemistries toward mafic compositions. Chemical modeling indicates that the variations from mafic to felsic basaltic andesite are more consistent with mixing with a dacitic magma than fractional crystallization.;The crust of the Kamchatka Peninsula is the most likely source for the dacitic mixing component. The basement rocks of Kamchatka consist of Mesozoic meta-basalts, as well as Cretaceous to Paleogene volcanic and sedimentary deposits. Partial melts of metamorphosed mafic rocks have been shown to yield low-K;Chemical modeling of Avachinskiy rocks favors magma mixing of evolved basalt and crustally derived felsic melts as the dominant mechanism of differentiation. Pure mixing can produce the majority of magmas observed at Avachinskiy, and the role of fractional crystallization is infinitesimal. The models corroborate field, petrology, and mineral chemistry data, which indicate that magma mixing is a ubiquitous process at Avachinskiy. The question still remains as to whether Avachinskiy is a special case or does this process occur at other volcanic centers only to be masked by other processes.