COMPOSITIONAL HETEROGENEITY AT MUTNOVSKY VOLCANO, KAMCHATKA, RUSSIA

One of the main goals of igneous petrology is to fully understand the physical and chemical processes that drive volcanic activity, from magma production to eruption. The Mutnovsky Volcano, located along the island arc volcanic system of Kamchatka, Russia, is a stratovolcano that has been active since the late Pleistocene. The volcano has had four caldera-forming events and magmatic products have varied from basalt to rhyo-dacite with the current stage being basaltic andesites. Currently, the volcano is associated with an active geothermal system, which is being used to generate 62 MegaWatts of electricity.

The compositional heterogeneity of Mutnovsky Volcano could be the result of several different processes. The first, second, and fourth eruptive events at Mutnovsky each produced both effusive and explosive eruptions with widely varying compositions while the third eruptive event produced only basalt. I have four initial working hypotheses for development of the chemical heterogeneity of the magmas. The first hypothesis is fractional crystallization and gravitational sinking of early-formed crystals through the melt, resulting in a change in melt composition. The second hypothesis calls upon the injection of fresh, compositionally distinct magma into the chamber causing magma mixing and generating a new bulk magma composition. The third hypothesis is that an initially mafic magma, basaltic to basaltic andesite, assimilates felsic country rock and/or sediments, causing a change in magma composition. A fourth hypothesis is that varying proportions of all these processes have resulted in the diversity of magmas observed at Mutnovsky.

A variety of techniques are being used to test these hypotheses, including petrography, whole rock geochemistry, melt inclusion analyses, and U/Th disequilibria. The initial analyses give major and trace element concentrations from XRF as well as the first zircon U/Th ages from SIMS.