GEOTHERMOMETRY OF MUTNOVSKY VOLCANO, RUSSIA, AND IMPLICATIONS FOR MAGMATIC EVOLUTION

Mutnovsky Volcano, located on the southern portion of the Kamchatkan island arc chain, has been active since the late Pleistocene. It is postured to be the driving heat source for a hydrothermal system that is being tapped by a geothermal energy plant, powering one third of the peninsula.

Mutnovsky is a volcanic complex of four stratocones formed as the magma plumbing system shifted position over time. Mutnovsky I-III have a range of compositions from basalt to rhyodacite while Mutnovsky IV is all basalts and basaltic andesites. Samples from all four centers were collected and analyzed for major and trace element chemistry. Electron microprobe analyses of clinopyroxene, orthopyroxene, and olivine have been used to obtain temperatures of crystallization. Two methods were used to calculate two-pyroxene temperatures, the QUILF (Lindsley and Anderson, 1983) method and the Brey and Kohler (1990) method. Calculated temperatures were very similar between the two methods, but only Brey and Kohler temperatures are reported here, with 2 sigma uncertainties. Average temperatures for Mutnovsky I are 1016 +/- 111 C for basalts, 960 +/- 86 C for basaltic andesites, 948 +/- 73 C for andesites, and 938 +/-96 C for dacites. For Mutnovsky II, basalts have an average temperature of 1030 +/- 90 C, basaltic andesites are 1048 +/- 73 C, and andesites and dacites weren’t found with co-existing ortho- and clinopyroxene. Average temperatures for Mutnovsky III are 1021 +/- 89 C for basalts, 866 +/- 32 C for andesites, and 878 +/- 65 C for dacites. Mutnovsky IV has an average basalt temperature of 989 +/- 98 C; no basaltic andesites had co-existing pyroxenes.

Crystallization temperatures provide insight into the conditions in the magma chamber that resulted in the compositional heterogeneity we see at the surface. Tracking the temperature of each composition, within each center, will point out any temperature anomalies that could represent injections of fresh, hot magma. These injections are potentially the cause of magma mixing, for which there is evidence both in observed field textures and in normal and reverse plagioclase zoning.