CONNECTIONS BETWEEN ERUPTION STYLE AND MAGMATIC RESERVOIR EVOLUTION: INSIGHTS FROM AUGUSTINE VOLCANO, ALASKA, USA
Here we are initiating a detailed study of the Tephra M deposits using a combination of major element bulk rock and glass compositions, plagioclase hygrometry, and Fe-Ti oxide (ilmenite-magnetite) thermometry. Preliminary Fe-Ti oxide thermometry suggest that the Tephra M magma ranged in temperature from approx. 870 to 980°C. These results overlap with published 860 to 1120°C Fe-Ti oxide temperatures from the 2006 eruption, but maximum temperatures reported for 2006 are notably higher than any we have found to date in Tephra M components. In addition, studies of the 2006 eruption have found evidence for the intrusion of hotter, mafic magma (56 – 59 weight % SiO2) into stored cooler, felsic magma (62 – 63 weight % SiO2) prior to the eruption. Available analysis of Tephra M pumice (62 – 64 weight % SiO2; n = 5) are compositionally similar to the 2006 felsic endmember magma. Current efforts will explore if this maximum temperature difference is legitimate, and if the difference influenced the explosivity of Tephra M compared to 2006 eruption. We are studying components identified at 7 sample localities collected for Tephra M to better document potential compositional differences between the eruptions, along with plagioclase analyses to constrain volatile concentrations that may have affected eruptive behavior.