DEPTH AND PRESSURES OF CRYSTALLIZATION OF MAGMA CHAMBERS BENEATH HAWAI'IAN VOLCANOES

The Hawai’ian Emperor Seamount Chain was formed by a mantle plume beginning about 80 Ma. The crust is raised by the plume while continuous eruptions form islands. As the islands begin to slide off the plume, they fall back to the sea floor, becoming a seamount. There are currently more than 80 undersea volcanoes stretching from the Aleutian Trench to the newly formed Loi’hi seamount. There are currently eight major islands which make up the state of Hawai’i. Seismic and other geophysical data have been used previously to determine the depth of magma chambers beneath Hawai’ian Volcanoes. Yang et al (1996) created a method in which three equations are used to calculate liquid compositions along the olivine-plagioclase-clinopyroxene coetectic. I used chemical analyses of glasses, which represent quenched liquid compositions, to calculate the pressure and temperature at which these liquids crystallize the minerals olivine, plagioclase, and clinopyroxene. The depth of crystallization can be calculated from these pressures. I then filtered the data, removing any classes that contained excess aluminum or water. Plotting the results for the filtered data set in CoPlot yields similar trends for all of the Hawai’ian Volcanoes in plots of CaO versus MgO, P versus MgO, T versus MgO, and depth versus MgO. The results agree with geophysical data, showing that the magma chambers lie at shallow depths, less than 10km at a pressure of about 1kilobar. Knowledge of the depths of chambers and pressures of crystallization is important for a number of reasons including understanding the chemical composition of molten rock that is flowing within the chamber and predicting when an eruption will occur.