Seeing Beyond the Melt Lens Into Crustal Accretion Processes at Mid-Ocean Ridges
ORI Funded Research: 2011
Ocean crust is generally thought to form from crystallization of melts as they ascend from the mantle, cool, and crystallize, however, the details and depths over which this process occurs is not well understood. Constraints on crustal accretion have been derived from textural and petrologic observations in ophiolites, models of hydrothermal cooling, and geophysical studies at the ridge axes. However, due to mixing and homogenization in axial magma chambers, very few geochemical studies of lavas erupted on-axis can provide insights into processes occurring beneath the melt lens on fast- and intermediate-spreading centers. Here, we propose to use melt inclusions trapped in olivine phenocrysts from the East Pacific Rise and Juan de Fuca ridge to see beyond the melt lens into the lower ocean crust on fast- and intermediate-spreading centers. Volatile analyses of melt inclusions will be used to calculate the pressure (or depth) of crystallization, which will provide constraints on where crustal accretion takes place. These results will be combined with major and trace element analyses of the melt inclusions to determine how melt evolves during ascent through the oceanic crust. This study will provide a different perspective on outstanding questions on magma differentiation during ascent from the mantle, melt-rock reaction in the lower crust, the depth of crystallization, and the creation of oceanic crust at mid-ocean ridges. Furthermore, the results of the proposed study will ultimately lead to a better understanding of processes occurring in the lower oceanic crust that can be applied to more complicated ridge settings in future studies.