Pressures of Crystallization of Icelandic Magmas

Iceland lies astride the Mid-Atlantic Ridge and was created by sea-floor spreading that began about 55Ma.The crust is anomalously thick (20^40 km), indicating higher melt productivity in the underlying mantle compared with normal ridge segments as a result of the presence of a mantle plume or upwelling centered beneath the northwestern edge of the Vatnajo « kull ice sheet. Seismic and volcanic activity is concentrated in 50 km wide neovolcanic or rift zones, which mark the subaerial Mid-Atlantic Ridge, and in three flank zones. Geodetic and geophysical studies provide evidence for magma chambers located over a range of depths (15^21km) in the crust, with shallow magma chambers beneath some volcanic centers (Katla, Grimsvo « tn, Eyjafjallajo « kull), and both shallow and deep chambers beneath others (e.g. Krafla and Askja).We have compiled analyses of basalt glass with geochemical characteristics indicating crystallization of ol^plag^cpx from 28 volcanic centers in th