Hawaiian xenolith populations, magma supply rates, and development of magma chambers

Abstract

Hawaiian volcanoes pass through a sequence of four eruptive stages characterized by distinct lava types, magma supply rates, and xenolith populations. Magma supply rates are low in the earliest and two latest alkalic stages and high in the tholeiitic second stage. Magma storage reservoirs develop at shallow and intermediate depths as the magma supply rate increases during the earliest stage; magma in these reservoirs solidifies as the supply rate declines during the alkalic third stage. These magma storage reservoirs function as hydraulic filters and remove dense xenoliths that the ascending magma has entrained. During the earliest and latest stages, no magma storage zone exists, and mantle xenoliths of lherzolite are carried to the surface in primitive alkalic lava. During the tholeiitic second stage, magma storage reservoirs develop and persist both at the base of the ocean crust and 3–7 km below the caldera; only xenoliths of shallow origin are carried to the surface by differentiated lava. During the alkalic third stage, magma in the shallow subcaldera reservoir solidifies, and crustal xenoliths, including oceanic-crustal rocks, are carried to the surface in lava that fractionates in an intermediate-depth reservoir. Worldwide xenolith populations in tholeiitic and alkalic lava may reflect the presence or absence of subvolcanic magma storage reservoirs.