Assimilation of the Mantle and Altered Crust by Oceanic Magmas

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Assimilation of igneous, metamorphic, and sedimentary rocks by basalt magma is an unavoidable consequence of volcanic activity, and the presence of xenoliths (foreign rock fragments) in ocean island and propagating ocean rifts is evidence that assimilation does occur during oceanic volcanism. The process of assimilation is poorly understood and whether melting, disintegration, or diffusion into or out of the material being assimilated is the dominant process will depend on the type of material being assimilated, on the kinetics of magma interaction with that material, and on the temperature and composition of the magma. The experiments supported here will investigate the first of these problems; the melting, disintegration, or diffusion from various mantle minerals and alteration minerals, when placed in contact with molten basalt. The products of the experiments will be chemically analyzed by electron microprobe and isotope dilution mass spectrometry. Preliminary experiments have produced unexpected and interesting results, and further work will determine the importance of assimulation to the major and trace element chemistry of seamount, ocean island, and propagating rift basalts. This project will be supported at $120,470 for 2 years.