Basalt is the most voluminous of all the igneous rocks. Extensive field,
experimental, petrographic and geochemical studies of basalt have
provided us with a considerable understanding of igneous petrogenesis,
plate tectonics, and crust-mantle interaction and exchange. One
important aspect of geology that has developed over the last few decades
is the study of oceanic basalts. The ocean basins cover about two thirds
of the earth's surface and are floored by a basement of oceanic basalt
that is continuously undergoing generation at spreading centres and
destruction at subduction zones, a process which throughout geological
time is recognized as the principal means of generating new crust. The
study of oceanic basalts enables us to understand better the generation
and recycling of crustal materials (including the continental crust),
and the exchange between oceanic crust and seawater via hydrothermal
activity. Compositional variations displayed by oceanic basalts provide
windows into the mantle, and the identification of isotopically-distinct
mantle reservoirs demonstrates that the source of oceanic basalts is
heterogeneous and is controlled by convection and reservoir interactions
within the mantle.
