Gabbro

Abstract

Gabbros are the most common rocks in the oceanic crust and form its lower part (layer 3). They represent slowly cooled crystal mushes composed mainly of olivine, plagioclase, and clinopyroxene, corresponding to the accumulated phases during differentiation of primitive MORB in shallow magma chambers under the ridges. Their mode of accretion is strongly controlled by the spreading rate, with the formation of layered gabbros at fast-spreading ridges and more isotropic gabbros at slow-spreading ridges. The latter often show signs of plastic deformation and vast crystallization of evolved interstitial parageneses.