Tholeiitic

Geologic context

Tholeiitic rocks are the most common igneous rocks in Earth's crust, produced by submarine volcanism at mid-ocean ridges and make up much of the ocean crust. Tholeiitic basaltic magmas are initially generated as partial melts of lherzolite (olivine, enstatite and diopside) produced by decompression melting of the Earth's mantle. Tholeiitic basalt constituting the oceanic crust is termed MORB:mid-ocean-ridge basalt. Throughout the process of igneous differentiation, the oceanic crust acts to reduce the magma, producing the tholeiitic trend. In contrast, alkali basalts are not typical of ocean ridges, but are erupted on some oceanic islands and on continents, as also is tholeiitic basalt. Because the Moon is extremely reduced, all of its basalts are tholeiitic.