A sheeted dyke complex or sheeted dike complex is a normal component of an ophiolite, a piece of oceanic crust that has been emplaced within a sequence of continental rocks. The dykes

Dike (geology)

A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...

 act as feeders for the overlying sequence of extrusive rocks typically pillow lava

Pillow lava

Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava under water, or subaqueous extrusion. Pillow lavas in volcanic rock are characterized by thick sequences of discontinuous pillow-shaped masses, commonly up to one metre in...

s, together forming layer 2 of the oceanic crust

Oceanic crust

Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...

. As each injection of a dyke represents one increment of seafloor spreading, each dyke is normally intruded into earlier dykes. The dykes are typically dolerites but plagiogranites (trondhjemite

Trondhjemite

Trondhjemite is a leucocratic intrusive igneous rock. It is a variety of tonalite in which the plagioclase is mostly in the form of oligoclase. Trondhjemites are sometimes known as plagiogranites....

s) often form a significant part of the complex.