The mantle sequence is 3-8 km thick (Dewandel et al. 2005) and is comprised of peridotite (~30% of the ophiolite) (Kelemen and Matter 2008), overlain by gabbros. The original crustal material is ...

That's when the geological record reveals plentiful ophiolites — bits of oceanic crust shoved onto continents — and blueschists, which are metamorphic rocks that form in subduction zones ...