The rapid, deep burial of sediments in an accretionary prism leads to the formation of a metamorphic rock termed blueschist gneiss greenschist migmatite

The rapid, deep burial of sediments in an accretionary prism leads to the formation of a metamorphic rock termed blueschist.

Blueschist is a metamorphic rock formed at subduction zone in high pressure which corresponds to 15 km - 30 km depth and a low temperature ranging from 200°C - 500°C. The protolith rock is the sedimentary rock called basalt or rocks with similar composition. The blue colour is due to the presence of minerals lawsonite and glaucophane.  

It can also have other colours such as black, blue-green and grey. For blueschist to make it to the surface, it must be exhumed carefully to prevent it from returning to the earth's interior due to the balance of thermal conditions with other rocks formed in similar facies condition.

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