Describe the sequence and composition of an Ophiolite and evaluate its use in understanding the Oceanic Lithosphere

Ophiolites always follow a particular sequence and composition, the first layer is comprised of deep sea pelagic sediments (often red clays or greywackes) beneath this layer is a layer of Basaltic Pillow lavas containing augite and plagioclase. The layer of Pillow lavas is the first but certainly not the last layer of igneous rock contained within an Ophiolite, the second being a layer of Dykes directly beneath the Pillow lavas (once comrprised of Basaltic magma). The next layer is made up of intrusive Plutons, this igneous material is mafic but due to its much slower cooling often has large crystals which the volcanic layers above do not contain. Beneath the Plutonic intrusions lies the Residual Mantle, this layer can be anywhere up to 10km thick and is comprised of Ultramafic material. The final layer of an Ophiolite is known as the Metamorphic Sole, this layer is by far the thickest ranging from 10's of Kilometres to hundreds. This final layer is composed of highly deformed and foliated upper layers of the mantle.

Ophiolites are incredibly useful as they allow us to examine the Oceanic Crust in its entirety without having to drill potentiall hundreds of Kilometres down (which is impractical) or resorting to geophysical techniques which can show us the composition of these structures but are nowhere near as reliable as having a real specimen. The validity of Ophiolite data is confirmed by dredging and drilling, most of the time Ophiolites are deemed to be very valid but subtle differences are often found between Ophiolites and current Oceanic Lithosphere. These differences however are the result of these sections of Oceanic Lithosphere being weathered to a very different degree to the Ophiolites paired with Regional Metamorphism vastly skewing results.