 In either case, the unsettled asthenosphere might have experienced low degrees of decompressional melting and interacted with North American lithosphere to yield within plate compositions.The composition of some lava flows in the Wells Gray-Clearwater volcanic field is unusual because they include small, angular to rounded fragments of rock called nodules and crystals that come from the mantle.These green nodules are known as peridotites because they are mostly made of a magnesium iron silicate mineral called olivine.