Anything on the solidus line that is moved upwards due to mantle upwelling (decompression melting) will then turn to liquid. This graph explains why decompression melting works. However, the mantle must move enough to reach the liquidus line. If it only moves a little bit, and doesn’t reach the next line, it won’t melt completely. Often, the mantle will be in a state of partial liquids and partial solidus. Subducting slabs come from the surface, which is at a much colder temperature then the mantle. Nonetheless, we still observe magma formation due to melting of the subducting slab. The friction of the subducting slab also causes a small amount of heating, but is not the source of melting. The source of melting for the subducting plate is water. If the subducting plate has water content, the melting point of the solidus is much lower. The above geotherm assumes the conditions are anhydrous. However, if there is water present then things melt much easier. Subducting plates often come from ocean, which causes them to have high water content.Here the subducting plate is under the ocean. This drags down seawater, which hydrates them. Note the different geotherms for hydrated and dehydrated plate melting. The hydrated form melts much easier.Amphibole can be considered a hydrated form of pyroxcine. When water is added, this transformation can occur. As amphibole is heated, it realeases its water, and dehydrates back into pyroxcine. This water is released into the surrounding mantle.
7)Sketch Bowen’s reaction series and use them to explain the process and effects of fractional crystallization.