The above cartoon is a cross sectional view showing a magnetic (island) are, a s

Question

The above cartoon is a cross sectional view showing a magnetic (island) are, a subduction zone. a spreading ridge, and a continent. Numbers 1 to 4 mark the location of a certain type of partial melting mechanism. Some of these numbers may repeat the same mechanism. Answer the questions 1 through 4 below corresponding to the number on the figure above and note well the additional guidance in terms of where the melting takes place (ie what sort of rock is partially melted and where). Partial melting lithosphere mantle occurs above a sub ducting oceanic plate at this location. Describe the melting process that occurs at this location (name the process AND describe it). Partial melting of mantle asthenosphere occurs here. Describe the melting process that occurs at this location (name the process AND describe it).

Explanation / Answer

1)Process name is Partial melting /decompression partial melting(synonyms of partial fusion) occurs in upper mantle.As temperature of mantle is raised above its solidus, percentage melting increases. At liquidus temperature, system is totally molten.  The temperatures of lithosphere are lower than solidus of ultramafic mantle to melt.

2) Process name is crustal anatexis: Continental crusts getthickened because of collisions among them. Within thick continental crust, wet, felsic and intermediate rocks undergo partial melting due to heating and compression. Compressing wet felsic rock can cause melting due to the slope of the wet felsic solidus.The resulting felsic magma cannot move quickly due to its viscosity.

3) Asthenosphere partial melting/basaltic volcanism: The basaltic magma is produced by partial melting of mantle in a concentrated zone of the asthenosphere.

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