GEOL 212 Lecture Notes - Lecture 51: Diorite, Olivine, Volcanism
26 Dec 2017
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Document Summary
Where does magma form on earth: mid-ocean ridges: rising rocks in mantle convection cell bring heat near the surface, transfering heat to overlying rocks. At the same time, the hot rising mantle rocks experience decompression melting. As in mid-ocean ridges, hot spot rocks transfer heat to overlying rocks and experience decompression as they come up: subduction zones: as oceanic crust sits at bottom of ocean, it becomes charged with sea water. Subducting slabs, although relatively cold, dive into hot surrounding rock. The slab acts as conveyors drawing water into the hotter, drier asthenosphere. When the water percolates into the surrounding hot rocks, melting due to the infusion of volatiles occurs. This leads to some interesting consequences: subduction zone magmas tend to be low temperature magmas compared to those from the other regions. Because they are, they are compositionally enriched in. These magmas are the ultimate origin of continental crust: we said earlier that venus apparantly has no subduction zones.
