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USGS CMG InfoBank: Other Plutonic Igneous Rocks

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Comment: 16:24 - 17:40 (01:16)
Source: Annenberg/CPB Resources - Earth Revealed - 14. Intrusive Igneous Rocks
Keywords: continent, crust, mantle, subduction, andesite, diorite, "convergent plate", melting, upwelling, basalt, "lava flow", crust, felsic, viscosity, volcano, pluton, "David Sigurdson"

Our transcription: In fact, partial melting of continental crust, mantle, and subducting slabs probably all contribute to the formation of andesite and diorite.
But these aren't the only igneous rocks that form at convergent plate boundaries.
Many other types also occur.
Partial melting in the mantle triggered by upwelling associated with subduction will form basaltic magma.
This magma may collect, cool, and harden at the base of the crust.
In some cases though, the magma may move rapidly up towards the surface, still of basaltic composition, and erupt as a basaltic lava at the Earth's surface.
If it is held for some time within the Earth's crust, assimilation may take place.
ILarge amounts of the crust may be melted and incorporated into this magma so that it becomes higher in felsic constituents.
These felsic constituents then increase the viscosity so that the magma does not so easily move up to the surface to erupt as a volcano.
Instead, it lodges itself within the crust of the Earth as a pluton.

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