Magma Underplating Of Continental Crust

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Journal Article: Magma Underplating Of Continental Crust

Experiments conducted over the past decade have shown that common mantle melting products have densities at Moho pressures that exceed the density of average continental crust. In a situation of perfect gravitational equilibrium, they would not rise to or near the surface. The exact behaviour reflects the coupling of crust to the mantle, strong at early periods of magmatic cycle, but weak at more evolved stages where crustal melting and degassing commences. Spreading of underplate magmas in rift zones, above subduction zones or even hot spots, may perturb the state of the crust over very large areas. Where dense magmas occur beneath normal 30-km continental crust, they may crystallize to form gabbro-peridotiteanorthosite complexes. Dense crustal components may founder with melting, assimilation and degassing producing very high-temperature fluids rich in H2O-CO2-CO and S-halogen species depending on compositions. The process acts as density filter cleaning the crust and lowering its mean density. This process must have been particularly efficient during the Archean when komatiite magmas were common. Opportunities for magma contamination and mixing processes must abound in situations of large-scale underplating. When crust is overthickened, underplate magmas may crystallize to products with eclogitic affinity with the possibility of their foundering in normal mantle.

W. S. Fyfe

Published Journal 
Journal of Volcanology and Geothermal Research, 1992

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W. S. Fyfe. 1992. Magma Underplating Of Continental Crust. Journal of Volcanology and Geothermal Research. (!) .