Earth Sciences 1022A/B Lecture Notes - Lecture 5: Divergent Boundary, Oceanic Crust, Convergent Boundary
27 Apr 2019
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Document Summary
Where magma (igneous rocks) is generated: magma composition primarily related to degree of partial melting of asthenosphere rock. Convergent boundaries: magma produced by hydration melting (water driven from subducting oceanic plate lowers melting point of asthenosphere rock). The melted part is enriched in silica, producing magma of intermediate to felsic composition) Divergent boundaries: magma produced by decompression melting (melting of high-temperature asthenosphere under reduced pressure close to surface). More complete melting of silica-poor asthenosphere rock produces a magma of mafic composition. Intraplate hotspots (independent of plate boundaries): discrete heat plumes that locally melt high-temperature asthenosphere rock to produce a magma with a mafic composition. Butin continental areas, contamination of magma by molten continental crust can lead to a more felsic composition. Within the crust or as intrusive igneous rocks: Features formed by the ascent of magma (in this case, through a stack of layered sedimentary strata) Magma forming a blister -like body between strata.
