ERSC 1F90 Lecture Notes - Lecture 3: Phanerite, Pyroxene, Basalt
9 Apr 2015
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They"re formed from molten rocks that solidify (freezing of a melt) Forms quickly at the earth"s surface (fine-grained) or slowly within the lithosphere (coarse-grained; phaneritic) There is lots of evidence that indicates the parent material for igneous rocks (magma) is formed through partial melting. Partial melting occurs within the crust to the upper mantle, as far as 250 km deep. Melt: is called magma blow the surface and lava above. Igneous rocks were the first to form on the earth. Intrusive realm (underground) and extrusive realm (above the ground) Role of heat: rocks in the lower crust and upper mantle are near their melting points, the bulk of magma forms without additional heat, melting begins in confining pressure drops or if volatiles (fluids, gases) are introduced. Where does the heat originate: geothermal gradient: rate at which the earth"s temperature increases with depth, most (80%) heat is produced through radioactive decay of isotopes (potassium-
