EARTH121 Lecture Notes - Lecture 4: Sedimentary Structures, Mafic, Source Rock
25 Aug 2016
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Classifying igneous rocks: colour (mafic or melsic, composition (% of each type of mineral, texture (grain size) Magma: three components: solid, liquids and gas, solid masses change composition, liquid: the melt itself is composed of mobile ions (mostly si and o, different mixes of elements yield different magmas, gases (o,co2, h2o(g)) Types: felsic (66 76% sio2, intermediate (52 66%, mafic (45 52%, ultramafic (38 45%, defined by percentage of silica (determines type of magma and rock) Magma only forms in special tectonic settings: partial melting occurs in the crust and upper mantle, melting is caused by. Heat transfer (heat from different sources impact its surroundings and can create magma: pressure release. Pressure drops when hot rock is carried to shallower depths. Mantle plumes: (usually middle of continental plates) Beneath rifts: lithosphere is thinning, translation to shallower depths = melting. Under mid-ocean ridges: materials make it up near the ridge where it is shallower. Convergent boundaries: addition of volatiles (flux melting)
