ENVS 1050 Lecture 4: Week 4 - Igneous Rocks
21 Mar 2016
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Document Summary
Can be intrusive (at depth) or extrusive (at surface) Intrusive processes are for the most part inferred indirectly based on mineralogy, contact with country rock and lab experiments. Texture: size, shape and arrangement of grain. Vesicular: holes from gas bubbling through rock during solidification. Fragmental: - dust/ash: < 2mm (all 3 are extrusive) Texture is a function of viscosity and rate of cooling: fine grained: more viscous, cools quickly (often at surface, coarse grained: less viscous, cools slowly (often at depth) Chemical composition of rock = chemical composition of magma. Mafic: low silica ~50%, high fe, mg, ca. Felsic: high silica ~65%, low fe, mg, ca. Ultramafic: silica ~45%, very high fe, mg, ca. Tabular structures concordant (sills) or discordant (dikes) with layering of country rock. Stock: small pluton exposed at surface, < 100km2. Batholith: large pluton exposed at surface, > 100km2. Granite will melt at 650oc, basalt at 1000oc. Water as a gas under pressure decreases melting point.
