GEOL107 Study Guide - Midterm Guide: Mafic, Basalt, Porphyritic
26 Sep 2017
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Document Summary
Igneous rocks and volcanoes chapter 4 in . Igneous - origin from cooling and subsequent crystallization (solidification) of magma. Magma - hot (>1100c), liquid, melt of elements. Major elements present are o,si,al, fe, ca, na, k and mg. Magmas have range of varying compositions, two general end member type of. Composed of ~50% silica (sio2), have higher amounts (up to 30%) iron, magnesium and calcium, and lower amounts (about 3%) potassium, sodium, and dissolved gases. Silicic (felsic) magmas composed of ~65-77% sio2, have lower amounts (5-6%) iron, magnesium and calcium, and higher amounts (up to 10%) of potassium, sodium and dissolved gases. Passive eruption of basaltic (mafic) magma (lower silica and gas. Violent eruption of silicic (felsic) magma (higher silica and gas content. Amount of silica and dissolved gases in magma have effects on eruption style. Harder to get higher viscosity magmas to erupt at surface - instead of flowing out, must.
