GEOL 100 Lecture 7: Igneous Rocks
21 Feb 2019
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River valley has cut down into dark lava flows. When molten material cools after a long time = crystals are large. Lava vs. magma stays below surface, cools slowly due to insulation, magma exhumed, exposed in surface. Make it to earths surface and small crystals form. Cools a lot more slowly (thicker, more layers) Heating, needs a high pressure as well. Liquidus point at which a rock starts to melt under pressure and temperature conditions. Increase temperature above a mantle plume (hotter than what surrounds it) Hot water circulates in ridge, added in pres and in minerals. Hotter and/or less dense than surrounding material. Rises through cracks and conducts until density equalizes or it reaches the surface. Bubbles form and propel melt dissolved gasses. Texture: grain size, how much minerals are connected together. Composition (color): look at proportion of light vs. dark minerals. Lose heat to air, water, or underlying rocks. Can have a mix of cooling styles.
