GEOL 101 : Igneous Rocks and Processes
GEOL 101 : Igneous Rocks and Processes 101-017
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This 4 page Class Notes was uploaded by Natalee Stanton on Wednesday February 3, 2016. The Class Notes belongs to 101-017 at University of South Carolina taught by in Winter 2016. Since its upload, it has received 25 views. For similar materials see Geology 101-017 in Geology at University of South Carolina.
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Date Created: 02/03/16
GEOL 101: Igneous rocks: Solids form melts Igneous Rocks ignis = fire (Latin) Formed by the solidification of magma Originate deep in the crust or upper mantle Form most of the crust How do magmas form? o When rocks melt (or partially melt) When do rocks melt? o When the temperature exceeds the melting point of the rock or some minerals within the rock for a given pressure and composition. Variables of state All matter exists as either o Solid o Liquid o Gas Temperature – increase with depth Pressure – increases with depth Composition combination of elements Partial Melting Occurs when some mineral s in a rock melt at lower temperatures than other mineral in the same rock Temperature of 1000C required for partial melting of crustal rocks Depth of >40 km required for temperatures of 1000C Factors affecting melting of minerals (and Rock) Pressure – increased pressure raises melting points Water content – increased water content lowers melting points Rock composition – felsic minerals melt at lower temperatures than mafic minerals Composition and classification of igneous rocks Chemistry (silicon dioxide ) (Quartz) o Range from 40 to 70% Mineralogy: o Felsic (Feldspar, silica) o Intermediate o Mafic (magnesium – ferric) o Ultramafic How do igneous rocks differ from one another? Texture – sixe of crystals o Coarse grained rocks – when magma has time to cool o Fine – grained rocks when the magma cools quickly o Mixed texture rocks Texture is related to rate o cooling o Intrusive igneous rocks – large crystals – cools beneath the surface and has time to cool o Extrusive igneous rocks – small crystals – magma come up to the surface and cools quickly Ash – volcanic magma that cools so quickly that it turns into class Partial melting and the origin of magmas Partial melting of upper mantle – at divergent spreading centers o Mafic magmas Partial melting of sedimentary rocks and mafic lithosphere – in subduction zone o Intermediate magmas Partial melting of continental crust o Felsic magmas The Fate of Magma 1. Partial melting 2. Magma rises 3. Magma pools in magma chamber o intrusive rock 4. Magma erupted at surface o extrusive rock Why are there so many types of igneous rocks? Magmatic differentiation o Process by which rocks of carious compositions arise from a uniform parent magma o Occurs because different minerals crystallize at different temperatures (al) Fractional crystallization The process by which crystals forming in a cooling magma are segregated form the remaining magma The first minerals that crystallize from a cooling magma are the ones that were the last to melt Basaltic magmas will gradually cool and differentiate into a more felsic melt Forms of magmatic intrusions Plutons o Discordant intrusion Batholiths – a lot of plutons put together Stocks o Concordant intrusions Sills – magma intrudes parallel to other sedimentary rocks Dikes – cut across layers of country rock Veins – smaller running Igneous activity and plate tectonics Magmatic systems o Mid ocean ridges – divergent boundaries – mantle upwelling o Island arc – subduction – oceanic plate subduction o Continental arc – oceanic plate subduction o Hot –stop volcanism – mantel plume ex Hawaii Sample Exam Questions: Minerals form as a result of: a. Crystallization form a magma b. Recrystallization in the solid state c. Precipitation from solution d. All of the above The two characteristics used to describe a rock are: a. Texture and hardness b. Color and taste c. Hardness and mineralogy d. Mineralogy and texture Where would you expect to find the largest crystals in a lava flow? a. Near the top surface of the flow b. In the center of the flow c. Near the bottom surface of the flow d. The crystals would be the same size throughout Large igneous bodies that form at depth in the Earth’s crust are called ______. a. Dikes b. Plutons c. Sills d. veins Andesite is an example of a(n) ______ igneous rock. a. Felsic b. Intermediate c. Mafic d. Ultramafic
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