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Rocks and Minerals

by: Lucious Kulas

Rocks and Minerals GEOL 320

Lucious Kulas
GPA 3.77


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This 8 page Class Notes was uploaded by Lucious Kulas on Monday October 5, 2015. The Class Notes belongs to GEOL 320 at Central Washington University taught by Mattinson in Fall. Since its upload, it has received 50 views. For similar materials see /class/218980/geol-320-central-washington-university in Geology at Central Washington University.


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Date Created: 10/05/15
GEOL 320 ROCKS amp MINERALS Fall 2009 Lecture 18 Metamorphism and Heat Flow Introduction amp De nitions Suggested reading from Blatt Tracy amp Owens Ch 17 p 339 341 1 Metamorphism Solid state transformation of preeXisting rocks due to change in pressure P and temperature T Mechanical Deformation Structural readjustment Chemical Recrystallization Mineralogical readjustment Low T Limit above 100 150 C gradational with diagenesis Hi gh T Limit below incipient melting typically 650 900 C 2 Agents of metamorphism A Temperature Thermal Contact Metamorphism eg adjacent to plutons B Pressure Differential Stress Dynamic Cataclastic metamorphism fault zone C Temperature amp Pressure Dynamothermal Regional Metamorphism Collision zone D Burial Load Burial Metamorphism Sedimentary Basin E Flux e g H20 Hydrothermal Metamorphism e g Ocean Ridge F Shock Impact metamorphism meteoriteasteroid impact 3 Types of metamorphism A Regional Metamorphism i Formed due to increase in both P and T ii Metamorphic rocks tend to show foliation Latin folia 2 leaves iii With increasing grade grain size increases iv Shale changes through slate slaty cleavage and schist schistosity to gneiss gneissose and granite melting rock name after structure B Contact thermal Metamorphism i Formed due to heat conduction from hot magma ii Forms an aureole around a magma chamber changes from high to low grade away from the contact iii Rocks tend to lack foliation massive hornfels C Metasomatism Change in original composition during metamorphism 4 Description Metamorphic Rocks A Protolith original rock Pelite basite calcareous ultramafic granitic i Derived from igneous rocks ortho ii Derived from sedimentary rocks para B Metamorphic Textures amp Structures i Fine lt1 mm Medium 1 3 mm amp Coarse grained gt3 mm ii Contact Metamorphism Granulose granoblastic hornfelsic iii Dynamic Metamorphism Cataclastic mylonitic iv Regional Metamorphism Deformation Foliation amp Lineation Slaty Cleavage Schistosity Gneissic Banding foliated S tectonite lineated L tectonite foliated and lineated L S tectonite C Metamorphic Assemblages function of P T amp X D Estimate P T conditions Metamorphic Facies E Progressive Zones amp Tectonic Setting From FS Spear 1995 Metamorphic Phase Equilibria and PressureTemperatureTime Paths Mineralogical Society of America 799 p l l nunnu Roots of the Himalayas r 60 E 5 Base of Archean crust E III Q D C P kbar Jil39 llll ll 0 200 400 600 800 1000 1203 Figure 11 A pressuretemperature diagram showing the general regions for metamorphism of the crust For reference the wet and dry melting curves for granite and basalt are also shown The approximate depths of the Archean crust 35 km and the deepest orogenic roots Himalayas are indicated to show the ranges of metamorphic conditions found in different settings From Kearey and Vine 1996 Global Tectonics Blackwell 333 p Volcanic High heat flow Trenchf line Anomalous mantle 400T 4000C 800 C 0 ContinentE j y 1200 c m 800 C 1200 C 200 km Olivine 1600quotC Spine 400 km S y I 600 km pine 17OOCC o Oxides 1700 C a iOOO C v 800 km 0 300 ih g km FIGURE 22 Hypothetical struc ture of a hydrothermal black smoker system underlying a spreading ridge From I R Cann quot and M R Sirens 1989 Modeling periodic megaplume emissions by black smoker systems Iour Geo W phys Research v 94 Fig 1 p 12 228 Reproduced by permission sul de deposit V ocean floor Spr Gadn9 a Xs lt a reaction zone magma chamber 1km From S Boggs Principles of Sedimentology and Stratigraphy Prentice Hall 774 p From Kearey and Vine 1996 Global Tectonics Blackwell 333 p Time at 5 mm a 1 Depth km 3Ma 8Ma l4Ma Fig 1038 Model of an extensional simple shear system in the upper and middle continental crust redrawn from Future upper plate of core complex 10 quot w 20 Future lower plate F exposed in core complex a F lS kmwvl t l lnctplentfaults lmbricately extended range 10 Future core complexquot upper plate 20 C rev 32 km l k s quotBreakawayquot quotCorecomplexquot Largefau bloc range range Basin range Basin Basin Preorogenic datum Fine elastic lacustrine Or ni ei sti s 098 C a C Coarse elastic Total extension 72 km 100 Highly attenuated ocks Ductile shear zone 165 Paleo depth of quotcore complexquot lower plate Wernicke 1985 with permission from the National Research Council of Canada Pressure 3 9 0 a Temperature FIGURE 179 Schematic pressure temperature diagram showing the actual PT paths taken by various rocks as they are buried and heated Burial heating and uplift phases of each path are indicated Also shown is the metamorphic field gradient see Figure 17 6 that effectively connects the ngx points on each PT path Many types of petrologic information can be used to constrain these paths 1 mineral inclusions in porphyroblasts 2 peak P and T from mineral equilibria 3 reset mineral equilibria stable isotope exchange isotopic cooling ages 4 range of fluid inclusion entrapment Modified from F S Spear l Selverstone D Hickmott P Crowley and K V Hodges 1984 Geology Fig l and E D Ghent M Z Stout and R R Parrish 1988 in E G Nisbet and C M R Fowler Heat Melamorphism and Tectonics Mineralogy Association of Canada Short Course Handbook 14 Fig 62 FIGURE 178 Cartoon of heat and fluid transfer by convection in the proximity of a shallow crustal pluton Convection cells of circulating meteoric fluids pick up heat from the pluton at or near a contact then disperse the heat through the aureole during a flow cycle Heating stage NOImal geotherm P max Burial stage 3 T W 2 3 T Uplift CH stage it Unroofing Temperature gt FIGURE 17 10 P T diagram illustrating actual processes involved in producing a typical clockwise metamorphic PT path The metamorphic field gradient is labeled MFG Normal geotherm Compression stage Pressure Heating stage 4 Temperature FIGURE 17 1 Counterclockwise P T path produced by regional scale magmatic heating in typical low pressure Buchan style terranes This mode of PT evolution has been suggested to explain regional anhydrous granulite facies terranes The metamorphic field gradient is labeled MFG Special Interest Box I ltl Lowgrade meta morphism of mudtock and the origin and migration of 01 Oil is Created from incompletely oxidized organic kcrogen transforms into the liquid hydrocarbon called crude oil At this point crude oil is a sticky viscous liqutd that is nely persed among and stuck to t c grains of clay and other sedimentary particles in the basin Au Oil Well drilled Lnto this material would recover no oil because the crude oil is too vtdely dispemed and the molecules adhere to the sedimenb nry grains Therefore the oil cannot llow through move tom the clnyrt39ich source rock and eventually concentrate elsewhere Aclay mineral called 39 E L ttnt clny formed by weathering and thus the most abundant clay deposited in sedimentary basins Smectite converts meramorphienlly into another clay called illite us the T rises From about 50 to 100 C duting burial in sedimentary basins Therefore illitc is the most nbundttnt constituent of shulest Smecritc contuins about 40 water by volume illite contnins only it few percent Thus as smectite converts to illite large quantities of water are lor utct liquid oil The forcibly expelled water then ushes the oil from the clayrtch source rock and causes it to migrate into reservoirs ll39lytlrnulic fractures likely play an important role in this migration Calculations of the amount of energy required to convert kcmgen to oil in sedimentary basins show that in most basins there is not enough thermal energy available to form liquid oil in the T rnngc 100 The conversion should not occur until much higher temperatures are attained Yet 50 0 C is the T rurth of observed oil formation in most sedimentary basins Recent experiments and theoretical work show that the reaction in which Smcclitc converts to illite acts as a catalyst that cattsas transformation ofkcrnr reaction without being permanently changed by the reaction This research on clay mineral reactions in sedi mentnry basins suggests that in many of the world39s great oilproducing basins lowturtle burial ntetn mo hism of clay numerals is important to both the formation of oil and the migration of oil from source rocks to reservoirs l39 pl lrom Matem Fltvurnl Geology by Graham R Thompson and Jonathan Turk copyright 991 by Saunders College Publishtng reprinted by permission of the publisher Special Interest Box I66 Decal39bonalion reactions and CO2 ux Into the atmosphere paleoatmospheric in uences Kerrick and Caldeira ll993 see also Ingebt39jtscn m Manning 1999 have postulated that metamorr phism during orngeny can release sttFlicient CO via lecurlmudtion reactions to signi cantly alter the potentizrltll39l se cgassing of IL toeczuuc tidgcsystems 05 x to gy 21ml from vulcuuit arcs I10 gyl Continental extcn siotml regimes C also a potential art for signi eum ux into the ntnmsplme from Ll u m tatlon retic t 39 eeply circulating meteoric water in the fractured U39HSL n n g c From MG Best 2003 Igneous and Meta morphic Petrology Blackwell 729 p GEOL 320 ROCKS amp MINERALS Lectures 2324 Metamorphic Reactions amp Chemographic Projections Suggested reading from Blatt Tracy amp Owens Ch 19 p 384 394 1 A Chemographic or compatibility diagram refers to a graphical representation of rock bulk compositions mineral compositions and stable mineral assemblages for given physical conditions For convenience of 2 D plotting in a triangular diagram the number of components must be reduced to 3 yet real rocks contain many more than this Therefore some components must be combined and others omitted Bearing in mind these assumptions and the compromise to thermodynamic rigor that can result chemographic projections provide valuable graphical representations of metamorphic reactions and mineral assemblages 2 The Phase Rule The thermodynamic basis of chemographic diagrams is the phase rule P F C 2 The occurrence of characteristic mineral assemblages in metamorphic zones indicates that these assemblages are stable over a range of P T i X that is F 2 2 so the phase rule can be re written C 2 P the number of phases is equal to or less than the number of components This is known as Goldschmidt s mineralogical phase rule 3 Choice of components the ACF diagram In order to graphically display mineral assemblages and reactions in complex rocks Finnish petrologist Pentti Eskola 1883 1964 developed the ACF diagram This diagram uses only the components necessary to describe the minerals that appear and disappear during metamorphism and thus are sensitive indicators of metamorphic grade minerals that are stable over a wide range of metamorphism eg quartz albite K feldspar micas magnetite apatite are ignored The three components used for the diagram simplified for the purposes of this class are A A1203 NaZO K20 C CaO F FeO MgO These components are convenient because they group chemically similar elements complete solid solution between Fe and Mg 4 Types of Reactions There are two types of reaction configurations in ternary systems where all phases are of fixed composition no solid solution Terminal stability reaction A B C D One phase plots within the triangle formed by the other three At conditions where the left hand side of the reaction is stable phase D is not stable anywhere on the diagram Tie line ip reaction B C A D The four phases plot as a quadIilateral so no phase plots internally to the other three This reaction is not terminal because all phases are still present on both sides of the reaction but mineral compatibilities have changed The mineral assemblage in a rock can also change as minerals that exhibit solid solution change their compositions continuously as pressure and temperature change 5 Other Diagrams The ACF diagram is convenient for mafic rocks but other diagrams have been developed for different rock types notably the AKFM diagram developed by Thompson for pelites and the SiOz CaO MgO diagram for calc silicates and ultramafic rocks you will use this diagram on your lab exercise ABC D P and T constant n P and T constant Figure 829 One of the two general types of heterogeneous reactions in a ternary system where phases are all of xed composition This type is called a terminal stability reaction or a piercing point reaction BC A D gt P and T constant P and T constant Figure 830 The other of the two general types of heterogeneous reactions in a ternary system where all phases are fixed composition This type is called a tie line ip or a crossing tie line reaction Figure I 1131 a ACFN diagram and b ACF diagram for the lower blueschist facies The diagnpstic association is lawsonite glaucophane which occurs in several different assemblages r From FS Spear 1995 Metamorphic Phase Equilibria and PressureTemperatureTime Paths Mineralogical Society of America 799 p


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