CEE 1030 1nd Edition Lecture 7 Metamorphic Rocks Outline of Last Lecture I Review II Sedimentary rocks III Sediments vs sedimentary rocks IV Types of sedimentary rock a Detrital b Chemical c Organic V Sedimentary structures VI Sedimentary environments a Sedimentary facies Outline of Current Lecture I Metamorphic rocks a Agents of metamorphism II Metamorphic textures III Metamorphic grade IV Metamorphic environments Current Lecture I Metamorphic rocks a Changes in mineralogy texture b Often the chemical composition of solid rock is subjected to conditions very different to those in which it was initially formed c Effects of metamorphism depends on parent rock protolith d Agents of metamorphism i Heat 1 Provides energy for chemical reactions chemical reactions occur at a faster rate 2 Recrystallization of existing minerals 3 Formation of new stable minerals 4 Sources of heat a Geothermal gradient temperature increases with depth b Local intrusion of magma ii Pressure 1 Also increases with depth as thickness of overlying rocks increases These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II 2 Confining pressure applies force equally in all directions produces a more compact dense rock 3 Directed pressure or differential stress forces unequal in different directions producing a deformed rock iii Fluids 1 Chemically active fluids mainly water with other volatiles 2 Chemical reactions take place faster at lower temperatures in the presence of water changes the composition of rock 3 Sources of fluids a Hydrated minerals clays and micas b Fluids from magma intrusions c Pore waters in sedimentary rocks Metamorphic textures a Physical changes during metamorphism b Texture size shape arrangement of mineral grains c Reorientation of rod or plate shaped crystals d Recrystallization of minerals resulting in fewer but larger grains e Reorientation of mineral grains f Porphyroblastic texture i Large grains surrounded by fine grained matrix of other minerals ii Recrystallization small g Foliation any planar arrangement of mineral grains or structural features within a rock i Rotation of platy and or elongated minerals ii Rock or slaty cleavage closely spaced planar surfaces along which rocks easily split into thin tabular sheets iii Recrystallization and alignment of mica grains quartz and feldspar are not affected iv Slate very fine grained rock generated mainly from low grade metamorphism of shale or mudstone 1 Most pool tables are made of slate v Schistosity higher metamorphic grade larger crystals vi Phyllite platy minerals larger than in slate but not quite large enough to see with the naked eye vii Schist medium to coarse grained rock platy minerals predominate viii Gneiss parent rock is schist granite volcanic medium to coarse grained rock 1 Banded appearance gneissic texture ix Migmatite transition from high grade metamorphic rock to igneous rock h Non foliated texture i Marble parent rock is limestone or dolostone III IV ii Quartzite parent rock is quartz rich sandstone quartz grains fused together to a very hard rock Metamorphic grade a Effects of increasing metamorphic grade i Increasing intensity of metamorphism ii Increasing crystal size iii Increasing coarseness of foliation b Index minerals certain minerals are good indicators of metamorphic conditions minerals formed depend on original rock type Metamorphic environments a Geothermal gradient and burial metamorphism increase in temperature with depth b Contact or thermal metamorphism increase in heat due to intrusion of hot magma i Local effect ii Zone of alteration called an aureole forms in country rock around intrusion 1 Hornfels general term for rather hard nonfoliated metamorphic rocks formed in aureole 2 Similar to firing clay in a kiln c Hyrdrothermal metamorphism chemical alteration as hot iron rich fluids circulate through fissures and cracks that develop in rocks i Most widespread along mid ocean ridge system d Impact metamorphism meteorites hit Earth at high velocity create shock and pressure waves e Regional metamorphism greatest quantities of metamorphic rocks occurs when rocks are squeezed between two plates as they converge during mountain building