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Chapter 7 Metamorphism and Metamorphic Rocks PowerPoint Presentation Stan Hatfield . Southwestern Illinois College Ken Pinzke . Southwestern Illinois College Charles Henderson . University of Calgary Tark Hamilton. Camosun College Copyright (c) 2005 Pearson Education Canada, Inc. 1 Metamorphosed Olympic Spirit Haircut Folded Proterozoic Gneisses: (~1.1 Ga) Barrie, Ontario Metamorphism The solid state recrystallization of one rock into another by a change in conditions unlike those in which it originally formed. Changing conditions include: Temperature, Pressure, Stress and Chemical Composition including fluids like H20 & CO2 Metamorphic rocks are produced from Igneous rocks Sedimentary rocks Other metamorphic rocks Paragneiss S. Greenland Gneisses are coarsely crystalline They have separate bands of mafic and felsic minerals They are formed by regional “dynamothermal” metamorphism under collisional orogens Agents of Metamorphism: Hydrostatic Pressure Differential Stress Agents of Metamorphism Shear flattening or rotation Confining versus directed pressure. Development of preferred orientations. Stretched Pebble Conglomerate Grade of Metamorphism & T°C Gradient Minerals Formed in Metamorphism Micas: Chlorite, Chloritoid, Talc Amphiboles: Tremolite, Actinolite, Glaucophane, Riebeckite Pyroxenes: Jadeite, Rhodonite Garnet: Almandine, Grossular, Spessartite Aluminosilicates: Andalusite, Kyanite, Sillimanite Others: Analcite, Cordierite, Corundum, Staurolite, Zeolites Al-Geobarometers, Fe-Mg Geothermometers Index Minerals & Grade for Pelitic Rocks Types of Metamorphism vs T°C Gradient Burial Metamorphism Alters Volcanics Zeolite Facies: Zeolites, Chlorite, Albite, Calcite Contact Metamorphism Bakes Sediments Cut by intrusion Or overlying Skarn Deposits: Cu/Fe, W Metamorphic Environments & Rocks Contact Metamorphism Clay + heat = hornfels (nonfoliated rock with mica and amphibole) Sometimes large metamorphic minerals impart a spotted appearance = porphyroblastic Quartzite and Marble often (not always) form by contact metamorphism from sandstone and limestone respectively Hornfels is named for the highest Temperature metamorphic mineral it contains : Chlorite, Cordierite, Pyroxene… Contact Metamorphism Cordierite Porphyroblasts In Shale Baked to Hornfels Contact (Thermal) Metamorphism: Shallow in Crust, dT>dP, Baking near Intrusions High Grade Regional Metamorphism Convergent Margins Orogenic Belts: Himalayas, Grenville, Appalachians Progressive Regional Metamorphism of Pelites Development of Foliation through Shear Dynamic Metamorphism Slaty Cleavage Developed By shear Leads to new Foliation Directions Prograde Metamorphism of Basalt With Normal Geothermal Gradients Low Medium High Upper Limit of Regional Metamorphism Migmatites: Partial Melting Of Low T°C Felsic Minerals Produces Granitic Melt & Residual Refractory Mafic Minerals Special Low dt/dP Subduction Zone Metamorphism of Basalt & Gabbro Glaucophane Na-Fe Amphibole Omphacite & Jadeite > 100 km Facies for Pelitic & Basaltic Rocks Metamorphic Facies & Tectonic Settings Dynamic Metamorphism: Strain >>T,P Breccia Shear ~1 Earthquake/Shallow Faults Mylonite Many Quakes/Deep Faults Geographic Locations of Metamorphics Convergent Margins Ancient Continental Shields Ancient Continental Shields: Acasta Gneiss 4.03 Ga Canadian Shield Slave Province NWT Impact Metamorphism 49,000 Years Ago 1.186 Km across Proterozoic Sudbury Impact Basin (1.85 Ga) Cuts Archean Gneisses (2.65 Ga) Ni, Cu, PGE Discovered 1883 Construction Of CPR Sudbury Impact Basin 1.85 Ga, Deformed in Grenville