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.
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 “dynamo-thermal” 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 Mylonite Shear ~1 Earthquake/Shallow Faults Many Quakes/Deep Faults
Geographic Locations of Metamorphics Ancient Continental Shields 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
Ni, Cu, PGE Discovered 1883 Construction Of CPR Proterozoic Sudbury Impact Basin (1.85 Ga) Cuts Archean Gneisses (2.65 Ga) Ni, Cu, PGE Discovered 1883 Construction Of CPR Grenville Orogeny is called the Penokean Orogeny ~ 1.16 Ga Sudbury Impact Basin 1.85 Ga, Deformed in Grenville