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Copyright (c) 2005 Pearson Education Canada, Inc. 1
PowerPoint PresentationPowerPoint PresentationStan Hatfield . Stan Hatfield . Southwestern Southwestern
Illinois CollegeIllinois College
Ken Pinzke . Ken Pinzke . Southwestern Illinois Southwestern Illinois CollegeCollege
Charles Henderson . Charles Henderson . University of University of CalgaryCalgary
Tark Hamilton. Tark Hamilton. Camosun CollegeCamosun College
Chapter 7Chapter 7
Metamorphism Metamorphism and Metamorphic and Metamorphic
RocksRocks
Folded Proterozoic GneissesFolded Proterozoic Gneisses: : (~1.1 Ga) (~1.1 Ga) Barrie, OntarioBarrie, Ontario
MetamorphismMetamorphism The The solid state recrystallizationsolid state recrystallization of one of one
rock into another by a change in rock into another by a change in conditions unlike those in which it conditions unlike those in which it originally formed.originally formed.
Changing conditions include: Changing conditions include: TemperatureTemperature, , PressurePressure, , StressStress and and Chemical CompositionChemical Composition including fluids including fluids like H20 & CO2like H20 & CO2
Metamorphic rocks are produced fromMetamorphic rocks are produced from Igneous rocksIgneous rocks Sedimentary rocksSedimentary rocks Other metamorphic rocksOther metamorphic rocks
ParagneissParagneissS. GreenlandS. Greenland
Gneisses are Gneisses are coarsely crystallinecoarsely crystalline
They have They have separate bands of separate bands of maficmafic and and felsicfelsic mineralsminerals
They are formed They are formed by by regional regional “dynamo-thermal”“dynamo-thermal” metamorphism metamorphism under collisional under collisional orogensorogens
Agents ofAgents of MetamorphiMetamorphi
sm:sm:
Hydrostatic Hydrostatic PressurePressure
Differential Differential StressStress
Agents of MetamorphismAgents of Metamorphism
Confining versus directed pressure. Development of preferred orientations.
Shear flatteningor rotation
Minerals Formed in Minerals Formed in MetamorphismMetamorphism
Micas: Chlorite, Chloritoid, TalcMicas: Chlorite, Chloritoid, Talc Amphiboles: Tremolite, Actinolite, Amphiboles: Tremolite, Actinolite,
Glaucophane, RiebeckiteGlaucophane, Riebeckite Pyroxenes: Jadeite, RhodonitePyroxenes: Jadeite, Rhodonite Garnet: Almandine, Grossular, SpessartiteGarnet: Almandine, Grossular, Spessartite Aluminosilicates: Andalusite, Kyanite, Aluminosilicates: Andalusite, Kyanite,
SillimaniteSillimanite Others: Analcite, Cordierite, Corundum, Others: Analcite, Cordierite, Corundum,
Staurolite, ZeolitesStaurolite, Zeolites
Al-Geobarometers, Fe-Mg GeothermometersAl-Geobarometers, Fe-Mg Geothermometers
Contact MetamorphismContact Metamorphism Clay + heat = Clay + heat = hornfelshornfels (nonfoliated rock (nonfoliated rock with mica and amphibole)with mica and amphibole)
Sometimes large metamorphic minerals Sometimes large metamorphic minerals impart a spotted appearance = impart a spotted appearance = porphyroblasticporphyroblastic
Quartzite and Marble often (not always) Quartzite and Marble often (not always) form by contact metamorphism from form by contact metamorphism from sandstone and limestone respectivelysandstone and limestone respectively
Hornfels is named for the highest Hornfels is named for the highest Temperature metamorphic mineral it Temperature metamorphic mineral it contains : Chlorite, Cordierite, contains : Chlorite, Cordierite, Pyroxene…Pyroxene…
Metamorphic Environments Metamorphic Environments & Rocks& Rocks
Contact (Thermal) Contact (Thermal) Metamorphism:Metamorphism:
Shallow in Crust, dT>dP, Baking near Shallow in Crust, dT>dP, Baking near IntrusionsIntrusions
High Grade RegionalMetamorphism
Convergent Margins
Orogenic Belts:Himalayas, Grenville,
Appalachians
Prograde Metamorphism of Prograde Metamorphism of BasaltBasalt
With Normal Geothermal With Normal Geothermal GradientsGradients
Low Medium High
Upper Limit of Regional Upper Limit of Regional MetamorphismMetamorphism
Migmatites:
Partial MeltingOf Low T°C
Felsic MineralsProduces
Granitic Melt&
ResidualRefractory
Mafic Minerals
Special Low dt/dP Special Low dt/dP Subduction ZoneSubduction Zone
Metamorphism of Basalt & Metamorphism of Basalt & GabbroGabbro
Glaucophane Na-Fe Amphibole Omphacite & Jadeite > 100 km
Dynamic Metamorphism: Dynamic Metamorphism: Strain >>T,PStrain >>T,P
Shear ~1 Earthquake/Shallow Faults Many Quakes/Deep Faults
Breccia Mylonite
Geographic Locations of Geographic Locations of MetamorphicsMetamorphics
Ancient Continental Shields
ConvergentMargins
Sudbury Impact Basin 1.85 Ga, Deformed in Grenville
Ni, Cu, PGEDiscovered
1883
ConstructionOf CPR
Proterozoic Sudbury Impact Basin (1.85 Ga)Cuts Archean Gneisses (2.65 Ga)