Like sliding out a deck of cards Compression and Shear Compression and shear

Like sliding out a deck of cards compression and

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Like sliding out a deck of cards Compression and Shear - Compression and shear applied together causes mineral grains to change shape - Equant - roughly equal in all dimensions - Inequant - dimensions not the same - Platy (pancake-like) - one dimension shorter
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- Elongate (cigar-shapped) - one dimension longer - Preferred orientation of inequant minerals is a common feature of metamorphic rocks. Development of Preferred Orientation - Compression and shear combine with elevated T and P. - Cause rocks to change shape without breaking - Internal texture of deforming rocks can also change - Minerals rotate into preffered orientations - Minerals grow in preferred directions relative to streching Hydrothermal Fluid Metamorphism - Hot water with dissolved ions and volatiles - Hydrothermal fluids facilitate metamorphism - Accelerate chemical reactions - Alter rocks by adding or subtracting elements - Hydrothermal alteration is called metasomatism - It is often associated with mineralization of ore deposits - On ore genesis Types of Metamorphic Rocks - Two major subdivisions - foliated and nonfoliated - Foliation - parallel surfaces or layers in metamorphic rocks - Alignment of inequant grains or compositional banding - Classified by composition, grain size, and foliation type - Two major subdivisions of metamorphic rocks - Nonfoliated - no planar fabric evident - Minerals recrystallized without compression or shear - Comprised of equant minerals only - Classified by mineral composition Foliated metamorphic rocks - Slate - fine-grained, low grade metamorphic shale - Has a distinct foliation called slaty cleavage - Develops by parallel alignment of platy clay minerals - Slaty cleavage develops perpendicular to compression - Slate breaks along foliation creating sheets used for roofing - Phyllite - fine-grained mica-rich rock - Formed metamorphism of slate - Clay minerals neo crystallize into tiny micas - Has silky sheen called phyllitic luster - Phyllite is between slate and schist - Metaconglomerate - metamorphosed conglomerate - Pebbles and cobbles are flattened by:
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- Pressure solution - Plastic deformation - Foliation is defined by the flattened clasts - Schist - fine to coarse rock with larger micas - Forms at higher temperature than does phyllite - Has a distinct foliation from large micas called schistosity - Schist has abundant large micas - biotite and muscovite - Gneiss - distinct compositional bands, often contorted - Light bands of felsic minerals ( quartz and feldspars) - Dark bands of mafic minerals (biotite or amphibole) // Nuvvuagittuq Faux Amphibolites - The source magma that formed this metamorphic rock has been age-dated to 4.28Ga.
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  • Fall '09
  • Metamorphic rocks

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