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Factors in Metamorphism Metamorphism is effected by four main factors: Fluids Fluids Temperature Temperature Pressure Pressure Deviatoric stress Deviatoric.

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Presentation on theme: "Factors in Metamorphism Metamorphism is effected by four main factors: Fluids Fluids Temperature Temperature Pressure Pressure Deviatoric stress Deviatoric."— Presentation transcript:

1 Factors in Metamorphism Metamorphism is effected by four main factors: Fluids Fluids Temperature Temperature Pressure Pressure Deviatoric stress Deviatoric stress

2 Factors in Metamorphism Pressure A uniform compressive stress created by Load (weight of overlying rocks) Load (weight of overlying rocks) Fluid pressure Fluid pressure Increases greatly deeper in the crust. temperature With temperature, controls what minerals are stable.

3 Factors in Metamorphism Regional Metamorphism: Stress imbalance causes compression in some directions and expansion in others. Controls: Foliation Foliation (orientation of minerals into layers) Need to have either platey (micas) or elongate (hornblende) minerals Non-Foliated rocks, with no platey or elongated minerals (quartz, feldspar, calcite, dolomite, etc.) Deviatoric / Differential Stress

4 Deviatoric Stress Hydrostatic Pressure Hydrostatic Pressure vs Deviatoric Stress

5 Deviatoric Stress Foliation Foliation - alignment of minerals (platey or elongated minerals) Slate Slate – Alignment of fine grained minerals (dull) Phyllite Phyllite – Alignment of fine grained minerals (sheen, wavy texture, still too small to see individual grains) Schist Schist – Alignment of fine to coarse grained minerals Gneiss Gneiss – Alignment of medium to coarse grained minerals, and segregation of different minerals into light and dark bands Deviatoric stress is the primary control on foliation

6 Foliation

7 Slate slaty cleavage. Protolith– fine grained rock like shale, mudstone, or siltstone Foliation - Slaty Cleavage

8 Arizona State University Gneiss shows gneissic banding Foliation - Gneissic Banding

9 Metamorphic rock with aligned flat minerals Low GradeHigh GradeSchistSchistSlateSlateGneissGneiss

10 Metamorphic Grade Index Mineral Index Mineral – a mineral in a metamorphic rock which indicates a certain metamorphic grade Isograd Isograd – line marking the first appearance of an index mineral on a map or cross-section Index Mineral Index Mineral – a mineral in a metamorphic rock which indicates a certain metamorphic grade Isograd Isograd – line marking the first appearance of an index mineral on a map or cross-section

11 Metamorphic rock without minerals that can be foliated (or from contact metamorphism) Protolith Mineralogy limestone carbonates quartz sandstone quartz coal none mafic rocks Amphiboles (i.e. hornblende)


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