CHAPTER 8 GEO

. Rank the following metamorphic rocks in order of increasing grade of metamorphism: schist, granulite, phyllite, slate, gneiss.

. Slate: Low grade metamorphism, Phyllite: upper lower grade metamorphism Schist: upper low to medium grade metamorphism, Gneiss: high grade metamorphism, Granulite: high to very high grade metamorphism

Identify the parent rock for each of the following metamorphic rocks: slate, quartzite, marble, greenstone, and anthracite

. slate-shale quartize-sandstone marble-limestone greenstone-basalt anthracite-bituminous coal

In what tectonic environment do blueschists and eclogites form?

Blueschist Facies (very high pressures, relatively low temperatures) Occurs within subduction zones Metamorphosed basalt and shale contain blue amphiboles Eclogite facies (extremely high pressures,moderate-high temperatures)

What are the differences between burial and regional metamorphism? Which is more extensive? Where does each type occur? Describe the stresses associated with burial versus regional metamorphism.

Burial Metamorphism • Sedimentary rocks that had undergone diagenesis are buried even deeper • A relatively mild type of metamorphism • Diagenesis grades into burial metamorphism • Results in partial alteration of mineralogy and texture • Original bedding and sedimentary structures usually preserved Regional Metamorphism (Figure 8.22) • When temperatures & pressures increase beyond range of burial metamorphism • Takes place under high temperatures & pressures over large areas • Intense alteration of rock mineralogy and texture • Original sedimentary structures destroyed • Caused by major tectonic forces

Describe how foliation is produced in a metamorphic rock (3 mechanisms). Name two common platy minerals that produce foliation in metamorphic rocks. Can non-platy minerals exhibit foliation (think metaconglomerate)

Foliation: any planar arrangement of mineral grains or structural features within a rock. Examples of foliation: - parallel alignment of platy minerals like chlorite and micas - parallel alignment of flattened mineral grains and pebbles - compositional banding - Slaty cleavage where rocks can be easily split into thin, tabular sheets Can form in 3 ways: - rotation of platy and/or elongated minerals - recrystallization of minerals in the direction of preferred orientation - changing the shape of equdimensional grains into elongated shapes that are aligned

What are the agents of metamorphism?

Heat, Pressure(stress),Chemically active fluids.

Know how the different types of metamorphism are related to plate tectonics (see Fig. 8.29 in your textbook). In terms of tectonic environments, where would you find each of the following metamorphic conditions: high-temperature/low-pressure, high-temperature/high-pressure, low-temperature/high-pressure, and hydrothermal metamorphism.

High Temp/Low p- Earth crust need magma chamber Aruelo High tem/high p- Buried deep Hydrothermal- Mid-Ocean ridge

Describe contact metamorphism. Where does it occur? What type of geothermal gradient is associated with contact metamorphism? What is a contact metamorphic aureole?

Occurs at high temperatures Restricted to a small area around the margins of a magmatic intrusion Geothermal gradients are high - Found near the surface of earth - rocks are subjected to heat when they are intruded by magma. - Adjacent "host" rock is baked by the magma underneath - subjected to high temps when in sub ducting zone - pressure and temperature increase with depth

Where does hydrothermal metamorphism occur?

along mid ocean ridges where two plates spread apart,

What are index minerals? How are index minerals used in mapping metamorphic terrain?

degree of metamorphism a rock has experienced

What is the difference between differential stress and confining pressure? Which of these two stresses is most likely to produce foliation in a metamorphic rock?

differential stress, stresses on the sides are greater. Stresses are the same on all sides for confining pressure.

Describe hydrothermal metamorphism. What types of reactions occur? Where does hydrothermal metamorphism occur? What metamorphic rock is a typical product of hydrothermal metamorphism?

reactions between rocks and warm fluids

What are migmatites? How do migmatites form? Do they represent low or high temperatures?

temperatures Migmatite is a rock at the frontier between igneous and metamorphic rocks. Migmatites form under extreme temperature conditions during prograde metamorphism, where partial melting occurs in pre-existing rocks. Metamorphism reaches a temperature >700 degrees C where rocks begin to melt- felsic minerals preferentially melt - mafic minerals remain solid - resulting silica rich liquid invades partially melted rock as veins and stringers softened rock contorts and deforms under differential stress

What is cataclastic metamorphism? Where does it occur? What is the difference between a fault breccia and mylonite?

• Results from the crushing and shearing of rock during tectonic movement • Generally localized along fault planes • Might produce sheared, highly deformed rocks called mylonites