meta rocks GEO 2

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meta rocks GEO 2
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2010-06-20 23:27:18
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meta rocks GEO
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meta rocks GEO 2
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  1. Metamorphic Change Form
    • A. Preexisting igneous, sed, meta rocks altered in solid state through heat , pressure, chemically active fluids.
    • B. Metamorphic change occurs bc minerals in a preexisting rock are out of equilibrium when exposed to new conditions.
    • C. Changes may occur
    • 1.Minerals may become aligned (foliated texture)
    • 2.Minerals may grow larger.
    • 3.New minerals may form
    • D.Metamorphic grade.
    • 1. Low-grade metamorphism
    • a.Occurs at low temperatures, low pressure
    • 2.High grade metamorphism
    • a. Occurs at high temperatures, high pressures.
    • E. Metamorphic Settings
    • 1. Contact metamorphism
    • a. Preexisting rocks are affeected by the heat from nearby magmas
    • 2.Regional metamorphism
    • a. Occurs during mountain building at plate boundaries
    • i. Rocks affected by high temperatures and pressures
    • b. Usually affects a large area
  2. Agents of Metamorphism
    • A. HEAT
    • 1. Prvides energy to drive chemical reactions
    • 2.Sources of heat
    • a. Geothermal gradient
    • i. Increasin temperature with increasin depth in Earth
    • b. Nearby magma
    • i. Limestone may be altered to marble
    • B. PRESSURE
    • 1. Confining pressure (lithostatic pressure)
    • a. Pressure is the same in all directions
    • b. Minerals may recrystallize as smaller, denser minerals
    • 2. Directed Stress
    • a. Stress is greater in on e direction
    • b. Causes foliation (alignment of minerals)
    • c.Occurs at convergent plate boundaries
    • C. CHEMICALLY ACTIVE FLUIDS
    • 1. hot water with ions
    • 2. New minerals may form
  3. Classification of Metamorphic Rocks
    • A. FOLIATED METAMORPHIC ROCKS
    • 1. Exhibit an alignement of minerals
    • 2. Usually form during regional metamorphism
    • B. METAMORPHIC ROCKS WITH FOLIATED TEXTURES
    • 1. State
    • a. Fine grained
    • b. Slaty cleavage
    • i. Splits along flat
    • ii. Reflects alignment of clay sized min
    • c. Slate forms through the low grade metamorphism of shale
    • 2. Schist
    • a. Coarse grained rocks composed of LESS THAN 50 percent platy minerals
    • b. Wavy foliation
    • c. Intermediate to high grade metamorphism
    • 3.Gneiss
    • a. Distinctive light and dark bands
    • b. Coarse grained
    • c. High gade metamorphism
    • C. NONFOLIATED METAMORPHIC ROCKS
    • 1. Lack of platy minerals
    • 2. Rocks are often composed one primary mineral
    • D. METAMORPHIC ROCKS WITH NONFOLIATED TEXTURES
    • 1. Ouartzite
    • a. composed of quartz grains
    • b. Parent rock-quartz sandstone
    • i. Quartz grains have been fused together
    • c.Grainy texture
    • d. May form during regional or contact metamorphism
    • 2. Marble
    • a. composed primarily of calcite grains
    • b. Parent rock-limestone
    • i. Calcite grains recrystallize and grow larger
    • c. Coarsely cyrstalline
    • d. May form during regional or contact metamorphism
    • 3. Anthracite coal
    • a. Hard , black coal
    • b. Parent rock-bituminous coal

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