Download geol 1030 metamorphic rocks [Compatibility Mode]

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Metamorphic Rocks - Importance
Metamorphic Rocks
1. Provide important information about how changes in
pressure and temperature affect Earth’s crust and
produce economically important materials:
- Formation of mountain ranges, such as the
Appalachians
- Formation of economically important metals,
such as gold, silver and platinum
- Formation of economically important rocks for
construction, such as marble and slate
- Formation of gemstones, such as jade, garnet,
aquamarine, emerald, ruby, and sapphire
Jade
Emerald
Metamorphic Rocks
• Metamorphism
Sapphire
– Involves significant changes in rock:
Aquamarine
Ruby
• Temperature
• Pressure
• Chemical composition
– May result in significant changes in rock:
• Texture
• Mineralogical composition
Metamorphic Grade
Metamorphic Facies
• A group of metamorphic rocks, all of which
formed under similar conditions of
metamorphic grade (i.e., They all formed
under similar conditions of pressure and
temperature.)
• Importance: Enables geologists to
correlate different metamorphic rock types
according to similar conditions of pressure
and temperature.
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Protolith
Changes during Metamorphism
• The ‘parent rock’ which underwent
metamorphism to form a metamorphic
rock.
• Importance: Allows geologists to interpret
the geologic history of metamorphic rocks
prior to the time of metamorphism.
Increase in grain size
Increase in rock density
Development of foliation
Development of new mineral assemblages
stable at the pressures and temperatures
at which metamorphism occurs
Slaty Cleavage
Development of Foliation
Lithostatic
•
•
•
•
Directed
Stress
Stress
(nonfoliated)
(foliated)
Schistosity
Gneissic Banding
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Microphotograph of Foliation
Microphotograph of Foliation
Shear
Directed
Stress
Compressive
Directed
Stress
Shear
Directed
Stress
Compressive
Directed Stress
Types of Metamorphism
• Contact Metamorphism – caused by
heating and/or addition of Si-rich fluids to
the ‘country rock’ surrounding a mass of
magma. Forms a zone of metamorphism
around the magma (contact aureole,
contact halo).
Contact Metamorphism
Contact
Aureole
– Typically non-foliated due to lack of directed
stress
Contact Metamorphism
Types of Metamorphism
• Burial Metamorphism – caused by deep
burial of sedimentary rocks.
– Weakly foliated or non-foliated
• Regional (Dynamothermal) Metamorphism
Caused by intense stress in the crust over
large geographic regions
– Usually related to plate tectonic activity (e.g.,
continental collisions)
– Strongly foliated
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Burial Metamorphism
Regional Metamorphism
Weak foliation in anthracite
due to deep burial
Regional Metamorphism
Types of Metamorphism
• Hydrothermal Metamorphism
(Metasomatism) – caused by chemical
reactions between dissolved ions in hot
groundwater and the rock through which it
flows
– Results in formation of hydrothermal ore deposits
(gold, silver, copper, lead, zinc, galena)
Hydrothermal Metamorphism
Foliated Metamorphic Rocks
• Most characteristic of regional
metamorphism
• In order of increasing metamorphic grade:
– Slate
– Phyllite
– Schist
– Gneiss
– Migmatite
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Slate
Slate Microphotograph
Phylite
Phyllite Microphotograph
Schist
Schist Microphotograph
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Gneiss
Gneiss Microphotograph
Migmatite
Non-foliated Metamorphic Rocks
• Marble
– Protolith = limestone
• Quartzite
– Protolith = quartz-rich sandstone
• Hornfels - contact metamorphism
Granoblastic texture = equigranular crystals
White rock = crystallized melt
Dark rock = ‘residue’ of partially melted protolith
Marble
Microphotograph of Marble
granoblastic texture
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Quartzite
Microphotograph of Quartzite
granoblastic texture
Hornfels
Microphotograph of Hornfels
granoblastic texture
North Carolina Metamorphic Minerals
The Blue Ridge and Piedmont geologic provinces of North Carolina are home
to some of the most important gemstone collecting localities in North America
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Sapphire – Haywood County
Gold
Emerald – Alexander County
North Carolina’s MOST important gem!
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