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Metamorphic Rocks

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by

Gary McClure

on 20 January 2016

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Transcript of Metamorphic Rocks

Meatmorphic rocks form when existing rocks are changed by heat & pressure.
Metamorphic Rocks
Formation of Metamorphic Rocks
Metamorphism means to change form
Most

metamorphic changes occur at elevated temperatures & pressures.
metamorphism occurs in one of two settings:
Contact metamorphism
Regional metamorphism
Contact Metamorphism
During contact metamorphism, hot magma moves into rock
Usually produces minor changes, low-grade metamorphism
marble is an example, forms
when magma intrudes limestone
Regional Metamorphism
During mountain building, large areas of rock are subjected to extreme pressures & temperatures
Regional metamorphism results in large-scale deformation and high-grade metamorphism
Agents of Metamorphism
Heat
pressure
hydrothermal solutions
a rock can experience all three at the same time
HEAT
The most important agent of metamorphism
provides the energy to drive chemical reactions
some chemical reactions cause existing minerals to recrystallize
Other reactions cause new minerals to form
The heat for metamorphism comes from two sources- magma and the change in temperature with depth.
Magma essentially "bakes" any rocks that are in contact with it.
Pressure (stress)
Pressure also increases with depth
Pressure is applied in all direction on rocks, much like water.
Pressure on rocks causes the spaces in between mineral grains to close. Giving more compaction and greater density.
This pressure may cause minerals to recrystallize into new minerals
Increases in temperature & pressure causes rocks to flow rather than fracture. Under these conditions, mineral grains tend to flatten and elongate.
Reactions in Solution
When hot, water based solutions escape from a mass of magma, they are called hydrothermal solutions
These hot fluids also promote recrystallization by dissolving original minerals and then depositing new ones.
Classification of Metamorphic Rocks
The texture of metamorphic rocks can be
Foliated
Nonfoliated
Foliated
When rocks undergo contact metamorphism, they become more compact & thus more dense
some minerals recrystallize with a preferred orientation, which is at right angles to the direction of the force. The resulting alignment usually gives the rock a layered or banded appearance. This rock is called
a foliated rock.
Nonfoliated
A metamorphic rock that does not have a banded texture is called a
nonfoliated metamorphic rock
.
Most nonfoliated rocks contain only one mineral.
example: Marble
Summary
metamorphic rocks are formed when prexisting rocks are changed by heat, pressure, or hydrothermal solutions
contact metamorphism is caused when hot magma intrudes a body of rock. minor changes.
Classified by texture - foliated & nonfoliated
Regional metamorphism is associated with mountain building, can be extreme.
Review
compare & contrast contact and regional metamorphism
contact metamorphism is the result of rock in contact with magma causing minor changes, regional metamorphism is associated with mountain building causing high-grade changes.
Name the agents of metamorphism and explain how each changes a rock.
heat causes existing minerals to recrystallize or new ones to form, Pressure produces more compact and dense rock, Fluids aid in recrystallization by dissolving original minerals and depositing new ones.
What are foliated rocks, and how do they form?
How are metamorphic rocks classified?
Foliated rocks are banded rocks that form when minerals realign as the result of pressure from opposing sides .
Metamorphic rocks can be classified according to composition and texture.
Full transcript