Lecture 15
Created
@March 9, 2022 11:56 AM
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Geology 101
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I Property 1
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Finishing up Metamorphism today
Review
Causes for Metamorphism:
Heat, Temperature, Lots of Time
Isochemical = same chemical composition
Dewatering = loss of water in chemical composition
Where does metamorphism take place??
At great depths
o With increasing depth into the earth, pressure increases and so does temperature (25 C per Km)
At convergent plate boundaries
o Continent collisions and even subduction zones are areas of intense pressure and heat, as plates are colliding
: Near igneous intrusions
o Near magma bodies, temperatures are very high, this is enough to cause metamorphism in some instances
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How does metamorphism occur? Around 2o0 'c
1. When rocks are buried
a. The deeper rocks are, the more pressure they are under
b. Recall the geothermal gradient, deeper also means hotter
2. Through tectonic stress
a. Continent collision and subduction leads to burial and compression of rocks
b. Because this type of metamorphism tends to occur over huge areas, it is referred to as "REGIONAL METAMORPHISM"
i. Such as the Himalayas, with the roots of the mountains made of high-grade metamorphic rock
Involves structural changes, like breaking and bending
The Metamorphic Continuum
Increasing heat and pressure Increasing metamorphism
imentary rock
Shale
Slate
Phylite
Schist
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Image by Karin Kirk for MIA+BSI
Metamorphic rocks are in high abundance around the Rocky Mountains, where a series
of plate collisions caused regional metamorphism.
In Washington, they are found in the Northern/Northeastern part of the state.
Rocks get meated but not melted by magma
Referred to as contact metamorphism
o Because it gets less hot as you move away from the magma chamber, the metamorphic rocks tend to be zoned, further and further away gets less
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2
metamorphosed
Rocks, Minerals, Composition
Mineral
Needs to be: Naturally occurring, solid, inorganic, have a definite chemical composition and a crystalline lattice
Composition
Quartz: always SiO2, Halite: always NaCl, Olivine: uses either (Mg,Fe)2 in conjunction with SiO4
IRON is the most abundant element on the whole earth
Rocks: Aggregates of minerals
Composition
o Chemical composition
o Mineral Assemblage
Texture
o Size and shape of mineral grains
Fabric (foliation)
o Alignment/ connections of mineral grains
Types of Rocks
Igneous
1) Volcanic (Extrusive), above the earth's surface
2) Plutonic (intrusive), below the earth's surface
Sedimentary Rocks
1) Clastic
2) Biogenic
3) Chemical precipitation
Lecture