GEO 303 Chapter Notes - Chapter 9: Gneiss, Mica, Muscovite

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10 May 2016
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Geo Chapter 9 Notes:
Intro
oMetamorphism: to transform
A rock that was once sedimentary or igneous that has
transformed significantly enough to justify calling it a new rock
High pressure and high temperature are the factors that
warrant a rock being metamorphic
Sheer stress: force that is applied to the rock along certain
directions only
Role of Water in Metamorphism
oDuring metamorphism, water is dissolved within the rock
Types of Metamorphism
oDynamic metamorphism: rocks on either side are forced past one
another for great distances, they are crushed and smeared
oContact metamorphism: seen along the margins of some igneous
intrusions, heat and fluid (mostly H20) escaping from the hot magma
can penetrate the surrounding, or host rock
High temperature is the chief ingredient
oRegional metamorphism: sheer stress, high pressure, and high
temperature are all likely to be important here
Affects a very large areas in which rocks that formed near the
surface have been brought down to great depth where they
recrystallize, attaining equilibrium with the condition of the
new environment
Common Metamorphic rocks
oSlate: tiny parallel wisps of muscovite mica appear, which enables the
rock to split into thin, flat sided plates characteristic of slate
oMetamorphic foliation: the theme of parallel layering of crystal faces
is carried out in most metamorphic rocks
oSchist: coarse grained rock
oSchist and gneiss are convenient terms to describe appearance
without regard to origin
Ancient Regional Metamorphism: A classic study
oIsograds: mark zones of equal grade or intensity of metamorphism
Summary
oMetamorphic rocks originate when igneous, sedimentary, or
preexisting Metamorphic rocks are recrystallized in the sold state,
transformed into a new set of minerals which are stable under
conditions of elevated temperature and pressure
oSheer stress and traces of H20 increase the rate and degree of
metamorphism
oRegional metamorphism affects rocks that formed near the surface,
brought to great depth in the earth
o
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