Metamorphic Rocks (L9) Flashcards
What does metamorphism mean and involve
meta means change and morph means form so it involves a change in form, converting it from one rock type to another
What are the main agents of change?
heat, pressure, and chemically active fluids
What are the 3 main types of metamorphism?
contact metamorphism - involves heat, uniform pressure
regional metamorphism - involves heat, differential pressure
Metasomatism - involves reaction of minerals with active fluids during the process
When does contact metamorphism commonly occur?
when a pre-existing rock is heated by magma of an igneous intrusion, forming a metamorphic halo, or “aureloe” in the adjecent country rock
When does Regional Metamorphism commonly occur?
occurs when a pre-existing rock is heated (baked) under unequal pressure (differential stress)
in terms of texture, what are the main diff between contact and regional metamorphism?
the orientation of flat and platy or elongates minerals
In contact metamorphism, pressure is ____ and retains a ___
uniform (in all direction) and retains a random orientation
In which areas do regional metamorphism generally occur in?
areas where 2 lithospheric plates are pressing against one another, and rocks are subjected to differential stress (pressure applied unevenly)
How is foliation and bedding different?
foliation is a uniquely metamorphic characteristic, produced by the preferred alignment of platy/elongate minerals while bedding is a sedimentary characteristic
Rocks containing platy/elongate minerals that are subjected to regional metamorphism are ____
typically foliated
with increasing metamorphism, shale changes:
to slate, to phylite, to schist, and finally to gneiss
What is shale?
a sedimentary rock made of microscopic grains of clay and quartz
Why is shale called a parent rock?
because it is the rock we start off with
Shale’s property is?
very dull and breaks into layers
What do clay minerals from shale begin to transform into next and what is its foliation type called?
transforms into small, platy mica crystals that form slate
called Slaty Cleavage