Chapter 7 Flashcards
metamorphism
processes of change that a rock undergoes when exposed to physical and chemical conditions significantly different from those that it formed from
metamorphic rock
end product of a rock that undergoes metamorphism
protholith
parent rock
texture of the protholith may change due to:
Recrystallization (when small grains of a mineral coalesce to form larger grains)
Pressure solution (if water is present, some minerals dissolve and the dissolved ions re-precipitate changing relationship between grains)
Alignment of grains (the result is foliation and lineation)
mineralogy of the protholith may change by
phase change: one polymorph changes to another more stable at the new conditions {there is no change in the chemical composition}
Neocrystallization: process of chemical reactions between protholith minerals during which ions from two or more minerals combine to create new minerals
diffusion
As temperatures rise, atoms vibrate more rapidly, and chemical bonds holding the atoms into the lattice of minerals begin to stretch and break, the freed atoms migrate slowly through the solid rock
Lithostatic pressure
results from the burial within the Earth and in all equal directions
lots of pressure at great depths
phase change
a new mineral with a more compact atomic arrangement can form that is more stable under the high-pressure conditions
polymorphs
minerals like diamond and graphite that have identical compositions but different internal structures
directed pressure
also called differential stress
type of pressure in a rock due to vise-like squeezing and or shear
phase diagram
has pressure and depth on the vertical axis and temperature on the horizontal axis
hydrothermal fluids
rocks that contain high-temperature liquids, gases, and ions of other elements have been dissolved
May be released from magma when the magma solidifies
metasomatism
when the chemical composition of a metamorphic rock changes significantly due to reaction with hydrothermal fluids
Contact metamorphism
occurs where rocks are subjected to elevated heat without a change in pressure and without the application of differential stress
happens when an igneous intrusion comes in contact with a rock
Regional metamorphism
occurs where rocks in a large region of crust are subjected to increases in temperature and pressure and differential stress
happens during mountain building
Burial Metamorphism
happens when rocks are simply buries very deeply by overlying sediment
Dynamic metamorphism
rock undergoes differential stress in response to shear along a fault zone but does not undergo a change in temp or lithostatic pressure
Shock metamorphism
where a meteorite hits the Earth
enormous kinetic energy is converted to heat and differential stress
Metasomatism
where hydrothermal fluids are present
Classes of metamorphic rock
Aluminous Quartzo-Feldspithic Calcareous Mafic Organic
preferred orientation
foliation and lineation
foliation
if it contains a stack or parallel feature alternating bands of different material
lineation
rod shaped minerals are aligned parallel to one another
Slate
low grade metamorphosed shale or mudstone
phyllite
a grade higher than slates
schist
medium to high grade rock with a strong folitation
Gneiss
high grade metamorphic rock of any composition minerals segregate into light and dark layers
Anthracite coal
black shiny hard rock made of carbon that has no visible mineral grains and low specific gravity
metamorphic grade
a broad, informal approximation of how much a rock has changed
grain size
increases with increasing metamorphic grade
porphyroblasts
minerals grow much larger than others in the rock
the larger the mineral the higher the metamorphic grade and the longer the rock stayed at its peak metamorphic temperature
gnessic banding
compositional banding defined by alternating light and dark colored layers
porphyroclasts
leftover grains of feldspar after the surrounding rock has changed into a mass of fine mica
metamorphic index minerals
minerals that therefor indicate the conditions of metamorphism
