Geology 101 Quiz 8 Flashcards
metamorphic rocks definition
rocks that have been altered in composition or texture by heat or pressure
high-grade rocks form at
high temperature and/or pressure
low-grade rocks form at
lower temperature and/or pressure
if the temperature rises still higher,
the rock melts
regional metamorphism
occurs over a very large area
regional metamorphism is typically associated with
convergent plate boundaries
examples of regional metamorphism
subduction zones (high temp from friction) and continental collisions (high pressures from colliding plates)
contact metamorphism
high temperature metamorphism where magma heats up but does not melt adjacent rock
aureole
the halo of altered rock around the igneous intrusion formed by metamorphism
right next to the igneous intrusion will typically be
high grade metamorphic rock
rock farther away from the igneous intrusion that heats up will be
lower grade
cataclastic metamorphism
crushing and smearing of rock along fault zones
examples of cataclastic metamorphism
subduction zones, transform fault boundaries
hydrothermal metamorphism
metamorphism caused by interaction with hot water (usually involves exchange of some ions)
examples of hydrothermal metamorphism
mid-ocean ridges (Mid-Atlantic Ridge, East Pacific Rise)
what happens during hydrothermal metamorphism?
water in the pores in the ridge gets heated, the hot water thermally alters the rock and dissolves some of the minerals, the heated water is less dense and rises
when the hot water hits the cooler ocean water, some of the dissolved minerals precipitate (creates “black smokers”), cooler seawater enters from the sides to replace the rising hot water, continuing the cycle
burial metamorphism
heat and pressure caused by deep burial
example of burial metamorphism
sedimentary basins
what do sedimentary basins do?
collect eroded sediment from nearby mountains - as the sediment layers accumulate, the weight causes the crust to sink deeper in the mantle; over time, deposits can become buried under thousands of feet of sediment
the earth gets ? with depth by how much
hotter; about 30*C per km
shock metamorphism
caused by large meteorite impact
example of shock metamorphism
Meteor Crater, Arizona
at low temperature and high pressure, expect
cataclastic and regional metamorphism
at localized high temperature and pressure, expect
impact metamorphism
at intermediate temperature and pressure, expect
burial metamorphism
at high temperature and low pressure, expect
contact and hydrothermal metamorphism
metamorphism can produce both ? and ? alterations
mineral and textural
mineral alteration is achieved by
changing either the arrangement of atoms, or swapping some atoms for others
structural alteration
the chemical formula is the same, but the arrangement of atoms changes (usually more compact arrangement due to high pressure)
graphite turned to diamond is an example of
structural alteration (both are pure C, but the C atoms in diamond are much more closely arranged)
element substitution
one atom is exchanged for another resulting in a new mineral
exchange an Fe atom for a Mg atom is an example of
element substitution
textural alteration is caused by
either recrystallizing or by stretching or smearing
recrystallize
under high temperature and pressure, atoms within minerals can migrate to make larger crystals, or crystals oriented due to high differential pressures (i.e. more pressure in one direction)
when the pressure is the same in all directions, crystals will have a(n) ? alignment
random
if the pressure is greater in one direction (like from two plates colliding), crystals tend to align ? to the greater force
perpendicular
if differential pressure results in movement, minerals may be
smeared, stretched, or folded