Summa 2 Flashcards
Changes rock via temperatures and/or pressures unlike those in which it initially formed
metamorphism
All metamorphic rocks have a _______ (the rock from which it formed)
parent rock
the rock from which it formed
parent rock
______________ can be igneous, sedimentary, or other metamorphic rocks.
Parent rocks
Change occurring during metamorphism
metamorphic grade
Progresses from low grade (low temperatures and pressures) to high grade (high temperatures and pressures)
metamorphic grade
low temperatures and pressures
low grade
high temperatures and pressures
high grade
During metamorphism, the rock must remain essentially _____
solid
the different drivers of metamorphism
heat, confining pressure, differential and compressional stress, chemically-active fluids
Most important agent
heat
two sources of heat
geothermal heat and contact metamorphism
an increase in temperature with depth (about 25o C per kilometer)
geothermal gradient
rising mantle plumes
contact metamorphism
Forces are unequal in different directions
differential stress
Causes the spaces between mineral grains to close
confining pressure
Forces are applied equally in all directions
confining pressure
Rocks are squeezed as if in a vice
Shortened in one direction and elongated in the other direction
compressional stress
Enhances migration of ions
chemically-active fluids
Aids in recrystallization of existing minerals`
chemically-active fluids
metamorphic textures
foliated, non-foliated, porphyroblastic
Rock or slaty cleavage
foliated
Split into thin slabs
foliated
Low-grade metamorphism
foliated
Platy minerals (mica) are visible
Schistosity
Exhibit a planar or layered structure
schistosity
Rocks having this texture are referred to as schist
schistosity
some textures of foliated
schistosity, gneissic,
High-grade metamorphism, segregation of minerals into light and dark bands
gneissic texture
Metamorphic rocks with this texture are called gneiss
gneissic texture
Gneiss does not ____ as easily as slates and schists
split
______ composed of minerals that lack layering/foliation
Nonfoliated
Large grains (porphyroblasts) surrounded by a fine-grained matrix of other minerals
porphyroblastic
examples of foliated rocks
slate, phyllite, schist, gneiss
example of non-foliated rocks
marble, quartzrite
-Very fine-grained
-Excellent rock cleavage
-Most often generated from low-grade metamorphism of shale, mudstone, or siltstone
slate
-Degree of metamorphism between slate and schist
–Platy minerals are larger than slate but not large enough to see with the unaided eye
-Glossy sheen and wavy surfaces
-Exhibits rock cleavage
phyllite
- Medium- to coarse-grained
-The parent rock is shale that has undergone medium- to high-grade metamorphism
-The term schist describes the texture
-Platy minerals (mainly micas) predominate
-Can also contain porphyroblasts
schist
-Medium- to coarse-grained metamorphic rock with a banded appearance
-The result of high-grade metamorphism
-Composed of light-colored, feldspar-rich layers with bands of dark ferromagnesian minerals
gneiss
-Crystalline rock from limestone or dolostone parent rock
-The main mineral is calcite
-Calcite is relatively soft (3 on the Mohs scale)
-Used as a decorative and monument stone
-Impurities in the parent rocks provide a variety of colors
marble
- Formed from a parent rock of quartz-rich sandstone
- Quartz grains are fused together
- Pure _____ is white
Iron oxide may produce reddish or pink stains
Dark minerals may produce green or gray stains
quartzite
quart sandstone will undergo metamorphism under increase in temperature and pressure to form?
quartzite
shale
very fine-grained
slate
fine-grade
schist
medium to coarsed-grained
gneiss
coarse-grained
parent rock of slate
shale, mudstone, or siltstone
parent rock of phylllite
shale, mudstone, or siltstone
parent rock of schist
shale, mudstone, or siltstone
parent rock of gneiss
shale, granite, or volcanic rocks
parent rock of marble
limestone, dolostone
parent rock of quartzite
quartz sandstone
parent rock of hornfels
often shale, but can have many composition
If the sedimentary rock limestone or dolomite is metamorphosed it can become the metamorphic rock ____.
marble
If the sedimentary rock sandstone is metamorphosed it can become the metamorphic rock ____.
quartzite
If the sedimentary rock shale is metamorphosed it can become the
metamorphic rock ___.
slate
If the metamorphic rock slate is metamorphosed it can become the metamorphic rock ____
phyllite
If the metamorphic rock phyllite is metamorphosed it can become the metamorphic rock ____.
schist
If the metamorphic rock schist is metamorphosed it can become the metamorphic rock ___.
gneiss
metamorphic environments
-contact or thermal metamorphism
-burial metamorphism
-subduction zone metamorphism
-regional metamorphism
-impact metamorphism
Results from a rise in temperature when magma invades a host rock
contact or thermal metamorphism
Occurs in the upper crust (low pressure, high temperature)
contact or thermal metamorphism
The zone of alteration (aureole) forms in the rock surrounding the magma
contact or thermal metamorphism
The zone of alteration (______) forms in the rock surrounding the magma
aureole
Associated with very thick sedimentary strata in a subsiding basin
Gulf of Mexico is an example
burial metamorphism
Sediments and oceanic crust are subducted fast enough that pressure increases before temperature
subduction zone metamorphism
Creates the most metamorphic rock
regional metamorphism
Associated with mountain building and the collision of continental blocks
regional metamorphism
Occurs when meteorites strike Earth’s surface
impact metamorphism
Product of these impacts are fused fragmented rock plus glass-rich ejecta that resemble volcanic bombs
impact metamorphism
Product of these impacts are fused fragmented rock plus glass-rich ejecta that resemble volcanic bombs that are called
impactiles
______ (de = out, forma = form) is a
general term that refers to the changes in
the shape or position of a rock body in
response to differential stress.
Deformation
de
out
forma
form
Most crustal deformation occurs along
__________. Plate motions and the
interactions along plate margins generate
the __________ that cause rock to
deform.
plate boundaries; tectonic forces
The basic geologic features that form as a
result of the forces generated by the
interactions of tectonic plates are called
___________
rock structures, or geologic structures
the different rock structures
folds, faults, joints
____(wave like undulations)
folds
____ (fractures along which one rock
body slides past another)
faults
cracks
joints
The Force That Deforms
Rocks
stress
3 types of stress
compressional, tensional, shear
Differential stress that squeezes a rock mass as if placed in a vise is known as ________ stress
compressional
(com =____, premere = _____).
together; to press
Compressional stresses are most often associated with _____ plate boundaries.
convergent
When plates ____, Earth’s crust is generally _______ and ______.
collide; shortened horizontally; thickened vertically
Over millions of years, this _____ produces ________.
deformation; mountainous terrains
Mountains that are formed by ____ stresses are called ____ mountains.
compressional; folded
Differential stress that pulls apart or elongates rock bodies is known as ______ stress
tensional
tendere=
to stretch
Along _____ plate boundaries where plates are moving apart, ______ stresses stretch and lengthen rock bodies.
divergent ; tensional
For example, in the Basin and Range Province in the western United States, _____ forces have ______ and _______ the crust to as much as twice its original width.
tensional; fractured; stretched
Differential stress can also cause rock to shear, which involves the movement of one part of a rock body past another.
shear stress
_____ is similar to the slippage that occurs between individual playing cards when the top of the deck is moved relative to
the bottom.
Shear
Small-scale deformation of rocks by __________ occurs along closely spaced parallel surfaces of weakness, such as foliation surfaces and microscopic fractures, where slippage changes the shape of rocks.
shear stresses
By contrast, at transform fault boundaries, such as the San Andreas Fault , _______ causes large segments of Earth’s _____to slip horizontally past one another.
shear stress; crust
It extends roughly _______ kilometers through California,
USA . It forms the tectonic boundary between the Pacific
Plate and the North American Plate.
1,200
A Change in Shape Caused by Stress
strain
Differential stresses can also change the shape of a rock body, referred to as _____
strain
____ is the force that acts to deform rock bodies, while ______ is the resulting deformation (distortion), or change in the shape of the rock body.
Stress; strain
When rocks are subjected to _____ that exceed their strength, they deform, usually by bending or breaking.
stresses
When rocks are subjected to stresses that exceed their strength, they deform, usually by _________
bending or breaking.
types of deformation
elastic, brittle, ductile
When stress is applied gradually, rocks initially respond by deforming ______.
elastically
Changes that result from elastic deformation are _____; that is, like a rubber band, the rock will snap back to nearly its original size and shape when the stress is _____.
recoverable; removed
During elastic deformation, the chemical bonds of the
minerals within a rock are _____ but do not ___.
stretched; break
When the stress is ____, the bonds snap back to
their _____ length.
removed; original
______ deformation occurs when stress breaks
the chemical bonds that hold a material together.
Brittle
When the elastic limit (strength) of a rock is ____, the rock either _____.
surpassed; bends or breaks
Rocks that break into smaller pieces exhibit ____ deformation (bryttian = ____).
brittle; to shatter
_____ deformation is a type of solid state flow that produces a change in the shape of an object without fracturing.
Ductile
Often times when Compressional Stresses and ductile deformation occurs during mountain building, rocks will ___________ much like sheets of paper.
fold or bend
types of folds
anticline, syncline, monocline
When a fold bends upward in an arching shape , an _____ forms.
anticline
When a fold bends downward in the shape of a
trough , a ____ forms.
syncline
When a fold occurs in a step or stair like fashion
a ___ can occur.
monocline
Stresses can also cause a ________ in the earth’s crust to occur due to brittle deformation
fault or fracture
4 main types of faults
normal, reverse, thrust, strike-slip
these are caused by tensional stresses . When this occurs the head (hanging) wall moves down relative to the foot wall
normal fault
When discussing the relative motion of the earth’s crust along faults, the ______ refers to the side of the fault that rests on the foot wall
hanging wall or head wall
The _______ is the side of the fault that appears to
support the head wall or hanging wall.
foot wall
faults that are caused by compressional stress .
reverse faults
In the case of a ____ fault, the hanging wall moves up relative to the footwall.
reverse
these faults are low angle (less than a 45 degree angle) reverse faults.
thrust faults
All faults that move up and down (normal, reverse, and thrust faults) are referred to as _______ faults
dip slip
These faults move side
to side.
strike-slip faults
Where temperatures are high (deep in
Earth’s crust), rocks tend to soften and
become more malleable, so they deform by
folding or flowing (ductile deformation).
Likewise, where temperatures are low (at or
near the surface), rocks tend to behave like
brittle solids and fracture.
the role of temperature
Where temperatures are high (deep in Earth’s crust), rocks tend to ____ and become more malleable, so they deform by folding or flowing (________).
soften; ductile deformation
Likewise, where temperatures are ___ (at or near the surface), rocks tend to behave like ____ solids and fracture.
low; brittle
Confining pressure “_____” the materials in Earth’s crust, which makes it stronger and thus harder to break. Therefore, rocks that
squeezes
thus harder to break. Therefore, rocks that are deeply buried are “______” by the immense pressure and tend to bend rather
than fracture.
held together
For example, igneous and some metamorphic rocks (quartzite, for example) are composed of minerals that have strong internal chemical bonds. These strong, brittle rocks tend fail by fracturing when subjected to stresses that exceed their strength.
the influence of rock type
Sedimentary rocks that are weakly cemented or metamorphic rocks that contain zones of weakness, such as foliation, are more
susceptible to ductile deformation.
the influence of rock type
One key factor that researchers are unable to duplicate in the laboratory is how rocks respond to small stresses applied gradually over long spans of geologic time.
time as a factor
When tectonic forces are applied slowly over long time spans, rocks tend to display _____ behavior and deform by bending or flowing.
ductile
When tectonic forces are applied slowly over long time spans, rocks tend to display ductile behavior and deform by bending or flowing.
time as a factor
For example, marble benches have been known to sag under their own weight over a time span of ___ years or so, while wooden bookshelves may bend within a few months after being loaded with books.
100
For example, marble benches have been known to sag under their own weight over a time span of 100 years or so, while wooden bookshelves may bend within a few months after being loaded with books.
time as a factor
the person that published “ The History of Ocean Basins”
Henry Hammond Hess
The date where “The History of Ocean Basins” was published
1962
The history of ocean basins paved for what?`
seafloor spreading
what did henry hammond hess discover?
He discovered that the oceans were shallower in the middle, and identified the presence of Mid Ocean Ridges.
what does the seafloor spreading theory states?
new ocean crust is being formed at mid-ocean ridges and are being destroyed at deep sea trenches
The crust is subdivided into two types, _____ and
______
oceanic; continental.
______ crust is found under oceans, and it is about four miles thick in most places.
Oceanic
A feature unique to oceanic crust is that there are areas known as ___________ where oceanic crust is still being created.
mid-ocean ridges
Magma shoots up through gaps in the ocean’s floor here. As it cools, it hardens into new rock, which forms brand new segments of oceanic crust.
formation of mid-ocean ridges
Since oceanic crust is _____ than continental crust, it is constantly sinking and moving under continental crust.
heavier
Continental crust varies between ____ and ____ miles in thickness depending on where it is found.
6; 47
_______ crust tends to be much older than the oceanic kind, and rocks found on this kind of crust are often the oldest in the world
Continental
_________ is a geologic process of the movement of two oceanic plates, splitting apart from each other at a divergent plate boundary
Seafloor spreading
It results in the formation of new oceanic crust from magma that comes from within the Earth’s mantle along a mid- ocean ridge.
seafloor spreading
It results in the formation of new _____ from magma that comes from within the Earth’s mantle along a ________.
oceanic crust; mid- ocean ridge
This process is the result of ________. _________ is the slow, swirling motion of Earth’s mantle.
mantle convection
______ carry heat from the lower mantle and core to the lithosphere.
Convection currents
_______ also reutilize lithospheric materials back to the mantle.
Convection currents
Seafloor spreading happens at the ______ plate boundaries.
divergent
As tectonic plates gradually distance from each other, ____ from the mantle’s convection currents makes the crust more __________
heat; plastic and less dense.
The less-dense material ____, often forming a mountain or elevated area of the seafloor.
rises
As a result, the crust cracks. Hot magma powered by ________ bubbles up to fill these fractures and spills onto the crust.
mantle convection
This bubbled-up magma is _____ by frigid seawater to form igneous rock. This rock (______) becomes a new part of Earth’s crust
cooled; basalt
It is the process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle and allows part of the ocean floor to sink back into the mantle.
seafloor spreading subduction
These are large mountain ranges rising from the ocean floor.
mid ocean ridges
Seafloor spreading occurs along ______, though it is not consistent at all _______.
midocean ridges
Seafloor spreading occurs along ______, though it is not consistent at all _______.
midocean ridges
The _______ Ridge separates the North American plate from the Eurasian plate, and the South American plate from the African plate
Mid- Atlantic
Mid-ocean ridge is the ____ of seafloor spreading
actual site
The newest and thinnest crust on Earth is located near the ____ of mid-ocean ridge.
center
The ___, ____, and _______ of oceanic crust increase with distance from the mid-ocean ridge
age, density, thickness
The seafloor has a large mountain range running through it. Deep trenches are found far from the ridges.
evidence for seafloor spreading
The magnetic polarity of the seafloor changes. The center of the ridge is of normal polarity. Stripes of normal and reverse polarity are found symmetrical on both sides of the ridge.
evidence for seafloor spreading
The rocks closest to the ocean ridge were younger than the rocks found further from the ridge. this means that new rocks are formed at the ridges and push the older rocks away from the
ridge based on the core sample collected from 1968, a drilling ship called the Glomar Challenger.
evidence for seafloor spreading
The oldest seafloor is much younger than the oldest continent. The oldest ocean floor rocks ever found are 180 million years old. Remember the Earth is 4.6 billion years old. This proves that ocean floor is being destroyed therefore all ocean floor rocks are young compared to the age of Earth.
evidence for seafloor spreading
Rocks shaped like pillows (rock pillows) show that molten material has erupted again and again from cracks along the mid- ocean ridge and cooled quickly.
evidence for seafloor spreading
Stripes in the seafloor. When magma cools, the iron cools into the mineral magnetite. It lines up parallel to the Earth’s present magnetic field. This iron is like compass needles, pointing north. So, when the rock hardens, a record of the Earth’s magnetic field at that time is locked in stone
evidence for seafloor spreading
Age of rock increases as distance from ridge increases, youngest is at the ridge.
evidence for seafloor spreading
Age of rock increases as distance from ridge increases, _______ is at the ridge.
youngest
The mechanism that operates along the oceanic ridge system to create new seafloor.
seafloor spreading
