Summa 2 Flashcards by mork .

Changes rock via temperatures and/or pressures unlike those in which it initially formed

metamorphism

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All metamorphic rocks have a _______ (the rock from which it formed)

parent rock

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the rock from which it formed

parent rock

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______________ can be igneous, sedimentary, or other metamorphic rocks.

Parent rocks

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Change occurring during metamorphism

metamorphic grade

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Progresses from low grade (low temperatures and pressures) to high grade (high temperatures and pressures)

metamorphic grade

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low temperatures and pressures

low grade

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high temperatures and pressures

high grade

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During metamorphism, the rock must remain essentially _____

solid

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the different drivers of metamorphism

heat, confining pressure, differential and compressional stress, chemically-active fluids

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Most important agent

heat

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two sources of heat

geothermal heat and contact metamorphism

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an increase in temperature with depth (about 25o C per kilometer)

geothermal gradient

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rising mantle plumes

contact metamorphism

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Forces are unequal in different directions

differential stress

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Causes the spaces between mineral grains to close

confining pressure

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Forces are applied equally in all directions

confining pressure

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Rocks are squeezed as if in a vice
Shortened in one direction and elongated in the other direction

compressional stress

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Enhances migration of ions

chemically-active fluids

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Aids in recrystallization of existing minerals`

chemically-active fluids

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metamorphic textures

foliated, non-foliated, porphyroblastic

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Rock or slaty cleavage

foliated

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Split into thin slabs

foliated

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Low-grade metamorphism

foliated

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Platy minerals (mica) are visible

Schistosity

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Exhibit a planar or layered structure

schistosity

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Rocks having this texture are referred to as schist

schistosity

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some textures of foliated

schistosity, gneissic,

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High-grade metamorphism, segregation of minerals into light and dark bands

gneissic texture

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Metamorphic rocks with this texture are called gneiss

gneissic texture

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Gneiss does not ____ as easily as slates and schists

split

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______ composed of minerals that lack layering/foliation

Nonfoliated

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Large grains (porphyroblasts) surrounded by a fine-grained matrix of other minerals

porphyroblastic

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examples of foliated rocks

slate, phyllite, schist, gneiss

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example of non-foliated rocks

marble, quartzrite

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-Very fine-grained
-Excellent rock cleavage
-Most often generated from low-grade metamorphism of shale, mudstone, or siltstone

slate

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-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

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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

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-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

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-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

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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

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quart sandstone will undergo metamorphism under increase in temperature and pressure to form?

quartzite

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shale

very fine-grained

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slate

fine-grade

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schist

medium to coarsed-grained

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gneiss

coarse-grained

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parent rock of slate

shale, mudstone, or siltstone

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parent rock of phylllite

shale, mudstone, or siltstone

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parent rock of schist

shale, mudstone, or siltstone

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parent rock of gneiss

shale, granite, or volcanic rocks

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parent rock of marble

limestone, dolostone

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parent rock of quartzite

quartz sandstone

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parent rock of hornfels

often shale, but can have many composition

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If the sedimentary rock limestone or dolomite is metamorphosed it can become the metamorphic rock ____.

marble

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If the sedimentary rock sandstone is metamorphosed it can become the metamorphic rock ____.

quartzite

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If the sedimentary rock shale is metamorphosed it can become the
metamorphic rock ___.

slate

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If the metamorphic rock slate is metamorphosed it can become the metamorphic rock ____

phyllite

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If the metamorphic rock phyllite is metamorphosed it can become the metamorphic rock ____.

schist

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If the metamorphic rock schist is metamorphosed it can become the metamorphic rock ___.

gneiss

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metamorphic environments

-contact or thermal metamorphism
-burial metamorphism
-subduction zone metamorphism
-regional metamorphism
-impact metamorphism

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Results from a rise in temperature when magma invades a host rock

contact or thermal metamorphism

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Occurs in the upper crust (low pressure, high temperature)

contact or thermal metamorphism

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The zone of alteration (aureole) forms in the rock surrounding the magma

contact or thermal metamorphism

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The zone of alteration (______) forms in the rock surrounding the magma

aureole

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Associated with very thick sedimentary strata in a subsiding basin
Gulf of Mexico is an example

burial metamorphism

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Sediments and oceanic crust are subducted fast enough that pressure increases before temperature

subduction zone metamorphism

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Creates the most metamorphic rock

regional metamorphism

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Associated with mountain building and the collision of continental blocks

regional metamorphism

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Occurs when meteorites strike Earth’s surface

impact metamorphism

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Product of these impacts are fused fragmented rock plus glass-rich ejecta that resemble volcanic bombs

impact metamorphism

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Product of these impacts are fused fragmented rock plus glass-rich ejecta that resemble volcanic bombs that are called

impactiles

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______ (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

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.