Geology Chapter 10

anticlines synclines

2 most common types of folds

compressional stress tensional stress shear stress

3 types of differential stress

strike and dip

Geologists use measurements called ____ and ____ to help determine the orientation of planar rock features, such as sedimentary bedding and fault surfaces

small-scale deformation

_____-____ _______ of rocks by shear stress occur along closely spaced parallel surfaces of weakness, such as foliation surfaces and microscopic fractures where slippage changes the shape of rocks.

strike-slip fault

a fault in which the dominant displacement is horizontal and parallel to the trend (direction) of the fault surface

folds

along convergent plate boundaries, flat-lying sedimentary strata, tabular intrusions, and volcanic rocks are often bent into a series of wavelike undulations called _____

overturned

an asymmetrical fold is said to be _______ if one or both limbs are tilted beyond the vertical.

recumbant folds

an overturned fold that can "lie on its side" so the axial plane is horizontal and are common in highly deformed mountainous regions

deeper crustal

at ____ ______ depths, rocks deform by ductile flow

symmetrical

basic folds described as _____ when the limbs are mirror images of each other

rock structures or geologic structures

basic geologic features that form as a result of the forces generated by the interactions of tectonic plates and include folds, faults, joints, and small scale structures associated with metamorphic rocks such as foliation and rock cleavage

right-lateral strike-slip fault

because movement along the San Andreas Fault causes the crustal block on the opposite side of the fault to move to the right as you face the fault.

tension at shallow depths

cause rocks to fracture and pull apart

shear at shallow depths

causes offsets in crustal blocks along faults

compression

causes shortening

tension

causes stretching

elastic deformation

changes that result from this deformation are recoverable. the rock will snap back to nearly its original size and shape when the stress is removed.

folds

common features of deformed sedimentary rocks that provide evidence that rocks can bend without breaking

strain

differential stress can also change the shape of a rock body, referred to as a _____. Lose their original configuration during deformation

shear stress

differential stress that involves the movement of one part of a rock body past another.

tensional stress

differential stress that pulls apart or elongates rock bodies. Along divergent plate boundaries where plates are moving apart, _____ stresses stretch and lengthen rock bodies

compressional stress

differential stress that squeezes a rock mass as if placed in a vise. Most often associated with convergent plate boundaries. When plates collide, Earth's crust is generally shortened horizontally and thickened vertically.

normal faults

dip-slip faults are classified as ____ ____ when the hanging wall block moves down relative to the footwall block. Tend to be associated with tensional stresses that pull rock units apart, thereby lengthening the crust.

reverse faults

dip-slip faults in which the hanging wall block moves up relative to the footwall block are called ____ _____. result from compressional stresses that produce horizontal shortening of the crust

fault zones

displacements of hundreds of kilometers and consist of many interconnecting fault surfaces and can be several km wide and are often easier to identify from aerial photographs

shear

distorts rock

brittle deformation

dominates in the upper crust, where the temperatures are comparatively cool.

basins

downwarped structures having a similar shape are termed ______. Youngest rocks are found near the center, and the oldest rocks are at the flanks.

hinge line

each layer of a fold is a bent around an imaginary axis called a ____ ____.

dip-slip faults

faults in which movement is primarily parallel to the inclination (also called dip) of the fault surface are called ___ ____ ____.

oblique-slip faults

faults that exhibit both dip-slip and strike-slip movement are caused by a combination of shearing and tensional or compressional stress

detachment fault

faults that represent a major boundary between the rocks below, which exhibit ductile deformation, and the rocks above, which exhibit mainly brittle deformation

axial plane

folds are described by their ___ ____, which is a surface that connects all the hinge lines of the folded strata.

stress

forces that deform rocks. Whenever the ____ acting on a rock body exceed its strength, the rock will deform

faults

fractures in Earth's crust where the rocks on one side of the fault are displaced relative to the rocks on the other side

hanging wall

geologists identify the rock surface immediately above the fault as the _____ _____.

footwall block

geologists identify the rock surface immediately below as the ____ _____

deeply buried rocks

held together by the immense pressure and tend to bend rather than fracture

limbs

in simple folds, the axial plane is vertical and divides the fold into two roughly symmetrical ____.

plunge

in some folds, the hinge lines are included at an angle known as the ____.

fault-block mountains

in the western United States, large normal faults are associated with structures called ____ ____ _____

confining pressure

increases with depth as the thickness of the overlying rock increases. Squeezes the materials in Earth's crust, which makes it stronger and thus harder to break.

klippe

isolated remnant of a thrust sheet that was severed by the erosional forces of glacial ice and running water

monoclines

large, steplike folds in otherwise horizontal sedimentary strata. These folds appear to have resulted from the reactivation of ancient, steep-dipping faults located in basement rocks beneath the plateau.

temperature confining pressure rock type time

major factors that influence the strength of a rock and how it will deform

dip

maximum angle of inclination of the surface of a rock unit or fault, measured from a horizontal plane. Includes both an angle of inclination and a direction toward which the rock is inclined.

grabens

movements along fault-block mountains produced alternating down-dropped fault blocks called ____

horsts

movements along fault-block mountains produced alternating uplifted fault blocks called _____

shearing

often associated with transform plate boundaries, tends to produce fault zones in the upper crust and ductile flow at depth

slickensides

on some fault surfaces, the rocks become highly polished and striated, or grooved, as the crustal blocks slide past one another resulting in these polished and striated surfaces that provide geologists with evidence for the direction of the most recent displacement along the fault

deformation

refers to the changes in the shape or position of a rock body in response to differential stress

Basin and Range Province

region that compasses Nevada and portions of the surround states and the crust has been elongated and broken to create more than 200 relatively small mountain ranges.

depths greater than about 10 km

rocks deform by ductile flow and folding

shallow

rocks exhibit brittle fracture at _____ depths

where temperatures are low

rocks tend to behave like brittle solids and fracture

where temperatures are high

rocks tend to soften and become more malleable, so they deform by folding or flowing

brittle deformation

rocks that break into smaller pieces exhibit this type of deformation. Occurs when stress breaks the chemical bonds that hold a material together

compression at shallow depths

shortening occurs by brittle deformation along faults where one rock mass is thrust over another

transform faults

some strike-slip faults slice through Earth's crust and accommodate motion between two tectonic plates. Numerous transform faults cut the oceanic lithosphere and link spreading oceanic ridges while others accomodate displacement between continental blocks that slip horizontally past each other.

tensional stresses

tend to lengthen rock bodies by displacement along faults in the upper crust and by ductile flow at depth

compressional stresses

tend to shorten and thicken Earth's crust by folding, flowing, and faulting

During elastic deformation

the chemical bonds of the minerals within a rock are stretched but do not break.

strike

the compass bearing (direction) of the line produced by the intersection of an inclined rock layer (or fault) with a horizontal plane. Generally expressed as an angle relative to the north

half-grabens

tilted fault blocks that contribute to the alternating topographic highs and lows in the Basin and Range Province

north-south

topography of the Basin and Range Province evolved in association with a system of normal faults trending roughly ____-____.

thrust faults

type of reverse faults having dips less than 45 degrees, so the overlying block moves nearly horizontally over the underlying block.

ductile deformation

type of solid-state flow that produces a change in the shape of an object without fracturing. May occur by slippage along planes of weakness such as bedding surfaces and foliation in rock bodies

synclines

typically found in association with anticlines are downfolds, or troughs, called _____.

anticlines

usually arise by upfolding, or arching, of sedimentary layers and are sometimes spectacularly displayed along highways that have been cut through deformed strata

fault scarps

vertical displacements along dip-slip faults tend to produce long, low cliffs called ____ _____

gradually

when stress is applied ____, rocks initially respond by deforming elastically

differential stress

when stress is applied unequally in different directions

confining pressure

when stress is applied uniformly in all directions

joints

when tectonic forces cause upwarping of the crust, rocks near the surface are stretched and pulled apart, forming fractures called ___.

dome

when upwarping in basement rock produces a circular or slightly elongates structure, the feature is called a ____. Here, erosion has stripped away the highest portions of the overlying sedimentary beds, exposing older igneous and metamorphic rocks in the center

compression at deeper crustal levels

where temperatures are high, compressional forces squeeze and fold rock masses

shear at deeper crustal levels

where temperatures are high, shear stress distorts rock masses by ductile flow, usually along shear zones

tension at deeper crustal levels

where temperatures are high, tensional forces stretch and elongate crustal materials by ductile flow