Chapter 4 Flashcards
study of rock units’ three-dimensional distribution and deformation history.
structural geology
It specializes with understanding how rocks respond to tectonic forces, as well as the processes that cause formation to geologic structures like folds, faults, and joints.
structural geology
its objective is to understand the history of deformation in the Earth’s crust and predict the mechanical behavior of rocks under various stress conditions. Intense geologic activities occur at plate boundaries where plates move away from one another, past one another, or toward one another.
structural geology
is the idea that continents move freely over the earth’s surface, changing their positions relative to one another.
continental drift
he noted that geographic fit of continents e.g. Africa and South America, Atlantic formed by separation of Africa from South America, and speculates that earthquakes and flooding may have the separation possible.
Abraham Ortelius
he proposed supercontinent by studying fossils, rocks, mountains.
Seuss
proposed continental drift and Pangaea, and claimed that there used to be only one supergiant landmass where all continents came from.
Wegener and Taylor
suggested the idea of thermal convection as the driving force for the movement of continents.
Arthurs Holmes
- Continents seem to fit together like pieces of a puzzle
Geographic Fit
Supporting Evidences of Continental Drift:
Fossils
Coal Seams
Mountains
Glacial Deposits
Similar distribution of ___________ such as Mesosaurus have been found in different regions and continents.
Fossils
Usually, coal is found in tropical areas because the climate is warm and ideal for the propagation of organisms. Coal would be found in polar regions such as North Pole and Antarctica.
coal seams
Usually, _____________is found in tropical areas because the climate is warm and ideal for the propagation of organisms. ___________would be found in polar regions such as North Pole and Antarctica.
coal
coal
Mountain ranges match across oceans (similar rock layers & rock types).
mountains
Places that are presently known to tropical and desert like such as Africa, Madagascar and India finding ice deposits would seem unreasonable if not for the concepts of drifting continents.
glacial deposits
is a hypothesis that the sea floors form at the crest of the mid-oceanic ridge, then move horizontally away from the ridge crest toward an oceanic trench.
Sea-floor Spreading
is a continuous process where tensional forces on both sides of plate cause them to constantly move apart.
Sea-floor Spreading
Sea-floor spreading suggests that the seafloor moves away from the mid-oceanic ridge as a result of _____________.
mantle convection
who developed sea-floor spreading
Harold Hess and Robert Dietz
is the sliding of the seafloor beneath a continent or island arc.
Subduction
Hess hypothesis was that seafloor spreading is driven by ___________________.
deep mantle convection.
is a circulation pattern driven by the rising of hot material and/or sinking of cold material.
Convection
In seafloor spreading, ____________ rises to the surface from the mantle. In time magma is cooled by seawater and forms the ____________ crust. New________________ created at the mid-ocean ridge and destroyed in deep ocean trenches.
magma
oceanic
sea floor
Supporting Evidence for Seafloor Spreading
World Seismicity
Volcanism
Age of Sea floor
Paleomagnetism
Heat flow
Earthquake distribution matches plate boundaries.
World Seismicity
Volcanoes match some plate boundaries; some are hot spots.
Volcanism
___________ Seafloor is at mid-ocean ridge; ________ sea floor away from mid-ocean ridge.
Youngest
oldest
___________ sea floor is continually being formed by basalt eruptions at the ridge crest. This basalt is then carried sideways by convection and is subducted in to the mantle at an oceanic trench.
New, young sea floor is continually being formed by basalt eruptions at the ridge crest. This basalt is then carried sideways by convection and is subducted in to the mantle at an oceanic trench.
___________ seafloor is continually being destroyed at trenches, while ________ sea floor is being formed at the ridge crest.
old new
old seafloor is continually being destroyed at _________ , while new sea floor is being formed at the ____________.
trenches
ridge crest
Because the ocean floor is mostly composed of basalt, an iron-rich substance containing minerals that align with the magnetic field, they record the alignment of the magnetic fields surrounding oceanic ridges.
paleomagnetism
Studies conducted with thermal probes, for example, indicate that the heat flow through bottom sediments is generally comparable to that through the continents except over the mid-ocean ridges, where at some sites the heat flow measures three to four times the normal value. The anomalously high values are considered to reflect the intrusion of molten material near the crests of the ridges.
Heat Flow
________________ combined ideas of continental drift and seafloor spreading into “Plate Tectonics”.
John Tuzo Wilson
It is the combined ideas of continental drift and seafloor spreading into
Plate Tectonics
is a large mobile slab of rock that is part of the Earth’s surface.
Plate
Its interior is inactive tectonically.
Plate
Plates interact with each other along their edges (_____________________) that has a high degree of tectonic activities which causes the geologic processes such as earthquakes, etc. Earth’s outermost layer composed of thin rigid plates moving horizontally.
(plate boundaries
is the rising of Earth’s crust to higher elevations.
Uplift
is the sinking of regions of Earth’s crust to lower elevations.
subsidence
Rocks that are uplifted _____ or ___________ be highly deformed.
may or may not
Rocks that subside ________ undergo deformation.
do not
There are three types of plate boundaries based on the movement.
Divergent Plate Boundary
Convergent Plate Boundary
Transform Plate Boundary
is boundary between plates that are moving apart, creating new crust.
Divergent Plate Boundary
These boundaries are typically found along mid-ocean ridges, where seafloor spreading occurs. As the plates separate, magma rises from below to fill the gap, creating new oceanic crust.
Divergent Plate Boundary
lies between plates that are moving toward each other.
Convergent Plate Boundary
At these boundaries, plates collide.
Convergent Plate Boundary
When two plates of different densities meet (for example, an oceanic and a continental plate), the denser plate is forced beneath the lighter one in a process called ______________.
subduction
This leads to the formation of deep ocean trenches and volcanic mountain chains.
Convergent Plate Boundary
In the case of two continental plates colliding, ________________s like the Himalayas are formed.
massive mountain range
is where one plate dives or subducts under the other.
ocean to ocean convergence
is where the dense oceanic plates under the continental plate. Forms an active continental margin between the trench and the continent.
ocean to continent convergence
is where the plates collide and crumble but neither is subducted.
continent to continent convergence
is at which two plates move horizontally or laterally past each other.
transform plate boundary
In transform plate boundary, __________ is neither created nor destroyed.
Crust
Most common type of transform fault occurs on fracture zones and connects two divergent plate boundaries. These boundaries are characterized by ___________ faults and can generate significant earthquakes, as seen along the San Andreas Fault in California.
strike-slip
These are forces that tends to move or change the orientation of the plate (along earth’s crust)
tectonic forces
Deep within the Earth’s crust, rocks are constantly being squeezed, stretched, and sheared. This process is known as ______________, and it is driven by forces that cause rocks to bend, break, or flow.
rock deformation
When studying rock deformation, geologist typically refer to ___________ , a force per unit area or the force applied to a material, divided by the area over which it is applied.
stress
stress produces ___________ which is when there’s a change in size (volume), shape, or both while an object is undergoing stress.
strain
3 kinds of stress
tensional stress
compressive stress
shear stress
caused by forces pulling away from one another from opposite directions. It causes stretching or extensional strain.
tensional stress
It is common at divergent boundaries, where tectonic plates are moving away from each other.
tensional stress
causes rocks to become thinner and can lead to the formation of normal faults.
tensional stress
caused by forces pushing or squeezing towards one another in an opposite direction.
compressive stress
It causes shortening strain.
compressive stress
It occurs at convergent boundaries, where plates collide
compressive
results in the thickening of the crust and the formation of mountains, as well as the development of reverse faults.
compressive
due to movement parallel to but in opposite directions along a fault or other boundary.
shear stress
It causes shear strain. It is most commonly found at transform boundaries, where plates move laterally.
shear stress
This type of stress can result in strike-slip faults.
shear stress
Behaviors of Rocks to Stress and Strain
elastic
ductile
brittle
is if the deformed body recovers its original shape after the stress is reduced or removed.
elastic
is the maximum stress or force per unit area within a solid material that can arise before the onset of permanent deformation.
elastic limit
is if it bends while under stress and does not return to its original shape after relaxation of the stress
ductile
Are folds elastic, ductile, or brittle?
ductile
This type of deformation occurs at higher temperatures and pressures, deep within the Earth.
ductile
is if it breaks or creates a fracture at stresses higher than its elastic limit
brittle
Are faults elastic, ductile, or brittle?
brittle
Are joints elastic, ductile, or brittle?
brittle
This type of deformation is typical of rocks in the upper crust, where temperatures are lower and rocks are more rigid.
brittle
are natural breaks or cracks in rocks, often occurring due to tectonic stresses or rock deformation
fractures
are fractures without significant displacement.
joints
formed when tension and compression associated with plate movement is so great that blocks of rock fracture or break apart
faults
______________ of a non-horizontal bed, is the compass orientation of a line formed by the intersection of an imaginary horizontal plane with the inclined bedding plane.
strike
___________________of the inclined rock layer is the angle between the imaginary horizontal plane and the inclined rock layer.
Dip
It is formed from movement of rock along the dip of the fault plane.
Dip-slip Faults:
3 types of dip=slip faults
normal fault
reverse fault
thrust fault
forms when the hanging-wall rock moves downward compared to the footwall. This occurs when rocks move away from each other due to the land moving apart.
normal fault
is formed if the hanging wall moves up along a dip-slip fault compared to the footwall and if the fault dips at an angle steeper than 45 degrees.
reverse fault
is formed if the fault dips at an angle less than 45 degrees.
thrust fault
It is formed by horizontal movement along the strike direction of the fault plane.
strike-slip fault
forms if features appear shifted to the left from one side of the fault to the other.
Left-lateral Strike-slip Fault
forms if features shift to the right across the fault.
Right-lateral Strike-slip Fault
It is a combination of dip-slip and strike-slip movements in which diagonal motion occurs along the fault plane, both along the strike and dip.
Oblique-slip Faults:
is formed when two normal faults occur parallel to each other and the land sinks between the faults.
Rift Valley or Graben
is the opposite of a rift valley where the land between the parallel faults is forced upward because the two faults are being pushed together.
Horst
Graben or Horst?
Compressive and forced upward
Horst
Graben or Horst?
Tensional and sinks in
Graben
are bends or wave like features in layered rock. It occurs with convergent or compression motion.
folds
. It is usually strained in a ductile way than elastic or brittle strain.
folds
are arched folds where limbs dip away from the hinge line.
ANTICLINES
Oldest rocks are exposed along the hinge line.
anticlines
are trough-shaped folds where limbs dip toward the hinge line.
syncline
Younger rocks are exposed along the hinge line.
syncline
is a type of fold in which limbs are parallel to each other, implies intense compressive stress.
isoclinal folds
is a type of fold in which upper limb of the fold override the lower limb that implies unequal compressive and/or shear stress.
overturned fold
is a type of fold that are overturned to such an extent that the limbs are essentially horizontal and indicates compressive and/or shearing stress is more intense in one direction.
recumbent folds
