Earth Science, Tarbuck Chap 7 Flashcards
force applied equally in
all directions is called
Confining Pressure
What does Confining pressure do to rocks
compacts mineral grains to reduce the volume of rock bodies. Note that Confining Pressure does not cause Deformation
Deformation is caused by
Differential Stress
3 types of differential Stress
Compressional, Tensional, Shear
What is compressional Stress
squeezes a rock mass. Associated with convergent boundaries
What is Tensional Stress
pulls apart rock bodies. Associated with Divergent boundaries
What is Shear Stress
movement of one part of a
rock body past another. Associated with transform boundaries
What is Strain?
When differential stress changes a rock’s shape, the resulting deformation is called strain.
What is another way other than strain Mineral Grains change responding to Differential Stress
Recrystallization of the Crystals caused by movement of atoms from high to low stress
What are the types of deformation that lead to strain
elastic, brittle, and ductile
What is elastic deformation
A temporary shape change that is self-reversing after the force is removed, so that the object returns to its original shape
What is Brittle Deformation
When a rock is deformed beyond its ability to respond elastically, rocks that break into smaller pieces undergo Brittle deformation
What is Ductile Deformation
slippage along surfaces of weakness within the rock and the gradual reshaping of mineral
grains. This can cause some rocks to flow very slowly
What happens to rocks when temperature is higher
Rocks can undergo Ductile deformation more easily
Order from smallest to largest temperature gradients and why: Mid-ocean Ridge, Hot spots, Subduction zones
Subduction zones(Cool oceanic crust goes deeper into the mantle, leading to small temperature gradients), Hot Spots(Both Mid-ocean ridges and Hot spots have large temperature gradients but mid-ocean ridges typically have the most elevated geotherms because their unusually thin crust allows hot mantle to push up near the surface), Mid-ocean Ridges
When temperatures are lower, what commonly occurs to a rock
Brittle Deformation is common
As confining pressure increases, what happens to rocks
Rocks are harder to break
What are Folds
Along convergent plate boundaries, rock strata are often
bent into a series of wavelike undulations
What is an anticline fold
arching of sedimentary layers
What is a Syncline Fold
Downfolds or troughs
Basic Folds are described as _______ or _________ folds
Symmetrical or Asymmetrical
A fold is said to be Overturned when
both limbs dip in the same direction
What is a recumbent fold
axial plane is horizontal
What is a plunging fold
when hinge lines penetrate Earth’s surface
What is a dome
broad, upward bulge in rock layers, forming a roughly circular or oval shape
What is a Basin
inverse of a dome, a downwarped structure
What are Monocline Folds
large, steplike folds
What is a fault
fracture along which motion has occurred, so that the rocks on either side are offset from each other. Caused by Brittle Deformation
What are dip-slip faults
movement is primarily parallel to the slope of the fault surface
What is Dip?
angle at which the fault surface is inclined relative to the horizontal.
What is Hanging wall block in a fault
Hanging wall block is the wall block that is “hanging” on the footwall
What are fault scarps
long, low cliffs due to vertical displacement along dip-slip faults
What is a normal fault
hanging wall block moves
down relative to the footwall block. Caused by Tensional Stresses
What are fault-block mountains
large normal faults that can form to create mountains
What are horsts and grabens
Horsts are uplifted fault blocks, while Grabens are down-dropped block
What are Reverse and Thrust Faults
hanging wall block moves up relative to the footwall
What causes reverse and thrust faults to from
Compressional Stresses
Difference between reverse and thrust faults
Thrust faults are reverse fault in which the fault’s angle is less than 45 degrees.
What are Strike-Slip Faults
Fault’s dominant displacement is horizontal. Caused by Shear stress
What are Joints
brittle-fracture surface in rocks along which little or no displacement has occurred.
Most joints are formed from ______ stresses
tensional
Processes that produce a mountain belt are collectively termed
Orogenesis
What is an orogeny
episode of mountain building
What is an accretionary wedge
accumulation of deformed and thrust faulted sediments and scraps of ocean crust scraped onto the edge of the overriding plate in subduction zones
What is a forearc basin
region between Accretionary wedge and volcanic arc formed when the accretionary wedge builds up enough sediment to protrude through the ocean and form a basin.
What is a terrane
crustal fragment that consists of a distinct and recognizable series of rock formations and has been transported and accreted by plate tectonic processes.
What is a suture
zone where two continents collide and are “welded” together
What is Isostatic Adjustment
process of establishing a new
gravitational balance in response to loading or unloading in the crust
What is Isostasy concept
crust floats in gravitational balance in the mantle
What is Gravitational Collapse in a mountain
rocks deep within the developing mountain, which are relatively warm and weak, begin to flow laterally as gravity pulls the mountain downwards
