geology test 3

If strike and dips symbols were placed on a map of a basin, which way would the dips point?

Dips point down toward the center.

-What are the differences between burial and regional metamorphism? - Which is more extensive? -Where does each type occur? -Describe the stresses associated with burial versus regional metamorphism.

burial - sedimentary rocks are buried even deeper regional - when temp. and pressures increase beyond range of burial metamorphism; occurs under places with high temp and ressure over large areas regional is more extensive

Which type of force is responsible for reverse fault formation?

compressional force

What is the hinge line of a fold?

line of maximum inflection that layers wrap around

Which of the following examples best illustrates the effects of ductile deformation?

Rocks along a convergent plate boundary are subjected to compressive force for millions of years and are permanently folded.

What are rocks below and above a fault called?

the footwall below and the hanging wall above

Which of the following images best describes how a rock in the deep crust would be deformed as a result of shear stress?

Because the rocks are at depth, the rocks will distort, but not fracture.

How will the orientation of a plunging anticline's limbs change in the direction the fold is plunging?

They will close to a point.

-Describe how foliation is produced in a metamorphic rock (3 mechanisms). -Name two common platy minerals that produce foliation in metamorphic rocks. -Can non-platy minerals exhibit foliation (think metaconglomerate)?

1. preferred mineral orientation - perpendicular to stress 2. alternating mineral bands - compositional layers (light and dark) 3. mineral flattening - grains elongate and flatten

Which of the following scenarios best describes the deformation that will occur in different parts of the crust?

Brittle deformation is dominant in the shallow crust; ductile deformation is dominant in the deep crust.

What is the orientation of a fold's hinge line with respect to the orientation of plunge?

Hinge line is in the direction of plunge.

Imagine a fold has been eroded to a flat surface. In general, how would you know whether this fold is plunging?

Nonplunging folds look like straight lines at the surface, and plunging folds look like wavy lines.

Which of the following statements best describes the orientation of rock layers for a structural dome or structural basin?

Rock layers wrap around a single point.

Imagine a syncline has been eroded to a flat surface. How would the rock age change as you walked across that flat surface?

Rocks would be oldest on the edges and youngest in the middle.

Imagine an anticline has been eroded to a flat surface. How would the rock age change as you walked across that flat surface?

Rocks would be youngest on the edges and oldest in the middle.

When viewed from the air, the Bighorn River cuts across the Sheep Mountain anticline. As Sheep Mountain is a topographic high and barrier to streamflow, how was the river able to establish itself and eventually erode through the anticline?

The Ancestral Bighorn River established a course over the landscape while the anticline was still buried at depth.

What produces plunging folds?

a combination of folding and tilting

What is a syncline?

a fold shaped like a right-side-up U

What is an anticline?

a fold shaped like an upside-down U

Which type of force causes folding?

compressional force

What is the difference between differential stress and confining pressure? Which of these two stresses is most likely to produce foliation in a metamorphic rock?

differential stress - forces are unequal in different directions confining pressure - squeezes rock equally in all directions differential stress is most likely to produce foliation in a metamorphic rock

The anticline that makes up Sheep Mountain is rather small and restricted in extent. What other local feature might be present that would constrain this fold to a small geographic area?

faults in the basement rock beneath the anticline.

-What are migmatites? -How do migmatites form? -Do they represent low or high temperatures?

forms at temperatures exceeding 700 degrees C where gneiss partially melts felsic minerals melt, mafic minerals remain solid silica-rich liquid invades partially melted rock softened rock contorts and deforms

What is a fault?

fractures along which rocks move

-What are index minerals? -How are index minerals used in mapping metamorphic terrain?

good indicators of the metamorphic conditions under which they were formed (only present for short amount of time)

What are the agents of metamorphism?

heat, pressure, chemically active fluids

-Know how the different types of metamorphism are related to plate tectonics. -In terms of tectonic environments, where would you find each of the following metamorphic conditions: high-temperature/low-pressure, high-temperature/high-pressure, low-temperature/high-pressure, and hydrothermal metamorphism.

high-temp/low-pressure ---> high-temp/high-pressure ---> low-temp/high-pressure ---> hydrothermal metamorphism --->

A series of synclines and anticlines is oriented with the hinge lines of the folds trending east-west. From which directions did the force come to create these folds?

north-south

Describe hydrothermal metamorphism. What types of reactions occur? Where does hydrothermal metamorphism occur?

occurs along mid-ocean ridges where heated seawater percolates through hot, fractured basalt crustal rocks on continents can react with invading, hot fluids associated with igneous intrusions

Describe contact metamorphism. Where does it occur? What type of geothermal gradient is associated with contact metamorphism? What is a contact metamorphic aureole?

occurs at high temperatures, adjacent to magma chambers; restricted to a small area round the margins of a magmatic intrusion

In what tectonic environment do blueschists and eclogites form?

progressive metamorphism of basalt blueschist - very high pressures, relatively low temperatures eclogites - extremely high pressures, moderate-high temperatures

-What is cataclastic metamorphism? -Where does it occur? -What is the difference between a fault breccia and mylonite?

results form the crushing and shearing of rock during tectonic movement occurs along fault planes

Brittle deformation is dominant in the shallow crust; ductile deformation is dominant in the deep crust.

reverse faulting folding

Which type of force is responsible for normal strike-slip formation?

shear force

Rank the following metamorphic rocks in order of increasing grade of metamorphism: schist, granulite, phyllite, slate, gneiss.

slate phyllite schist gneiss granulite

Identify the parent rock for each of the following metamorphic rocks: slate, quartzite, marble, greenstone, and anthracite.

slate ---> shale quartzite ---> sandstone marble ---> limestone greenstone ---> basalt anthracite ---> bituminous coal

Which type of fault has NO vertical motion of rocks associated with it?

strike-slip fault

Which of the following processes resulted in the deformation of sedimentary units in the American West during the Jurassic Period?

subduction of the Farallon plate beneath the North American plate

Which tectonic stress will result in a lengthening of the crust?

tension

Which type of force is responsible for normal fault formation?

tensional force