Chapter 8
Horst
A raised fault block surrounded by paralledl (graben) faults
Deformation of grains and clasts
Clasts that were initially spherical are flattened like pancakes
_____per unit is_____
Force, stress
Marble probable rock origin
Limestone
Fold in which rocks fold down in the shape of a U is a
syncline
Vertical joints
tectonic stresses
Deep Depth Rock Effects
-Ductile behavior occurs, flowing of the rock -Minerals recrystallize into larger or smaller crystals -High-temperature veins form; mobilization of chemical constituents
Stress Field Different Arrows
-Force greater in some directions than in some others -Differential stress -Occurs when tectonic forces affect the rock
Stress Field Equal Arrows
-Force same from all directions -Confining pressure
Dip-Slip Fault
-Hanging wall falls down relative to footwall -Created through tension
What happens to a sedimentary rock as it metamorphoses to become metamorphic rock
-Minerals present may change -Crystals of minerals may become larger with higher grade metamorphism -Rock texture may change
Which of the following may be the truth of metamorphic rocks
-Most metamorphic rocks have folds. -They have preserved structures from before the rock was metamorphosed. -They contain flattened or folded pebbles. -They display shear zones.
How do geologists determine the stability conditions of minerals buried at great depths?
-Observing deep rocks that were uplifted due to tectonics and exposed -Conducting laboratory experiments with high-temperature and high-pressure conditions
Causes of metamorphism
-Pressure and temperature increases associated with increasing depth -Temperature increases from nearby magma bodies -Temperature increases due to hot fluids carrying material into, through, and out rocks -Pressure increases associated with tectonic stresses
Shallow Depth Rock Effects
-Rock shows brittle behavior, fracture in the rock -Minerals are stable and barely respond to conditions -There is little effect, may form low-temperature mineral veins
Strike Slip Fault
-Rocks slide lateral to each other -Created with side-to-side motion parallel to strike
Reverse Dip Slip fault
-hanging wall goes above footwall -Created through horizontal compression
Rank the following in order for the formation of a fault from a cylinder of rock in a lab. Place the first step on the top and the last step on the bottom
1.Compressive stress is applied parallel to the axis of the cylinder. 2. Rock experiences internal strain and is shortened slightly. 3. Stress exceeds strength of the rock and a fracture forms. 4. Slip occurs along the fracture.
Order of how a rock responds to progressively increasing stress, starting with little stress
1.Rock does not change at all 2. Rock behaves elastically but remains undeformed 3. As stress becomes larger than strength of rock, rock begins true deformation 4. Rock fails structurally, either by folding, fracturing, or flowing as a ductile solid
Graben
A depressed block of land bordered by parallel (horst) faults
Gneiss
Alternating dark and light bands, banded, compositional foliation
Overturned fold geometry
Axial surface is inclined such that a limb has been rotated more than 90 degress
Asymmetric fold geometry
Axial surface is inclined to Earth's surface
Upright fold geometry
Axial surface is vertical
Hanging Wall
Block of rock above an inclined fault
Footwall
Block of rock below the fault
Differential Stress Types
Compression(towards the objects), shear(parallel towards the object), tension(Away from the object)
Columnar joints
Cooling, contracting stresses
Rotation
Elongated and platy minerals become nearly parallel to one another during compression
Normal Fault
Fault lines that cause grabens and horsts
Marble
Fine- to coarse- grained calcite; metamorphosed limestone
Greenstone
Fine-grained greenish rock; may be metamorphosed mafic volcanic rock
Non-plunging fold geometry
Fold hinge is horizontal
Plunging fold geometry
Fold hinge is inclined from the horizontal; may be gentle, moderate, or steep
Amount of acceleration experienced by a mass
Force
Faults
Fractures along which rock has slipped relative to the other side
Joints
Fractures that are simple cracks where the rock has pulled apart by a small amount
Regional metamorphism
Heating and deformation over large areas
Greenschist probable rock origin
Mafic volcanic rock
Force divided by the area on which it is applied
Mass
Schist
Mica crystals that are large enough to see with the naked eye
Metamorphism
Mineralogical or rock texture changes take place
Deformed granite probable rock origin
Plutonic rock
Metarhyolite probable rock origin
Rhyolite
Deformation
Rock subjected to heat and pressure, folding, faulting, shearing
Contact metamorphism
Rocks are heated locally and have little associated deformation
Oblique Slip Fault
Rocks slip both vertically and laterally
Slate probable rock origin
Shale
Phylitte
Sheen present due to microscopic minerals
Special geologic term used to represent the direction of a horizontal line on an inclined surface(like in a fault) and the angle of that surface to the horizontal are
Strike and dip
Horizontal joints
Tensional stresses in a horizontal direction
Quartzite
Tightly merged quartz crystals; metamorphosed sandstone
Shearing
Unorientated crystals are stretched or aligned, smeared out, broken or recrystallized zones may form
Unloading joints
Uplift and reduced pressure
Cleavage
When rocks are under low to moderate temperatures (>300 degrees celsius), they may develop a planar fabric along which they break called cleavage
Fold in which rock layers warp up in the shape of an A is a
anticline
The center of a _____ has rocks that are younger than those in the surrounding areas
basin
The______ dip of a rock structure, like a fault, is the angle the surface makes with the horizontal. The direction of a horizontal line on an inclined surface is the_______
dip, strike
The center of a_____has rocks that are older than those in the surrounding area
dome
A fold that has layers dipping in only one direction is called a
monocline
