Test 2 (Lectures 4-8) Pt. 3 Flashcards
What are metamorphic rocks?
Pre-existing rocks that have undergone solid-state changes
What does the word “meta” stand for?
Change
What does the word “morphe” stand for?
Form
The preexisting rocks that are altered during metamorphism are called
Protoliths
Metamorphism can alter to what type of protoliths?
- Igneous
- Sedimentary
- Metamorphic
Protoliths undergo changes in what?
- Texture
- Mineralogy
Why do protoliths undergo these changes?
They can happen due to:
- temperature
- pressure
- tectonic stress
- the amount of reactive water
What are some metamorphic processes?
- Recrystallization
- Neocrystallization
- Pressure solution
- Plastic Deformation
What is recrystallization?
When minerals change shape and size through dissolution and growth of crystals. Ex - limestone to marble
What is neocrystallization?
Formation of new metamorphic minerals from old (those from protoliths)
What is pressure solution?
When mineral grains partially dissolve where their surfaces press together
What is plastic deformation?
When mineral grains soften and deform when rock is squeezed or sheared at elevated temperature and pressure
What are the two different kinds of differential stress?
- Normal
- Shear
Why does differential stress occur?
It’s a result of tectonic forces
Mountain building creates a horizontal compression ___; rifting creates a horizontal extension _____
Push; pull
How does normal stress work?
Operates perpendicular to a surface
What is compression?
Push-together normal stress
What is tension?
Pull-apart normal stress
How does shear stress work?
It acts as a parallel to the surface
How does differential stress occur?
It causes inadequate mineral shapes to align in preferred orientations
Why does foliation develop?
The rocks have been subjected to differential stress
What is foliation?
A planar fabric that cuts through the rock
What are some foliated metamorphic rocks?
- Phyllite
- Schist
- Metaconglomerate
- Gneiss
What are some non-foliated metamorphic rocks?
- Quartzite
- Marble
What are the different types of metamorphism?
- Thermal
- Burial
- Dynamic
- Regional
- Hydrothermal
- Subduction
- Shock
What is contact (or thermal) metamorphism?
Metamorphism that is due to heat from a body of magma invading host rock
Dynamic metamorphism involves
A breakage of rock by shearing within a fault zone
When does dynamothermal tend to occur?
It occurs during the development of mountain belts. This process is also called regional metamorphism.
What does directed compression do?
Smashes pre-existing rocks and buries them deeply where they get heated by geothermal gradient and plutonic intrusions
What is hydrothermal metamorphism?
When hot, chemically, aggressive water chemically alters basalt
What is subduction metamorphism?
When trenches and accretionary prisms have a low geothermal gradient
What are shields?
Large regions of ancient high-grade metamorphic rocks are exposed in continental interiors
Mountains occur in elongate curvilinear ____ or ____
Belts; orogens
Mountain building is a process called
Orogenesis
Mountains reflect the geologic processes of
- Uplift
- Deformation
- Metamorphism
Mountain building involves many geological processes such as
- Deformation
- Jointing
- Faulting
- Forming
What does deformation do?
It changes the character of rocks
Where does brittle deformation mainly occur?
It occurs in the shallower crust
What are the two major deformation styles?
Brittle and ductile
What is strain?
The change in shape caused by deformation or by a leading force (stress)
Stress
Force applied across a unit area
What are the different types of stress?
- Compression
- Tension
- Shear
- Pressure
What is compression?
When an object is squeezed
What is tension?
When the ends of an object are pulled apart
What is shear?
When surface slide past each other
What is pressure?
When an object feels the same pressure from all sides
The geometry of planar surfaces during rock formation is described using
Strike and slip
Dip is always ___ to strike
perpendicular
What are joints?
Planar rock features without any offset to develop from tensile stress in brittle rock
Fractures filled with minerals are called
Veins
What are faults?
Planar fractures that show offset
The amount of offset is called?
Displacement
What are some fault motions?
- Dip-slip faults
- Strike-slip faults
- Oblique slip faults
In a normal fault, the hanging wall moves..
Down
In a reverse fault, the hanging wall moves…
Up
In a thrust fault the hanging wall is..
A reverse fault with a 30-degree dip
Strike-slip faults have fault motion ____ to the strike of the fault
Parallel
Slickensides and linear grooves are
Slip lineations
Fault scarps are visible when
Faults intersect the surface
What is a hinge?
A line along which curvature is greatest
What are limbs?
Less curved “sides” of a fold
What does the axial plane do?
Connect hinges of successive layers
What is an anticline?
A fold that looks like an arch
What is a syncline?
A fold that opens outward like a through
What is a dome?
A fold with the appearance of an overturned bowl
What is a basin?
A fold shaped like an upright bowl
Where are the youngest rocks found in a basin?
They’re found in the basin
Where are the youngest rocks found in a dome?
They’re found in the sides or the corners
