Petro Lecture Final Flashcards
Define Metamorphism
a subsolidus process leading to changes in mineralogy and/or texture
What are the effects of increasing temperature in metamorphic reactions
Promotes recrystalization, drives reactions, and overcome kinetic barriers
How are upper and lower limits of metamorphism defined
Upper limits begins when the rock begins to melt. Lower limit begins when the tem or pressure is too low for crystals to form.
Are the upper and lower limits the same for different protoliths
No, the crystal formation varies on composition
Explain how and why the lithostatic and hydrostatic pressure gradients are different
Lithostatic: vertical gradient of pressure caused by a column of ROCK
Hydrostatic: vertical gradient of pressure caused by a column of WATER
Describe the three types of deviatoric stress
Compression
Tension
Shear
Order of Stress for Lineation
Max= intermediate >min
Sausage
Order of stress of Foliation
Max>intermediate=min
cookie
order of Stress of Lineation-foliation
Max>intermediate>min
soap
How are fluids involved in metamorphism
In fluid inclusions, and for hydrous and carbonate phases
How are fluids involved in metamorphism
Fluid inclusions
Fluids required for hydrous and carbonous phases
What are the sources of fluid in metamorphism
Meteoric, juvenile magmatic, subducted material, trapped sea brine, degassing of the mantle
Where in the US is the highest enhances geothermal potential? Why? How is metamorphism involved?
West (yellowstone)
Dynamic Metamorphism
deviatoric stress in dominant, deformation and recrystallization are the main process
Thermal metamorphism
temperature in a near static stress field
Dynamothermal metamorphism
both temp and deformation
Hydrothermal Metamorphism
hot water rich fluids, usually involves metasomatism
Fault-zone metamorphism
high rates of deformation and strain, minor recrystallization inpact/shock
Prograde metamorphism
increase in metamorphic grade with time
retrograde metamorphism
decreasing grade as rock cools
What governs the size and shape of contact aureole formed around a pluton?
Nature of the pluton and nature of the country rock
Nature of the pluton examples
size, shape, orientation, temp, composition
Nature of country rock examples
composition, depth, metamorphic, grade prior to intrusion, permiability
What two rocks can be formed in fault-zones? Which one is found deep and which one shallow?
Fault breccia forms at shallow
Mylonite forms deep
What pressure-temperature conditions are Ophiolite soles formed in
Low pressure, low medium temp
What pressure-temperature conditions are magmatic arcs formed in
low pressure, high temp
What pressure-temperature conditions are continental rifts formed in
High pressure, High temp
What pressure-temperature conditions are Craton formed in
High pressure, low temp (within the subduction zone range)
What pressure-temperature conditions are seafloor formed in
low pressure, low to high temp
What pressure-temperature conditions are subduction zones formed in
High pressure, low temperature
The type of protolith involved in a metamorphic event is best grouped based on what characteristics?
composition
what are some of the common physical weathering processes?
Frost wedging, glaciation, joint-sheeting, root wedging, salt wedging
What are some common chemical weathering processes
dissolution, hydrolysis, oxidation, hydration
What are the products of mechanical weathering
detrital sedimentary rocks
what are the products of chemical weathering
chemical sedimentary rocks
What minerals have a high mechanical preservation potential
quartz, k-spar, plagio, muscovite, protoliths
what minerals have a high chemical preservation potential
iron oxides, quartz, aluminum oxides
What features in grains and lithic fragments in sedimentary rocks are used to narrow down the
possible source area (provenance) of detritus?
size (bigger = closer)
sorting (poorly = closer)
roundness (angular = closer)
What is a paleosol and why are they important?
Ancient soil that can be used to identify geologic contacts and history
What is provenance?
Source terrain for sediments
What is a stromatolite?
Structure found in carbonate rock of large laminated microbial accumulations
What are the two major categories of sandstone?
Arkose and arenite
What is the difference between cement and matrix?
Both are binding agents but a matrix is always made of mud-shaped grains, cement can be bigger
What is the Barrovian Trend
chlorite ->biotite->garnet->staurolite->kyanite->sillimanite
What is the Buchan Trend
Chlorite->biotite->cordierite->andalusite->sillimanite
How are isograds defined
represents the first appearance of a particular metamorphic index mineral as you progress up the metamorphic grade
what is an index mineral
a mineral that forms under specific pressure and temperature conditions that provide info on metamorphic history
Contact Metamorphism
hot magma/liquid touches country rock, deforming it
Regional Metamorphism
large scale tectonic events that cause widespread metamorphism
