EXAM 3 MATERIAL Flashcards
describe hypabyssal rocks and what they are.
- form near the surface
- cool relatively quickly
- fine grained
describe plutonic rocks and what they are.
- form at depth
- cool slowly
- coarse grained/visible crystals
why do magmas form?
they form when rock is melted
why do magmas ascend upwards?
they are less dense than the surrounding country rock
how is modal rock analysis used?
used for the IUGS classification of igneous rocks
what is mineralological classification?
classifying rocks based on they mineralogical composition
what is the chemical composition classsification?
classifying rocks based on their chemical composition
describe the difficulty of obtaining modal analysis from the different rock types
- coarse-grained plutonic is easy
- fine-grained volcanic is difficult
- glassy rocks is impossible
how are igneous rocks classified?
- mode of occurrence
- mineralogical makeup
- chemical composition
what is the problem with historic classification?
contains a huge number of rock names, not used consistently
what method is used to classify very fine-grained/glassy rocks?
chemical analysis
what is latent heat of fusion?
the amount of energy that must be applied to a rock to melt it.
what role does latent heat of fusion play in melting?
prevents large scale melting in the earth
what are discordant intrusive magma bodies?
if the intrusive body cuts through the surrounding rock, it is discordant
what are Cordant intrusive magma bodies
if the intrusive body parallels the surrounding rock, it is Concordant
in what direction do magmas always intrude?
the minimum stress direction
what are dikes?
a vertical intrusive igenous body
what are sills?
a horizontal intrusive igneous body
what types of igneous intrusions are associated with crustal extension?
dikes and flood basalts
what types of igneous intrusions are associated with crustal compression?
plutons, sills
are intrusive dikes common at any of the plate boundaries?
YES
what are chilled margins?
edges of an igneous intrusion where magma cool rapidly due to contact with colder surrounding rock
how do chilled margins form?
magma cools rapidly due to contact with colder surrounding rock
what are cone sheets?
when pressure increases fractures propagate from the top of the magma chamber to the surface magma seeps in, creating cone sheets
what are ring dikes
when pressure decreases, the roof sinks into the chamber, magma wells up into the fracture
how are ring dikes/cone sheets associated with calderas?
ring fractures penetrate through to earths surface
what are diatremes?
elongate bodies filled with broken breccia fragments.
how do diatremes form?
magma rises quickly, surrounding rock fragments into magma plume
what characteristics are diatremes associated with?
explosive volcanism
do diatremes have any particular mineral components?
YES
- diamond bearing rock
- mg rich mica phlogopite (RARE)
how do diatremes relate to a maars?
maars are the surface expression of diatremes
what are lopoliths?
large, saucer-shaped intrusions having
diameters of up to hundreds of kilometers
at what scale do lopoliths occur at?
massive scale (hundreds of kms)
what is the largest known lopolith and its dimensions?
the bushveld complex
- diameter of 300 km
- thickness of 8km
how was the Sudbury Ontario lopolith triggered?
a large meteorite impact
what are batholiths?
large scale bodies of granitic rock that have large exposures on the surface of the earth
What is the composition of a flood basalt
basaltic lava
what is the composition of a batholith?
ALWAYS granite
how do batholiths form?
magma intrusion and subsequent cooling
are there any important batholiths in north America?
yes, Yosemite is made of mostly batholiths
What controls the shape of lava bodies once they reach the surface?
the body is controlled by viscosity
what are pyroclastic materials?
clastic rocks composed of rock fragments ejected by explosive volcanism
how are pyroclastic materials classified?
-size
-composition
Volcanic Explosivity Index, range, what is it describing, what factors are important in classification?
what is volcanic explosivity based on?
- the volume of tephra produced
- height of the eruption column
Why do we know so much about the eruption of mt vesuvius?
pliny the younger eye witness accounts
when was the eruption of mt Vesuvius?
79 AD
what are flood basalts?
eruptions of basaltic lava pouring from long fissures
how do flood basalts form?
large mentle plume upwells, associated with the breakup of tectonic plates
what tectonic processes are flood basalts associated with?
breakup of tectonic plates (divergent boundaries)
are shield volcanoes associated with flood basalt processes?
YES
are flood basalts associated with mass extinction events?
YES
do composite volcanoes typically produce lava flows?
yes
what are the decan traps?
large flood basalt province in indai
what are the Siberian traps?
large flood basalt province in siberia
what are columnar joints?
sections of flood basalts that propagate into the flow from upper and lower bounds
how are volcanoes classified?
- shape of volcanic structures they form
what is the VEI
volcanic explosivity index
what does the VEI tell us?
quantifies the explosive power of volcanic eruptions
how does viscosity relate to eruption magnitude?
- High viscosity:
- slower moving lava
- more gas bubbles
- more explosive
what is tephra?
fragmental pyroclastic material expunged by volcanic explosion
what are the size denominations of pyroclastic materials and their names?
> 64 mm diameter= bombs
63-2mm diameter= lapilli
2mm or less=ash
how do spatter cones develop?
blobs accumulating around volcanic events
how is volcanic structure shape determined?
- Whether eruptions come from central vents or long fissures
- Explosivity
what makes composite volcanoes composite?
they alternate between pyroclastic and lava eruption, forming stratified deposits
what is the transport mechanism of pyroclastic debris
debris combines with water to form volcanic mud flows called lahars
V HAZARDOUS
how do composite volcanoes differ from other volcanoes?
they produce lava AND pyroclastic material
what are calderas?
volcanoes that collapse when the magma chamber empties
what lava compositions are typical in calderas?
rhyolitic (felsic) lava
any notable calderas in north America?
yes, Yellowstone
what is resurgent doming?
domes that result from caldera eruptions
is resurgent doming seen in Yellowstone?
yes
is resurgent doming seen in valle caldera in los alamos?
yes
describe pyroclastic air fall processes
glowing clouds of hot ash flows
describe epiclastic processes
physical weathering and erosion of preexisting rocks
what are the two types of ash transport from a caldera?
- air fall
- flow
what is air fall ash?
ash ejected high into atmosphere, cools by the time it reaches the surface
what is flow ash?
hot, dense particles moving laterally quickly
what is important to remember about flow ash?
it is moving so quickly there is little time to cool
what are welded tuffs?
material from pyroclastic flow is hot enough to weld back into a single rock
what is the CIPW normative classification?
a method by which chemical analyses of rocks can be recast into common anhydrous minerals.
who developed the CIPW normative classification?
- Washington
- Cross
- Iddings
- Pirsson
Why do CIPW norms predict minerals that many not be present in the mode of a rock
because CIPW does not calculate hyrdous minerals
what are Komatiites
ultramafic lava
why are Komatiites important?
- give insight into early earths deep mantle billions of years ago
- economic importance because of the nickel, copper and platinum elemental occurrences.
what are Komatiites composition?
Lherzolite BUT the texture is consistent with lava flows
What is a TAS diagram useful for?
determining total alkali/silica content when volcanic rocks are too fine grained for modal analysis
is the TAS diagram a useful way of classification?
YES
how does the Irvine-Baragar Classification of Volcanic Rocks work?
uses genetically related rocks and divides them into three main series for classification
is the Irvine-Baragar classification of volcanic rocks popular?
yes
what are the three main series of the Irvine-baragar classification?
- alkaline
- subalkaline
- peralkaline
what are the characteristics of the Alkaline series?
- high alkali content
- silica content
what are the groups the Alkaline series is subdivided into?
- Alkali olivine basalt
- nephelinitic-leucitic-anaclitic
what are the groups the Subalkaline series is subdivided into?
- Tholeiites
- Calcalkaline
what is the difference between Tholeiites
Calcalkaline
- Tholeiites are more iron rich
- calcalkaline are richer in aluminum
what are Ophiolites?
slivers of oceanic crust have been thrust onto continental margins
how do Ophiolites form?
result of obduction
what are ophiolites associated with?
three rock types are associated with the MORs
what is the economic importance of divergent margins?
ore deposit formation
what is the ocean island life cycle (simple)
- active magma rises to create seamount
- magma chamber cools to form a pluton
- seamount weight makes seafloor sink
what are large igneous provinces? (LIP)
large scale flood basalts and their associated features (feeder dikes)
do LIPs have any particular characteristics?
large area occurrence
what are Aulacogens?
a failed third arm in a triple junction
where is most volcanism seen in rock factories
M.O.R
where is the least volcanism seen in rock factories?
cratons
why is the Sudbury lopolith important?
it resulted from an meteorite impact
what conditions are most closely associated with glaucophane?
- HIGH pressure
- LOW temperature
what are the metamorphic facies associated with glaucophane
blueschist facies
what is univariance in a three phase diagram?
all three coexisting phases are in equilibrium with each other
what is divariance in a three phase diagram?
two independent variables that can vary while maintaining equilibrium among three phases.
what is invariance in a three phase diagram?
no independent variables can vary freely and are constrained by equilibrium
what is metamorphism?
the sum of all changes that take place in a rock
what is a protolith
the original rock before it was metamorphosed
what are protoliths of the most common types of metamorphic rock
shale-slate-phyllite-schist-gneiss
what is a prograde reaction
changes that occur while temperature and/or pressure is INCREASING
what is a retrograde reaction
changes that occur while temperature and/or pressure is DECREASING
do retrograde reactions always occur?
why or why not?
NO
what is the distinction between diagenesis and metamorphism
diagenesis are changes that take place in LOW temperature.
(metamorphism in high temp.)
is melting a part of metamorphic reactions?
YES
what is contact metamorphism?
magma intrudes in thermal aureoles, heats and subsequently changes rocks.
how quick are metamorphic reactions?
slow
how do fluids play a role in metamorphic reactions?
yes
what is the biggest contributor to driving metamorphic reactions
Gibbs free energy
describe the principal stress orientations
- can be in opposite directions
- they can be all equal OR all different
what are the three stress motions that can be applied?
- compressive
- tensional
- shearing
how do metamorphic foliations develop?
perpendicular to the maximum compressive stress
what is Metasomatism?
fluids present can remove or add new elements, changing composition
Are rocks efficient at diffusing heat?
NO
what is thermal diffusivity?
the ability of a material to conduct thermal energy
what is regional metamorphism?
minerals with platy shapes rotate into orientations normal to the direction of stress.
!! CREATES FOLIATION !!
what tectonic setting is associated with regional metamorphism?
convergent margins
How are deeply buried and metamorphosed rocks exposed at the surface
they are uplifted and exhumed
does crust thickening play a role in regional metamorphism?
YES
what controls reaction rates in short range metamorphism?
diffusion
what controls reaction rates in long order metamorphism?
fluid transport (Darcy’s law!)
do subducted fluids play a role in regional metamorphism?
YES
how is it possible to identify a protolith based on a metamorphic rock?
bulk chemical composition
what is the most important thing in defining metamorphic grade?
mineral assemblages
what is the difference between shale and schist?
SHALE contains 5% water
what happens to water content during metamorphism?
water is liberated
what is metamorphic grade?
expresses the intrensity of metamorphism
(inc grade=inc temp
what must happen to Gibbs free energy for equilibrium to occur?
GFE is zero
what direction does a metamorphic reaction move to?
reaction moves only in the direction that lowers GFE
what are isograds?
the boundaries between index mineral zones
how important is temp v. pressure during metamorphism
VERY
what are index minerals?
minerals that represent specific equilibrium conditions
what are components?
the minimum number of constituents needed to describe the phases present
what are phases?
individual minerals, liquids and gases
what are degrees of freedom?
how many variables can be changed without changing the phases present.
what do iso-grads represent in regional metamorphism?
LOOSLEY represent metamorphic intensity
how does recrystallization effect Gibbs-Free-Energy?
recrystallization results in a coarser mineral grain, decreasing the free energy
what are the three groups of facies defined by Eskola?
- LOW P. HIGH T
- INC P. INC T (regional orogenic belts)
- HIGH P. LOW T
who developed the concept of metamorphic facies and first recognized 3 groups of facies?
Pentti Elias Eskola
what are geothermometers and what are they used for?
small number of metamorphic reactions very sensitive to changes in temperature.
!! composition is used to determine metamorphic temperature !!
what are geobarometers?
small number of metamorphic reactions very sensitive to changes in pressure.
!! composition is used to determine metamorphic pressure !!
how are metamorphic facies determined?
by studying the ENTIRE mineral assemblage, not a single index mineral.
what is boudinage?
series of resisted deformation (string like sausages)
what is pressure solution?
fluids formed due to melting of minerals at grain-to-grain contacts
what are porphroblasts?
large mineral crystals in metamorphic rock grown within finer grained ground mass.
what is porphoblastic texture?
large single crystals in a fine grained matrix
what is porphoclastic texture?
rocks containing large relict minerals
what is brittle/ductile transition in the crust?
the transition from upper, brittle crust to lower, ductile crust
where does the brittle-ductile transition happen?
10-15 km
what are pelites/pelitic rocks?
rocks containing an abundance of clay minerals
what are petrogenetic grids?
lines that set limits on pressure and temperature ranges over which mineral assemblage could be formed
how are petrogenetic grids useful?
they allow use to set limits for temperature and pressure during formation
are there limits to petrogenetic grids’ usage?
YES
- cannot determine many of the minerals present in metapelites
what are tie-lines representing in petrogenetic grids?
indicate stable minerals
can tie lines in petrogenetic grids change?
YES
can vary depending on bulk composition
what are tie line in Thompson projections?
they represent equant reactions
what are Thompson projections?
tie lines join coexisting phases for just one possible mineral assemblage
what are migmatites?
igneous/metamorphic rock mixed together
how do migmatites form?
high temperatures cause metamorphic rocks to melt.
what is the geothermometer GARB?
geothermometer for coexisting garnet and biotite
what is the geothermometer GARB dominated by?
GARNET AND BIOTITE
how accurate is the geothermometer GARB?
+- 50 DEGREES
what is the geobarometer GRAIL?
reaction of:
Alamandine+Rutile=illimenite+Kyanite+quartz
how accurate is the geobarometer GRAIL?
within 0.05 GPa
STUDY
prograde-retrograde trajectories
hydrothermal processes at divergent margins
- hydrothermal alteration
- most new rock is produced at M.O.R
