Geology 101 Quiz 4 Flashcards
knowledge of rock properties can help determine things like
where it is dangerous to build, whether a groundwater contaminant will migrate off site, what is the best material for making buildings or highways
understanding earth processes can help determine things like
where to expect earthquakes, where to dig for gold or oil, how to make synthetic rubies and diamonds, why a lake in Africa discharged a CO2 cloud that killed hundreds
three basic rock types
igneous, sedimentary, metamorphic
igneous rocks
formed by solidification from magma
sedimentary rocks
formed by accumulation and lithification of existing mineral grains OR precipitation of dissolved ions from water
metamorphic rocks
formed by alteration of existing rocks under high temperature and/or pressure
lithification
the process of turning sediments into rock
weathering
physical breakage and chemical decomposition of rocks (including dissolution)
erosion
transport of weathered rock away from point of origin
rock cycle
rocks are generally thought of as eternal; rocks can be “recycled,” where one rock can be broken down or altered and turned into a different type of rock
igneous rock -?-> weather erode
uplift
weather erode -?-> sedimentary
deposition, burial, lithification
sedimentary -?-> weather erode
uplift
sedimentary -?-> metamorphic
heat pressure
metamorphic -?-> weather erode
uplift
metamorphic -?-> igneous
melt, cool, solidify
igneous -?-> metamorphic
heat, pressure
sedimentary cannot go straight to ? and why
igneous; a sedimentary rock will form a metamorphic rock prior to melting
?, or texture of an igneous rock, was used to classify igneous rocks before it was really understood why it varied so much
crystal size
the primary clues to what causes crystal size to vary in igneous rocks came from studying ?
volcanic lava flows (since the flows started as magma and solidified to form igneous rocks)
if a section of cooled lava was broken open, several observations could be made:
large crystals are never observed in lava; of the small crystals present, the larger crystals are always found near the base or middle, never at the top
what suggested that time must play a role in igneous rock crystal size?
the top of the lava flow cools the fastest and the interior cools slowly
igneous rocks: the slower the cooling rate, the more time atoms have to ?
align themselves to grow larger crystals
since lava flows always produce small crystals, igneous rocks with large crystals must have formed where?
beneath the surface where cooling rates could be very slow
the presence of ? in magma also facilitates larger crystal growth
water
two categories of igneous rocks
intrusive, extrusive
intrusive igneous rock
magma intruded into existing rock and solidified beneath the surface
extrusive igneous rock
magma extruded to the surface (lava) and solidified on the ground
igneous rocks are classified using two different systems based on either ? or ?
the occurrence of the rock (where found and in what form) or the composition of the rock (what minerals it is made from)
pluton
large igneous body formed at depth
batholith
large pluton
stock
smaller pluton
plutons form in different ways, but all ways start with
magma that begins to rise (because it is less dense than solid rock)
the simplest way a pluton forms is by simply
melting its way upward
a pluton may also form by stressing ?
overlying rock and flowing upward into fractures
sill
tabular intrusion between existing layers
sills usually form (horizontally/vertically) because most layers are (horizontal/vertical)
horizontally; horizontal
dike
roughly planer intrusion that cuts across existing layers
sills are also known as
concordant intrusives
dikes are also known as
discordant intrusives
vein
deposit of foreign minerals within a fracture; can be igneous or sedimentary
if minerals precipitate out in a fracture from water heated by a magma body, the vein is considered ?
igneous
if minerals precipitate out in a fracture at lower temperatures not associated with magma, the vein is considered ?
sedimentary
examples of massive, uplifted batholiths
Yosemite National Park, California and The Sierra Nevada Mountains in California
examples of a stock, possibly beneath an ancient volcano
Devil’s Tower, Wyoming and Ship Rock, New Mexico
how can we tell if the vein or dike was there first?
if the veins cut through the dike, the dike was there first
extrusive igneous rocks are divided into two categories
lava and pyroclastic material (tephra)
lava
magma that flows over the surface of the ground and solidifies
pyroclastic material (aka tephra)
magma and solidified fragments thrown into the air during an explosive eruption
if magma intruded between two existing layers, the upper layer should show
some signs of alteration (metamorphism)
if the crystals in the igneous rock are small and there is no metamorphism,
ancient lava flow
if the crystals in the igneous rock are large and there is metamorphism,
it must be a sill
8 minerals divided into 2 groups
felsic and mafic
felsic minerals
high silica content (SiO2), which makes them less dense, and often lighter in color
mafic minerals
low in silica, higher in Fe & Mg, which makes them more dense, and often darker in color
mafic minerals are more abundant in (continental/oceanic) crust
oceanic
mafic minerals (list)
olivine, pyroxene, amphibole, Ca-rich plagioclase
felsic minerals (list)
quartz, muscovite, potassium feldspar, biotite, amphibole
? is both mafic and felsic
amphibole
granite is (intrusive/extrusive)
intrusive
rhyolite is (intrusive/extrusive)
extrusive
diorite is (intrusive/extrusive)
intrusive
andesite is (intrusive/extrusive)
extrusive
gabbro is (intrusive/extrusive)
intrusive
basalt is (intrusive/extrusive)
extrusive
peridotite is (intrusive/extrusive)
intrusive
komatiite is (intrusive/extrusive)
extrusive
granite and rhyolite are
felsic
diorite and andesite are
intermediate
gabbro and basalt are
mafic
peridotite and komatiite are
ultra-mafic
Magma rising through oceanic crust will tend to be made of ?
mafic minerals
Magma rising through continental crust will tend to be ? if not much continental crust is melted
mixed
Magma that melts lots of continental crust will tend to be ?
felsic
volcanic glass
extrusive igneous rocks; occur when magma cools very fast and the resulting rock has no crystals
obsidian
volcanic glass with no air bubbles
pumice
volcanic glass with lots of air bubbles, called vesicles
tuff
pyroclastic material fused into a solid rock
volcanic ash
dust size tephra
porphyry
a rock with large crystals (called phenocrysts) in a matrix of fine grained crystals
mafic minerals generally melt at (lower/higher) temperatures than felsic minterals
higher
at higher pressure, (lower/higher) temperatures are needed to melt the rock
higher
if water is present, the rock will melt at a (lower/higher) temperature
lower
Bowen’s Reaction Series refers to
the sequence of minerals that crystallize from a magma as it cools, and reactions that take place along the way
discontinuous reaction series
the stepwise reaction sequence pathway (olivine to biotite)
continuous reaction series
the gradual transition from Ca to Na rich plagioclase
