GEOL 333, 333
continental margins
where continental landmasses meet ocean
basalt and gabbro
45-55 % silica Ca rich plagioclase, pyrocene, minor olivine dark, dense, most common rocks of oceanic crust
andesite, diorite
55-65% silica Ca/Na rich plagioclase, some mafics, minor quartz, lighter color than mafic
arenite
<5% matrix
wacke
>5% matrix
silicic igneous granite and granodiorite rhyolite and dacite
>65% silica K feldspar, quartz, Na rich plagioclase, muscavite, minor mafic silicates (biotite, amphibole) split into 2 subcategories
pressure increases, metamorphic grade ____
increases
temp increases, met grade ____, speed of met rxns ____
increases, increases
what prevents rock from melting at 40-50 km depth
increasing depth means increasing pressure, which increases melting temperature of rock
andean type
inner wall of trench consists of accretionary wedge, where get complex deformation and high pressure-low temperature metamorphism ~undeformed forearc basin, comprised of clastics shed from volcanic arc Behind arc= fold and thrust belt, grades to undeformed crust narrow or absent continental shelves
formation of komatiite high geothermal gradient
komatiite (fine grained ultramafic igneous rock) due to VERY hot lava flows ONLY in early precambrian. Due to VERY high geothermal gradient early in earths histoyr
volcano hazards - lahar (mudflow)
lahar is mixture of water, volcanic debris that flows down river valleys water from melted snow, ice on mountain slope, or from eruption, or from rain. Mt. Fuji, japan
regional metamorphism
large zones of met caused by HIGH T HIGH P, deep burial
volcano hazards - effect on climate change
large, explosive ashfall eruptions can cause global cooling of up to several degrees for 1-2 years after eruption. climate change can cause crop failure and famine cooling due to SO4 gas coated airborne volcanic ash, which reflects sunlight
permeability from grain size
larger grains = MORE
time
more time = thicker
oceanic basalts include mid ocean ridge basalt
most abundant volcanic Produced at divergent boundaries by decompression melting from relatively shallow mantle source
peridotite
most common ultramafic rock dark, dense, 40-100% olivine, coarse grained. occurs at earths surface only when erosion removed overlying rock
sedimentary
most form by hardening(lithification) of layers of sediment(loose grains of preexisting rock) deposited at earths surface. can also form by chemical or biological precipitation(dissolved ions extracted from water to form minerals) typical feature= layering, horizontal bands formed by settling of grains. typical texture= compacted(clastic) and cemented(grains compressed together)
how do rocks melt?
most rocks consist of >1 mineral, which have different melting temperatures depending on strength of bonds also single minerals melt over ranges of temperatures
Lahar (mudflow)
move quickly or slowly, depending on water content. fast lahars can be lethal lahar from Nevada del Ruiz eruption in Columbia, South America in 1985 killed 25,000
divergent (what it creates)
moving apart oceanic ridge undersea volcanic mountains rift valley oceanic crust produced non explosive lava flows (pillow basalt) crustal rifting normal faults ridge valley volc mountains pillow basalt rifting normal faults
andean type
much of rising magma does not reach surface, forms intrusive bodies large granite batholiths igneous activity results in metamorphism of crustal rocks
oceans are geologically young because when they get old they subduct
must look at rocks on continents to see further back in earth history. some parts of geologic past (especially very old events) can be difficult or impossible to unravel because evidence (rocks) has been obscured, buried, or destroyed
contact metamorphism
next to hot igneous intrusion near surface
divergent rock types
non explosive basalt/pillow basalt
rhyolite granite
occur exclusively on continents (controversial, poorly understood) vast areas of granite usually associated with subduction zones, smaller amounts at hot spots on continents
growth of continents accretion
occurs as colliding island arcs or microcontinents get sutured (accreted) onto main continent. these pieces (exotic/accreted terranes) formed elsewhere, were added to continents age and rock types in exotic terrane are usually different from those that surround it bounded by faults
evidence for plate tectonic theory
ocean basins provide most direct evidence, but oceans are geologically very young and provide data for only 4% of earth history
ocean island basalt
ocean island basalts form by decompression melting over hot spots(zone of localized upwelling mantle within tectonic plate) over oceanic crust Ocean island basalts contain higher amounts of Na, K, Al reflecting deeper mantle source
Andean Type (active) Margin
ocean/continent convergence, oceanic lithosphere is subducted
Japan Type (Back arc)
ocean/ocean convergence, older (denser) oceanic plate is subducted
mid ocean ridge basalt
oceanic crust consists of 200 m of mud(clay, carbonate or silica; thinner at ridge, thicker with ↑ distance from ridge) Underlain by 2 km of basalt (pillow basalt due to underwater eruption, rapid cooling. pillows crack open from erupting basalt, ooze out, form another pillow. sheeted dikes feed erupted pillow basalt) Basalt underlain by 5-6 km of gabbro(slow cooling of mafic magma) below ocean crust is mantle= ultramafic peridiotite
Atlantic Type (passive)
present on both sides of atlantic ocean develops as continents rift apart to form new ocean basin
lithostatic pressure
pressure applied equally on all sides, causes DECREASED pore space
hot spot on continent
(columbia river basalt) from deep mantle continental basalts
new rift zone
(east africa rift, rio grande rift) from deep mantle sources. continental basalts
atlantic type
-broad continental shelf underlain by thick sequence of marine sediments(clastic, carbonate) -below are remnants of rifting stage -nonmarine sediments, evaporites, basalt lava, normal faults
continental collision characteristics
-continental crust and island arc are buoyant, unable to be subducted -down going slab breaks off, remelts, volcanism eventually ceases -continents welded together in suture zone(former trench location) -intense deformation, fold and thrust belts on both sides of volcanic arc -crustal thickening (mountain belt) from underthrusting of one continent beneath other (formation of metamorphic rocks) -shallow major earthquakes and minor EQ
divergent plate boundary - normal wall
-hanging wall moves down relative to footwall -created by crustal extension (pulling apart) associated with divergent plate boundaries (simplified diagram below)
evolution of divergent plate boundary
-initial stage: rifting(splitting continental plate -continent splits (some oceanic crust forms) -abundant ocean crust forms
north american craton
-precambrian basement(granitic plutons, metamorphic rocks) great uncomformity meaning? -paleozoic (and mesozoic) sedimentary rocks- gently deformed into series of basins and domes -cratonic basins have sedimentary rock deposited in shallow epicontinental seas when oceans covered large areas of continents -rocks record many marine transgressions (high sea level, continents flooded) and regressions
importance of igneous rocks
-understand Earth's geologic and tectonic history -nature of earths layers -Radiometric age determinations -Rock paleomagnetism -rock cycle(weathered and metamorphosed igneous rocks)
rocks are characterized based on
1. mineral content 2. texture- size (large= coarse grained, small, microscopic=fine grained), shape, arrangement of mineral grains(aligned or random)
what are 2 reasons for difference in viscosity
1. temperature: decrease temp. causes increase viscosity. silicic lava usually much lower temp than mafic 2. silica content: increase silica content causes increase viscosity due to increase linking of silica tetrahedra in silicic lava
volcano hazards - effect on climate
1816 is Year Without a Summer due to massive eruption of Mt. Tambora in Indonesia in 1815 estimated 90,000 deaths world wide from famine
lake nyos (1986)
CO2 gas from magma seeped upward, dissolved in bottom of deep lake lake overturned and huge amount of CO2 gas released heavy gas moved downslope, displaced O2 in low areas
DECREASED grain size = ____ K
DECREASED large, well connected pore spaces (like gravel) - high K
DECREASED sorting _____ n and K
DECREASES
INCREASED lithification _____ n and k
DECREASES
all three have
GEOLOGIC HISTORY
importance of sed rocks
GEOLOGIC HISTORY RESOURCES CIVIL ENGINEERING HAZARDS LANDSCAPE surface bedrock energy 8 THINGS
importance of ig rocks
GEOLOGIC HISTORY nature of earths layers radiometric age determination rock paleomagnetism rock cycle 5 THINGS
silicic
HIGHEST VISCOSITY flows slowest lowest melting point EXPLOSIVE
granodiorite
K-spar<plagioclase
ultramafic
LEAST VISCOUS flows EASIEST highest melting pt nonexplosive
glacial till porosity and K
LOW has sand and mud grains filling pores
composition of igneous rocks
O, Si, Al, Fe, Ca, Mg, Na, K, composition plus temperature, pressure, H2O content characterize magma, control what minerals form Many classification schemes, all based on texture (grain size), composition (mineral, chemical or both)
importance of met rocks
RESOURCES ENGINEERING HAZARDS LADSCAPE 4 THINGS
sedimentary and met both have
RESOURCES ENGINEERING HAZARDS LANDSCAPE 4 THINGS
flat slope
SOIL RETENTION INCREASE chemical weathering THICK soil
andean type
abrupt changes to topography, trench to high mountains within 200 km
ocean continent
active andean ocean/continent convergent ocean lithosphere is subducted trench, mountains, accretionary wedge
andean type mountains
active volcanoes of andesitic composition (magmatic or volcanic arc), due to melting associated with down going slab
passive margin
adjacent to seafloor spreading us east coast
importance of soils
agriculture ore deposits ENGINEERING HAZARDS land use decisions GEOLOGIC HISTORY 6 THINGS
decompression melting
also, get drop in pressure when hot rock moves to shallower depths, this can happen at mantle plumes and under oceanic ridges
lithic wacke grain size and shape and sorting matrix or cement minerals dep env
angular matrix made of volcanic minerals convergent plate boundary, orogenic belts, turbidites in accretionary wedge
feldspathic arenite grain size and shape and sorting matrix or cement minerals dep env
angular feldspar <10% poorly sorted k feldspar weathered to kaolinite near rivers
collisions (orogenesis)
as convergent plate boundaries evolve, down going plate eventually carries either island arc or continent to subduction zone Becomes collision zone
ocean/ocean
back arc japan ocean/ocean convergence older oceanic plate is denser and subducted ocean crust surrounds both sides
hot spots
basalt volcanoes can also occur within tectonic plate at hotspot over crust localized zone of upwelling mantle
continental collision ophiolites
before collision, slabs of ocean crust can break from down going slab and get emplaced (obducted) onto continental crust(ophiolites)
hanging wall
blocks of (dipping) fault are classified. they are the ones on top of the fault
importance of weathering
building degradation (acid rain) cool landscapes frost wedging plant roots/burrowing organisms exfoliation/pressure release salt crystal growth in joints abrasion (wind or water) 7 THINGS
volcano hazards - gases
can get harmful gases CO2, SO2, HCl sulfur rich gas emissions
breccia grain size and shape and sorting matrix or cement minerals dep env
coarse angular poor sorted matrix or cement variation of minerals high energy env. w/little transport: landslide, meteorite impact, etc
conglomerate
coarse round poor sorted matrix or cement variation of minerals mountain rivers
fossiliferous limestone grain size and shape and sorting matrix or cement minerals dep env
coarse grained calcite cement made of calcite tropical reef
granite
coarse grained k-spar>plagioclase
diorite
coarse grained underlies explosive volcanoes at convergent boundaries
rock definition
coherent, relatively hard, naturally formed mass of mineral matter
accretion
colliding island arcs/microcontinents get sutured onto main continent
texture of igneous rocks- oceanic crust
commonly see fine- grained igneous rocks at surface (fast cooling) underlain by coarse grained igneous rocks from same magma basaltic lavas on top. gabbroic rocks on bottom
sources of underground heat
compression original heat from when earth formed
sedimentary rocks form near earths surface metamorphic rocks form at great depths, molten rock occurs at various depths, forming igneous when cools
continuous burial will typically produce first sedimentary, then metamorphic, then igneous rock. cycle driven by burial and then uplift
andes mountains cascades mountains
convergent plate boundaries
igneous rock is produced from eruptions and igneous intrusions due to melting of down going slab. igneous intrusions cause metamorphism of crust exposed volcanic rock at surface gets weathered to form sediment, which is transported, accumulates into basins on both sides, eventually getting buried to form sedimentary rock. some rock gets subducted and remelted, continuing rock cycle
convergent plate boundary
lithosphere
cool brittle outer layer crust and upper mantle 100 km thick
what is most important factor controlling texture (grain size) of igneous rock?
cooling rate of molten rock because long time to form large mineral grains. Minerals have ordered atomic arrangements with specific composition
gabbro
course grained underlies basalt in oceanic crust
crustal rifting
creates normal faults
hydrothermal alteration
crustal rocks are hydrothermally altered at oceanic ridges Related to hydrothermal vents also created black smokers(hot undersea geysers), chimneys(precipitate of metallic sulfide minerals)
andean type trench
deep linear trough where oceanic plate begins subduction
divergent plate boundary
defined by oceanic ridge(spreading center), undersea volcanic mountains and rift valley. oceanic crust(basalt) produced at ridge due to rising magma(decrease pressure causes melting), cooled rock moves laterally away from ridge. Mantle(low in silica and water) melts, producing non-explosive lava flows(pillow basalt) Minor shallow EQ as magma reaches surface
controls on melting chemical composition
different mixtures of minerals will greatly affect melting temperatures. mixture of plagioclase and quartz melts at much lower temperatures than pure quartz
if water is absent, _____ and _____ are very slow
dissolution and recrystallization
occurrence and origin of basalt, gabbro
divergent plate boundaries, oceanic hot spots mafic igneous rocks are only igneous rocks in oceanic crust source of magma= partial 30% melting of ultramafic mantles
ultramafic igneous rocks Peridotite, Kamatiite
dominated by mafic silicates (olivine, pyroxene), no quartz, little to no feldspar <40% silica
parent rock
easily decomposed rock form deeper soils
extrusive rock glassy texture
environment formation: explosive eruptions or lava flows into air, water, ice
Mt. Pelee Ash flow Case History
eruption in 1902 on caribbean island of martinque destroyed city of St. Pierre, killing 28,000 in 30 seconds
convergent rock types
explosive andesite volcanoes (intermediate to silicic)
volcano hazards ash flow/pyroclastic flow
explosive eruption of huge amount of viscous magma creates mixture of superhot gas and pyroclastic debris that races down mountain side. huge destruction possible
volcano hazards- explosion and ashfall
explosive eruption of plume of volcanic ash (small, abrasive pieces of rock) cab cause crop damage, livestock deaths airplane engine failure
what is cooling history of porphyritic texture
fast and slow cooling. initial slow cooling in subsurface followed by rapid cooling due to eruption of lava and crystals to produce fine-grained matrix.
aphanitic (fine grained)
fast cooling rate fine grained texture- aphanitic extrusive forms at earths surface
mafic igneous rocks weather _____ than silicic ig rock
faster
california type (transform)
fault motion causes abrupt topographic differences between continents and oceans (irregular mixture of basins and ridges as crustal fragments are broken, juxtaposed next to oceanic crust), poorly developed shelf, deep sedimentary basins
mudstone/shale grain size and shape and sorting matrix or cement minerals dep env
fine thin/platey well sorted no matrix kaolinite, smectite, illite, quartz deep water
rhyolite
fine grained
andesite
fine grained convergent plate boundaries, explosive volcanoes
basalt
fine grained forms upper part of oceanic crust (divergent plate boundaries), many islands or continental areas associated with hot spots
bedded chert grain size and shape and sorting matrix or cement minerals dep env
fine grained silica cement made of silica deep ocean
volatiles
flux melting (addition of volatiles) drives partial melting at convergent plate boundaries Sediments and fractured rock associated with subducting oceanic lithosphere bring H2O and CO2 into mantle, which melts partially. once magma is generated it rises because magma is less dense than solid rock
igneous
form by cooling of solidification of hot molten rock. typical texture- interlocking with random arrangement, no space between grains similar to jigsaw puzzle
origin of silicic igneous rock subduction, heat transfer
form by partial melting of rock in lower crust. Rising mafic plumes from subduction accumulate below lower continental crust (underplanting) of intermediate composition. Heat transfer causes crust to melt partially, produces viscous silicic magma. silicic magma rises slowly, usually cools at depth, producing granite. when it reaches surface, rhyolite eruption occur
metamorphic
form when preexisting rock changes (shape or mineral content) due to intense heat and pressure. usually occurs deep below earths surface typical texture= foliated and metamorphic banding
subduction zone
from shallow mantle sources continental basalts
igneous rocks and surface processes studied directly at active or fossil volcanoes. Underground igneous rocks and processes studied by looking at locations where surface rocks have eroded
geologists also use geophysical methods(seismic waves, density), lab studies (experiments at high temperatures...) computer models
temperature increases with increases depth within earth
geothermal gradient
creation of magma- melting
geothermal gradients in upper part of crust range from 25-100 C/km Different tectonic settings have different geothermal gradients; higher at volcanic areas(divergent and convergent plate boundaries, hot spots), lower in cratonic interior, very low in accretionary prism
decompression melting
get drop in pressure when tectonic plates begin to rift (diverge) due to thinning of lithosphere. For solid rock near its melting temperature, sudden drop in pressure causes melting (decompression melting)
obsidian
glassy volcanic rock
porosity in gravel sand and mud
gravel and sand similar, mud HIGHEST
cinders
gravel size pyroclastic debris/glass used in road construction, mulch
transform
grinding past in horizontal motion no mountains or volcanoes EARTHQUAKES right along fault line plates move in same direction along fracture zone san andreas fault bends make localized zones of compression to cause mountain building, or extension to cause crustal thinning, forming basin
ophiolite suite
group of rocks comprising oceanic lithosphere thrust onto land during tectonic plate collisions
normal faults
hanging wall moves down relative to foot wall, created from divergence
reverse fault
hanging wall moves upward relative to footwall created by crustal compression(plates come together) associated with convergent plate boundaries
volcano benefits, geothermal energy
heat from shallow magma used to generate electricity
pumice
highly porous, lightweight volcanic rock used in soap and pencil erasers
Himalayas
himalayas formed with India collided with and thrust under Eurasia continental collision
asthenosphere
hot plastic mantle only represents layer over which tectonic plates move 100-300 km deep
porosity from grain size
if grain shape is constant, NO correlation
volcanic gas hazards - Lake Nyos
in 1986 in Cameroon, Africa, 1,700 died due to volcano derived CO2 gas released quickly from Lake Nyos. People died od asphyxiation when cloud of dense CO2 gas rolled down hillside
decrease in temp causes ____ in viscosity
increase
control on melting - pressure
increase pressure favors denser, more ordered solid phase decrease pressure lowers temperature of boiling water
directed pressure
increased pressure along one direction, not equally, flattens object = FOLIATION
igneous - word origin
latin "ignis" = fire form by cooling and solidification of hot molten rock either at surface or below ground
pore fluid
little present during metamorphisms, but INCREASES rate of chem rxns
creation of new land
loihi seamount Heimaey, iceland
mafic
lower viscosity than silicic flows MORE EASILY
why is basalt more common extrusive igneous rock than rhyolite?
mafic magma has lower viscosity than silicic magma so it flows more easily
controls- magma viscosity
magma movement governed by viscosity (resistance to flow) silicic magma is most viscous (resists flowing) ultramafic magma is least viscous(flows easiest/fastest)
andesite dacite
major occurrence at convergent plate boundaries (subduction zones) pacific ocean margin- Mt. Saint Helens Origin of intermediate igneous rocks = controversial, less understood than mafic rocks
volcano benefits- ore deposits
many metallic ore deposits in roots of old volcanoes
quartz arenite grain size and shape and sorting matrix or cement minerals dep env
medium well rounded well sorted <5% matrix quartz shallow sea, beach, etc
oolitic limestone grain size and shape and sorting matrix or cement minerals dep env
medium grain size calcite cement made of calcite formed around core (or quartz or calcite grain) tropical shelf
texture of igneous rock molten rock
molten rock is amorphous (no crystal structure) due to rapid atomic motion, most chemical bonds are broken
lava
molten rock that flows above ground
magma
molten rock within earth, completely molten fluid mixture of liquid, solid crystals, dissolved gases
which sources of underground heat were greater in precambrian
original heat from when earth formed (collisions and meteorites) many more meteorites early in earths history Radioactivity. more radioactive isotopes then
origin of intermediate igneous rocks subduction
partial melting of subducting oceanic plate (wet sediments, altered basalt) and overlying mantle. volatiles from subducting slab promote melting(flux melting) of overlying mantle, which sends mafic magma rising As mafic magma moves through continental crust, it incorporates some silicic crust (assimilation), producing intermediate composition rock
divergent
passive atlantic "ill pass on the atlantic" Present on both sides of the Atlantic ocean Divergent
japan type (back arc)
passive margin then small area of oceanic crust(+- spreading center) island arc(from ocean/ocean convergence) is similar to magmatic arc (andesite volcanic mountains, forearc basin, accretionary wedge, trench) but ocean crust surrounds both sides
early in earth history, upper mantle melted partially, lightest elements rose to form crust
process depleted upper manlte in ligh elements, Na, K, Al deeper in mantle, those elements are not depleted. several types of basalt depending on tectonic setting, source of magma in mantle (shallow vs deep)
composition of igneous roks
range from silicic to intermediate, mafic, ultramafic felsic has high Al, K, Na ultramafic has high Ca, Fe, Mg alkalic rocks= low silica, rich in alkali elements. rare
komatiite
rare extrusive ultramafic rock from early precambrian.
craton
relatively old area of continent that has been tectonic-ally stable(little major faulting or folding) for long period of time (for north america since precambrian)
volcanic ash
sand size volcanic glass can be fertile soil
ophiolites
section of oceanic crust ocean crust slabs break down from down going slab, get obducted onto continental crust (ophiolites)
why does silicic magma tend to crystallize underground as granite or granodiorite
silicic magma has higher viscosity than mafic magma so it flows slower
lava flows _____ at lower temps
slower
controls on melting volatiles (water)
small amounts of water<<<< melting temperature of rock Water disrupts atomic bonding, allowing lower temperatures for bond breaking to form liquid called flux melting or addition of volatiles common volatiles include H2O and CO2
dry mineral warm/wet mineral hot/wet
smectite; kaolinite; bauxite
steep slope
soil EROSION DECREASE chemical weathering THIN SOIL
evolution of divergent
splitting continental plate, then some oceanic crust forms, then abundant ocean crust forms
melting and crystallization at atomic level
starting with crystalline solid, increase heat causes increase atomic vibrations, eventually results in breaking atomic bonds of crystalline solid so atoms can vibrate more freely. results in liquid magma with no crystalline structure cooling of hot, molten magma causes decrease atomic vibrations, eventually allows atomic bonds to form and minerals to grow
California Type (Transform) Margin
strike slip faulting southern california
active margin
subduction and volcanism us west coast
convergent
subduction zone oceanic crust destroyed oceanic trench mountain belt w/explosive andesite volcanoes continental collisions fold thrust belt suture shallow earthquakes ophiolites accretion
controls on melting
temperature increase= 25 C/km, yet most of mantle is solid
terranes in eastern north america
terranes were accreted to eastern north america during Paleozoic
terranes in western north america
terranes were accreted to western north america during Mesozoic/Ceozoic
foot wall
the ones below the fault
hot and wet = desert and polar =
thick; thin
accretionary wedge
thrust faulted, folded marine sediment, scraped off downgoing slab
volcano benefits
tourism national parks and monuments
strike slip
transform california strike-slip faulting topographic differences between continents and oceans, poorly developed shelf, deep sedimentary basins
san andreas fault
transform plate boundary
volcano hazards- lava flows
usually non lethal, but can cause considerable damage
glassy
very fast cooling rate amorphous grain size glassy texture obsidian, pumice
coarse grained (phaneritic)
very slow cooling rate coarse grained phaneritic texture intrusive deep in earth
very coarse grained (pegmatitic)
very slow, abundant H2O cooling rate very coarse grain size pegmatitic texture
volcano hazards tsunami
volcanic eruptions rarely create tsunamis Krakatoa eruption created very large tsunami, killed 36,000
permeability from sorting
well sorted = MORE
porosity from sorting
well sorted=HIGH poor sorted = LOW
transform plate boundary
where two plates grind past each other with horizontal motion defined by major fault (transform fault) No creating or destroying crust, no mountains or volcanoes Earthquakes (major and minor)