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)