Igneous Processes and Volcanism 2/10/14 11:12 AM-Ignous rock’s texture is linked to rate and therefore place of cooling.

Slow cooling of magma in interior allows time for growth of large, coarse crystals, characterizing intrusive igneous rocks.

Intrusive igneous rock is one that forced its way into surrounding rock.

o Surrounding rock called country rock. o Porphyry- an igneous rock that has a mixed structure,

crystals float in mostly fine-grain matrix. Large crystals called phenocrysts form while magma is

below Earth’s surface. Extrusive Igneous Rocks- Form when lava erupts from volcanoes.

o AKA Volcanic rocks. o Lavas- Volcanic rocks formed from lava vary from smooth to

spiky. o Pyroclasts- Rocks made from fragments of lava thrown high

in air -Felsic Rocks- Poor in iron and magnesium, rich in silica high minerals (Quartz).

Tend to be light in color. Granite- One of the most abundant intrusive igneous rocks. Rhyolite- Extrusive equivalent of granite, much more fine-grained.

-Intermediate Igneous Rocks- Midway between felsic and mafic rocks. Minerals of medium amount of silica (plagioclase). Granodiorite and diorite.

-Mafic Rocks- Contain large proportions of minerals poor in silica but rich in magnesium and iron.

Dark colors. Gabbro- intrusive example, coarse-grained,

Basalt- Extrusive Equivalent-Ultramafic rocks- Consist of mafic minerals with barely any feldspar.

Peridotite example. o Dominant in earth mantle.

Rarely found as extrusive because they form at high temperature and are rarely liquid.

-Viscosity- Measure of liquid’s resistance to flow. Increases as silica increases.

-Partial melting- Rock does not melt completely at given temp, because minerals melt at different temps.-Pressure increases with depth, and higher pressure=higher temp required to melt.

Decompression melting- Melting as material rises due to pressure decreasing, without introduction of heat.

o Produces greatest volume of magma.-Water varies melting as well, by lowering the melting temperature.-Large pools of molten rock forms magma chamber- magma filled cavities in lithosphere that form as rising pools of magma push aside other rocks.-Magmatic differentiation- Process by which rocks of diff. composition can arise from uniform parent magma.

Occurs due to different minerals crystallizing at different temps. -Fractional Crystallization- Process by which crystals formed in

cooling magma are segregated from the rest of the liquid.o Crystals formed in magma chamber settles to floor and is

removed from further reaction to liquid. Magma migrates to diff. location, forming new chambers.

Thus crystals are segregated. Magmatic differentiation can be achieved by partial melting over a

range of temps and water content. Magmas do not cool uniformly. Diff temps within chambers may

cause chem. composition to change from one region to another. Some magmas immiscible- do not mix together.

-Plutons- large igneous bodies formed deep in Earth’s crust.-Magmatic stoping- Magma rising through crust makes space for itself in three ways.

Wedging open overlying rock. Breaking off large blocks of rock. Melting surrounding rocks. Batholiths- The largest plutons Stocks- Smallest plutons

-Sill- A sheetlike body formed by injection of magma between parallel layers of bedded rock.

Differ from most lava flows in that o They lack blocky structures characterizing volcanic rocks.o More coarse-grained than volcanics because they have cooled

more slowly.o Rocks above and below sills show effects of heating (color

change).o Many lava flows overlie older flows. Sills do not.

-Dikes- Major route of magma transport in the crust. Like sills in being sheetlike igneous bodies, but dikes cut across

layers in bedded country rock. Often create channels by pressure of rising magma.

-Veins- deposits of minerals found within a rock fracture foreign to the country rock.

Pegmatites- Veins of extremely coarse granite cutting across finer country rock.

-Raw material involved in seafloor spreading is peridotite from asthenosphere.

Melts by decompression melting as plates pull apart. This forms magma chamber beneath mid ocean crest.

o Some magma rises through narrow cracks that open where plates separate and erupts into ocean, forming pillow lavas.

o Some magma freezes in cracks asvertical sheeted dikes.o Remaining magma solidifies as massive intrusions of gabbro

as magma chamber pulled apart by seafloor spread.-Subduction zones as magma factories

Oceanic plate collides and dives beneath other oceanic plate. Fluid-induced melting- Lower melting temp of rock. As lithosphere moves lower, pressure squeezes water out of

minerals causing melting of oceanic crusts. Magma rises and forms volcanic island arc.

-Mantle plumes- Sites of decompression but form within lithospheric plates, not along borders.

Mantle plumes that reach earth’s surface and form hot spots cause outpourings of basalt (produced by decompression melting.)

-Volcano- A magma chamber to which magma is transported from deep within Earth.

Most found at convergent plate boundaries.-Types of Lava

Basaltic Lavao Most common.o Produced along mid-ocean ridges and hotspots in continental

rift valleys. Andesitic Lavas

o More viscous than basaltic lavas.o Erupt mainly in volcanic belts above subduction zones.

Rhyolitic Lavaso Produced in zones where heat from the mantle has melted

large volumes of crust.

-Textures of Volcanic Rocks Obsidian- Glassy rock formed by rapidly cooling silica rich lava. Pumice- Extremely vesicular volcanic rock.

-Pyroclastic deposits When magma rises and pressure drops, volatiles may be released

with explosion, overlaying solidified rock into pyroclasts. Finest fragments called volcanic ash. Blobs of lava solidify into volcanic bombs. Hot sticky pyroclasts weld together. Rocks from small fragments called tuffs. Rocks from larger fragments called breccias. Pyroclastic flows occur when hot ash, dust, and gases ejected in

glowing cloud that rolls downhill at high speeds. -Central eruptions- discharge lava from central vent (pipe coming from magma chamber).

Shield volcano- Formed from copious frequent flows. Broad shield shaped volcano.

o Gentle, lava flows, not as explosive, ocean islands, basaltic silica composition.

Volcanic Domes- Formed from viscous lava producing rounded step sided mass of rock.

Cinder Cones- Formed when volcanic vents discharge pyroclasts, solid fragments form these cinder cones.

Stratovolcano- Formed when volcano blows lava and pyroclasts, building this concave shaped composite volcano.

o Steep, layers of pyroclastic material, andesitic silica composition, explosive, volcanic arcs.

Crater- Bowl shaped pit found at summit of most volcanoes surrounding central vent.

Caldera- Overlying volcanic structure can collapses if magma is rapidly discharged, forming this massive depression.

-Fissure eruptions- Volcanism along mid ocean ridges.

Basaltic silica, mid ocean ridges, not as explosive.o Flood basalts- Flows from fissure eruptions pile up into this. o Ash-flow deposits- Eruptions of pyroclasts on continents have

produced these sheets of volcanic tuffs.-Volcanic disasters

Flank collapse – Big piece of volcano breaks off and slides in landslide.

Caldera collapse Eruption clouds Reduce risk through awareness and public policy.

Sedimentation: Rocks Formed by Surface Processes2/10/14 11:12 AM

Weathering and Surface Processes of Rock Cycle-Sediments and sedimentary rocks formed are produced by weathering and surface processes.-Materials move from source area (created) to sink area (deposited).-Surface processes

-Weathering- General process by which rocks are broken down at surface to produce sediment particles.

o Physical Weathering- Takes place when solid rock is fragmented by mechanical processes (freezing and thawing).

Does not change chemical composition.o Chemical Weathering- Processes by which the minerals in a

rock are chemically altered or dissolved. Erosion- Processes that dislodge particles of rocks caused by

weathering and move them away. Transportation- Processes by which sedimentary particles moved to

sink areas.o Water currents, wind, or moving ice to transport particles.

Deposition (Sedimentation)- Processes by which sediments settle as water and winds slow or glaciers melt.

Burial- Layers of sediment accumulate on top of older layers. Diagenesis- Refers to physical and chemical changes by which

sediments buried in basins are lithified into sedimentary rocks.-Chemical weathering makes each susceptible to fragmentation, physical weathering producers the fragments.

Clastic particles- Range in size. Siliciclastic sediments- Sediments formed from silicate minerals. Chemical sediments- Form at or near place of deposition,

produced by chemical weathering. Biological sediments- Form near place of deposition, result of

mineral precipitation by organisms (shells, skeletons).o Transportation, further breaking, and deposition of these

results in bioclastic sediments. Most sediments transported by air and water currents.

Particle size best indicator of how quickly it will settle. Large particles settle faster than small.

As current slows, biggest particles settle first. Strong currents carry gravel and smaller particles.

o Most common in mountains, erosion rapid. Moderately strong currents lay down sand beds.

o Common in most rivers Weak currents carry muds of finest clastic particles.

o Common at bottom of river valley. As currents slow, deposition occurs in layers called sorting. Salinity- Total amount of dissolved substances in given volume of

water- constant in ocean.Sedimentary Basins- Depressions in crust where sedimentation formed thick accumulations of sediment and sedimentary rocks.

Rift basins- Deep narrow, long, with successions of sedimentary and extrusive and intrusive igneous rocks.

Thermal subsidence basins- Cooling of the lithosphere is the main process creating sedimentary basins.

Sediments from erosion of adjacent land fill the basin nearly to sea level along edge of the continent, creating continental shelf.

Flexural basin- Weight of the overriding in convergent collision causes underlying plate to bend down producing this basin.

Sedimentary environment- Area of sediment deposition characterized by combination of climate conditions and physical , chemical, and biological processes.

Continental environment- sedimentary environments on continents.o Lake environments- include inland body of fresh water.

Transporrt agent, small waves. Chemical sedimentation may occur.

o Alluvial environment- Include the channel of a river, its borders and wetlands, and flat valley floor.

o Desert environment- Arid. Wind and rivers transport sand and dust.

o Glacial environment- Dominated by dynamics of moving masses of ice and characterized by cold climate.

Shoreline sedimentary environments- Dominated by shoreline environments.

o Deltas- where rivers enter lakes and oceans.o Tidal flats- where extensive areas exposed at low tide are

dominate by tide currents.o Beaches- Where strong waves approaching and breaking on

shore distribute sediments. Marine environments

o Continental shelf environment- Located in shallow waters off continental shores. Sedimentation is controlled by gentle currents.

o Organic reefs- Carbonate structures formed by carbonate secreting organisms.

o Continental margin and slope environments- Found in deeper waters off edge of continent.

o Deep sea environments- Found far from continents where waters are deeper than reach of currents.

Siliciclastic sedimentary environments – Dominated by siliciclastic sediments.

Chem and bio sedimentary environments – Characterized chem and bio precipitation.

o Siliceous environments- Unique deep sea sedimentary environments named for remains of silica shells deposited in them.

o Evaporite environments- Created when warm seawater of sea evaporates more rapidly than it can mix with sea water from open ocean.

Sedimentary structures- Include all kinds of features formed at time of deposition.

Sediments characterized by bedding- occurs when layers with different size particles deposit on top of each other.

Cross bedding- Consists of beds deposited by wind or water inclined at angles.

Graded bedding- Most abundant in continental slope and deep-sea sediments.

Ripples- Very small ridges of sand or silt whose long dimension is at right angles to current. Form low narrow ridges.

Bioturbation- Organisms churn and burrow though muds and sands.

Bedding sequences- Built of interbedded and vertically stacked layers.

-Burial- Trapping of of sediments on ocean floor.-Diagenesis- Many physical and chemical changes that result from increasing temps and pressures as buried deeper in crust.

Cementation- Chemical change in which particles are binded together.

o Decreases porosity- percentage of a rock’s volume consisting of open pores between particles.

o Compaction- Decrease in volume and porosity of a sediment. Occurs as particles squeezed closer together by weight

of overlying sediment.o Lithification- Hardening of soft sediment into rock.

Classification of particle size Coarse grained siliciclastic- gravel and conglomerate

o Gravel – coarsest siliciclastic sediment. Particles larger than 2mm.

o Conglomerate- Lithified equivalent of gravel. Medium grained siliciclastics- Sand and sandstone

o Sand- Consists of medium sized particles. .062mm-2mm Can be moved by moderate currents.

o Sandstone- Lithified equivalent of sand. Fine-grained silciclastics- Silt, Siltstone, mud, mudstone, clay,

claystoneo Silt- Most grains between .0039mm-.062mm

Siltstone- lithified equivalent.o Mud- Siliciclastic sediment containing water in which most

particles less than .062mm.

Mudstone- Rock equivalent. Blocky with no bedding. Shale- Composed of silt plus clay.

o Clay- Most abundant component of fine-grained sediments. Less than .0039mm Claystone- Rocks made of clay.

Classification of chem and bio sediments and rocks Carbonate sediments and carbonate rocks- Formed by

accumulation and lithification of carbonate minerals secreted by organisms.

o Most abundant carbonate mineral is calcite. o Reefs- Ridgelike organic structures composed of carbonate

skeletons and shells of millions of organisms.o Dominant sedimentary rock lithified from carbonate

sediments- Limestone.o Dolostone- Made of dolomite which is made of calcium

magnesium carbonate. Evaporite sediments and evaporate rocks- Chemically

precipitated from evaporating seawater (Marine) and lake water (nonmarine)

Natural Resources Coal- Biolgocial sedimentary rock composed of organic carbon

formed by diagenesis of swamp vegetation.

The Carbon Economy 2/10/14 11:12 AMCarbon Economy- Energy system run primarily on fossil fuels.-Fossil Fuels

Natural gas- Simplest hydrocarbon, methane gas. Crude oil- Diverse class of liquids composed of more complex

hidrocarbons. Oil window- Crude oil forms at this limited range of pressure and

temps. Oil trap- Geologic structures that create impermeable barrier to

upward migration.Alternative energy resources

Nuclear energy- Fission of uranium releases heat to make steam to make energy.

o Uranium found in granite. Largest mineral energy resource. Solar energy- Resource cannot be depleted by usage. Hydroelectric energy- derived from moving water. Wind energy- Made with wind turbines. Geothermal energy- Depends on heating of water as it passes hot

rock. Biofuels- Derived from biomass such as ethanol.

Earthquakes 2/10/14 11:12 AMEarthquake- Occurs when brittle rocks under stress suddenly fail along a geologic fault.Elastic rebound theory- Explains why earthquakes recur on active faults

Distance of displacement between blocks of earthquake- fault slip.-Fault Rupture During Earthquakes

Focus- Point at which fault slipping begins Epicenter- The geographic point on Earth’s surface directly above

the focus.-Aftershocks- Smaller earthquakes after main event.-Foreshocks- A small earthquake that occurs before or near the mainshock.-Measuring Earthquakes using Seismic Waves

Seismograph- Instrument that records the seismic waves generated by earthquakes.

P waves- First waves to arriveo Compressional waves- pushpull.o Very fast. Go through all materials.

S waves- Secondary waves follow P waves.o Shear waves- displace at right angleso Half speed of P.o Can’t travel through liquid or gas.

Surface waves- Only waves on earth surface, slower, after P and S waves.

Magnitude scale- Seismograph measurements of earthquakes. Intensity scales- Shows intensity of shaking directly from the

effects of the earthquake. Fault mechanism- Tells us whether rupture is normal, reverse or

strike slip fault.

-Exploring earth’s interior using seismic waves Melting in earth that causes slowness in S-wave velocity is called a

low velocity zone. Seismic topography- Velocities of seismic waves used to sweep

interior in directions to construct three dimensional image of interior.

-Damage from earthquakes Primary hazard is ruptures , subsidence and uplift, and ground

shaking. Secondary hazards are from landslides and other ground failure that

cause movements in earth materials. Seismic hazard- Describes frequency and intensity of shakind and

disruption. Seismic risk- Damage expected in region Building code- Force a structure must withstand.

-Recurrence interval- Time required to accumulate the strain that will be released by fault slip in the future.