Intro to geology

Two types of Ion

cation, anion

Change from Brittle to Ductile

causes S-wave velocity to decrease

Changes in the chemical compositon beween layers

create changes in density

4 layers of Earth

crust, mantle, outer core, inner core

Compound

substance formed by the chemical combination of two or more elements in definite proportions

Resistance is tied to

density of the material

Magma doesn't always form when continental plate meets continental, but if minor subduction occurs

magma can form and will be felsic

Lava

magma that has reached the surface- still molten, not yet solidified to rock

Nonmetalic

-

We can reconstruct the rates and history of plate motion based on:

--hot spots --orientation of magnetic minerals

Amphiboles

-2 non perpendicular cleavage planes at 60 and 120 -2 single chaines liked by oxygens= ouble chain

Ring of Fire

-A major belt of volcanoes that rims the Pacific Ocean -Locations of earthquakes and volcanoes tned to coincide with seafloor topopgraphy

Continental Crust

-has high silica -has low density -Oceanic is thicker

Electrons fill up _____ surrounding the nucleus

energy levels

Ionic Bond

with electrons transferred

Locations where sediments are deposited: Shoreline (where land meets water)

• Medium-energy transport • Medium grain sizes deposited

Convergent plate boundaries

• Oceanic-oceanic → mafic • Oceanic-continental → intermediate to felsic • Continental-continental → felsic (if any)Hot spots

Divergent plate boundaries

• Oceanic-oceanic → mafic, ultramafic• Continental-continental→ felsic, then intermediate, then mafic

organic sedimentary rock

• Organic carbon-rich plant remains are buried relatively fastSwamp plants (~45% carbon)turn into Peat (~50% carbon) turn into Lignite (~70% carbon)turn into Coal • Bituminous (~80% carbon) • Anthracite (~98% carbon; actually a metamorphic rock)

Shale, Claystone

• Sedimentary rocks formed from clay • Cannot see particles with naked eye • generally deposited in quiet waters - lakes, lagoons, swamps or deep ocean bottom - If black, less oxygen in water - If red, more oxygen in water Shale breaks along bedding planes, claystone does not

Magnetic Field Reversals

• The variations of fluid movement in the outer core also make it possible for Earth's magnetic field to spontaneously reverse itself • i.e. magnetic N and magnetic S can be flipped Step 1: Normal orientation Prior to Reversal Step 2: Beginning of magnetic Reversal Step 3

Hot spots

• under oceanic crust → mafic • under continental crust → intermediate to felsic

Chemical sedimentary rocks

●Dolostone ●Ironstone (aka iron formation) ●Evaporite

Biological Sedimentary Rocks

●Limestone (calcite-based) ●Chert (silica-based) ●Organic (organic carbon-based) ●Phosphorite (phosphate-based)

Basaltic lava types:

●aa ● pahoehoe ● pillow Lowest silica content, lowest viscosityCommon at hot spots and mid-ocean ridges

The Breakup of Pangea

- Divergence of North America & Africa, formation of the Atlantic Ocean (Late Triassic) - Divergence of Antarctica, India, and Australia from South America and Africa (Jurassic) - Divergence of South America and Europe. Convergence of Europe and Africa. Divergence of Australia and Antarctica (Late Cretaceous)

Igneours Rocks can be indentified by Composition

- Felsic = high silica content (light color) - Mafic = low silica content (dark color)

divergent plate boundary

- Lithospheric plates move apart • form rift zones (continental-continental divergence)- example: East Africa • form oceanic ridges (oceanic-oceanic divergence) - Mid-Atlantic Ridge - Upwelling of asthenosphere at plate boundary injects molten mantle material to the surface, forming new oceanic crust• When new crust forms, it forces plates apart

Cinder Cones

- Minor explosive volcano - Mostly pyroclastic discharges of varying sizes - Pyroclastics build up around the vent creating cones- Example: Paricutin, Mexico; Cerro Negro, Nicaragua

Transformation Boundaries

- Plates "slide" past each other, side by side - Can offset oceanic ridges, breaking ridges up into short segments- separate continental plates • Example: San Andreas Fault, California and Mexico

Compression P Waves

-push-pull motion -travel through both solids and liquids -faster velocity

Identifying Minerals

-Analyze the mineral compositon -Measure crystal structure and symmetry -Observe physical properties

Why is the outer core liquid?

-Chemistry changes from a solid peridotite-based composition in mantle to an Fe and Ni based composition -Temperature is too high for Fe+Ni to be solid

Color

-Color of a mineral as viewed by the naked eye -Addiotnal information ussually needed

4) Volcanic Domes

-Composed of rhyolite, but can cause andesite lavas as well • Too viscous to flow - material oozes out to surface from a tube close to the vent • may explode as nuee ardente: a cloud of gas and ash---------Commonly occur at subduction zones after stratovolcano eruptions, hot spots under continents, and continental rifts--Vary in size

Earth's magnetic field

-protects us from harmful solar radiation -Without convection there is no magnetic field and radiation from sun would strip away the atosphere

Fissures

-Long, nearly vertical cracks where basalt lava emerges at large volumes -Fissures are where new crust is created at divergent plate boundary

seismic tomography

-Mapping S-waves (seismic tomography) indicates variations in temperature within the mantle, which are associated with mantle convection

Olivine

-No Cleavage -No oxygen atomsshared between tetrahedra -Major mantle mineral in peridotite

Element

-Number if protons dictates the chemical element -Elements are building blocks

Continental Drift Hypothesis Objections

-One of the major objections to the continental drift hypothesis was its inability to provide an acceptable mechanism for the movement of continents. -Wegner thought that the tidal influence of the moon could move the continents

P-Waves also have shadow zones

-P-waves refract at the outer core

Geodynamo

-Rapid motion of the liquid outer core stirs up electrical flow in the solid (iron) inner core, causing Earth's magnetic field. -Driven by outer core convection

Atoms

-Smallest Unit of matter an element can dividedwhile still retainging the chemical characteristics of that element -Composed of a nucleus surrounded by electrons

Impact of Earths Magnetic Field

-When magnetic minerals drop below their Curie temperature during solidification, they are aligned in the direction of an applied magnetic field (e.g. the Earth's magnetic field) -When magnetic iron emerges from the mantle at divergetingplates, it aligns with Earth's magnetic field before solidifying into rockAs the plates spread, rocks move away in both directions. A symmetric pattern occurs on both sides of the boundary, showing magnetic orientation through time

Hadeon Eon (4.6-3.8 billion years ago)

-accretion of the Earth from celestial debris -frequent celestial collision events -formation of the moon -water vapor condenses into liquid, forming ancient seas -formation of early atmosphere by de-gassing

Oceanic Crust

-has low silicia -has high density -Oceanic is thinner

Volcano

-location where materials from Earth's interior are extruded tothe surface of the Earth • Pyroclasts• Gases- Water vapor, CO2, SO2, H2S, HF• Sound - 1883 eruption of Krakatoa (Indonesia) heard 3,000 miles away• "loudest sound in history" LithosphereSide ventPipe Central ventLava flowsMagmachamberMagma, which originates in the asthenosphere ...... rises through the lithosphere to forma crustal magma chamber.As pressure builds, lavas and/or pyroclasts erupt through a central vent and side vents, ...... accumulating onthe surface to buildthe volcano.Standard model of a volcano Types of lavas1. Basaltic lavas• Highest temperature (1000−1200ºC)• Lowest viscosity• Form basalt igneous rock (mafic)2. Andesitic lavas• Intermediate viscosity, temperature

clastic sediments

-particles produced on Earth's surface resulting from the breakdown of rocks at the surface. -Sediments can be individual minerals or smaller pieces of rock

Seafloor Spreading

-seperation of liospheric plates at mid ocean ridges -Plates must be destroyed at the edge by subduction at convergent plate boundaries to balance out the creation of new oceanic crust

Shear S waves

-side to side motion -travel only through solids slower velocity

Cleavage

-the tendency of a mineral to break along flat surfaces -Bonding forces between atoms not equal in all directions whic creates planes of weakness along which the mineral tends to break -minerla strongly bonded in all directions such as quartz and garnet have no cleavage -weak bonds= good cleavage

Two main types of Igneous Rocks

1) Plutonic/Intrusive rocks - magma cools within the crust and does not make it to surface; cooling is slow 2) Volcanic/Extrusive rocks - magma reaches the Earth's surface as lava flows or explodes as pyroclastic fragments; cooling is fast

Density is dependent on

1. Chemistry 2. Pressure and temperature

Divergent Valley process

1. Continental Rift Valley 2. Water fills in rift valley and forms narrow seas/lakes 3. Larger seas begin to form and new oceanic crust begins to form 4. what started as continental divergence is now oceanic divergence Ex: Arabian plate and African plate

P waves indicate two types of crust

1. Oceanic crust = low silica (Si) = high density = faster P-waves (~7 km/s) 2. Continental crust = high silica = low density = slower P-waves (~6 km/s)

Most fatalities from volcanic eruptions associated with:

1. Pyroclastic flows = avalanche of ash and volcanic debris2. Indirect effects (mostly famine)3. Tsunamis

Steps for turning clastic sediments into sedimentary rock:

1. Weathering 2. Erosion 3. Deposition / Sedimentation 4. Burial and compactionORCementation 5. Diagenesis / Lithification

Types of volcanoes

1. shield volcanoes 2. stratovolcanoes 3. cinder cones 4. volcanic domes 5. fissures

Pyroxenes

2 perpendicualr cleavage planes at 90 angles 2 oxygen atomes

Earth's center is about _____ deep

6400 km/ 4000 miles

Volcanic Bomb

= large, solidified lava extruded from volcano

Hardness

A measure of how easily a mineral can be scratched High Hardness=less easily scratched -Depends on: -Size -Charge -Packing -Mohs Hardness Scale: higher number can scratch lower

Anion

A negatively charged ion

Cation

A positively charged ion

Ion

An atom or group of atoms that has a positive or negative charge.

Pluton

Any magma that has intruded and solidified into rock at depth

Convergent Plate Boundaries

Areas where plates move toward each other and collide, causing uplift. Three Types: - Lithospheric plates move toward each other • Continental-oceanic - examples: Oregon/Washington; Andes Mountains (west coast South America) • Oceanic-oceanic - examples: Japan; southern coast of Alaska • Continental-continental- example: Himalaya Mountains (between India/China)

Sandstones (in particular) are also classified by mineral composition Four major compositional groups:

Arkose = feldspar-rich Quartz arenite = quartz-rich Lithic = particles of other rocks, rather than minerals Graywacke = a sandstone cemented with clay mineral matrix (kaolinite)

Volcanism and the Atmosphere

Ash and gas entering atmosphere can cause climate changes Short term example:Mt Pinatubo eruption in 1991 Long term example:Siberian traps 251-250 mya

Theory of Plate Tectonics

By the 1960s, the continental drift hypothesis evolved into the theory of Plate Tectonics ➢The crust is broken up into rigid lithospheric plates ➢Plates are moving, not the continents themselves ➢Driven by mantle convection causing seafloor spreading

Main siliciclastic rocks based on texture:

Clay becomes shale or claystone Clay + silt becomes mudstone Silt becomes siltstone Sand becomes sandstone Gravel becomes conglomerate or breccia

Nucleus

Control center of the cell, composed of protons and neutrons

What drives plate tectonics?

Convection in mantle upwells heat and magma from mantle to surface at divergent plate boundaries- New oceanic crust formed as old crust pushed away from spreading centers

Bioturbation Structures/ Trace fossils

Evidence that living organisms were present without any remains of the organism

Mineral Composition: Four total compositional groups, based on chemistry of the source magma (mainly silica content):

Felsic igneous rocks (high silica) Intermediate igneous rocks (medium silica) Mafic igneous rocks (low silica) Ultramafic igneous rocks (very low silica)

Igneous Rocks

Form directly from cooling of magma or lava. Ex: granite (magma) and obsidian (lava)

Chemical sedimentary rocks

Formed by chemical processes NOT involving living things

Clastic sedimentary rocks

Formed from clastic sediments

Gases extruded from volcanoes cause ___________ from where trapped gases have escaped; common in basalt and pumice

Gases extruded from volcanoes cause vesicles (bubble holes) from where trapped gases have escaped; common in basalt and pumice

Graded Bedding

Gradual change of one sediment size into another; coarser/heavier sediments are deposited firstExample from underwater landslides (turbidity currents)

Volcanism and the hydrosphere

Groundwater that comes in contact with magma is heated, forming: fumarole - vents emitting steam geysers - vents emitting hot water

Shield volcanoes

Large, flat, shield-like shape • larger area relative to height - Form basalt lava; thin basalt flows build up over time- Most common at hot spots - Relatively predictable and "quiet" eruptions- Examples: Hawaiian Islands (Kilauea; Mauna Loa)

At intraplate hot spots, mantle material directly affects interior of the plate

Mafic igneous rocks form when hot spot is under oceanic crust

Cross-bedding

bedding on an angle to the main bedding plane

Example of Ionic Bond

Na+ and Cl- = NaCl

Benefits of volcanoes

Natural resources for humans • Main sources of metal and sulfur ores • Geothermal energy Provide nutrients to ecosystems living around volcano

Electrons

Negatively charged particles that orbit the nucleus

Earth's Magnetic Field

Orientation of magnetic "compass needle" will vary depending on latitude

Feldspars

Orthoclase feldspar AKA potassium felspar AKA microcline • KAlSi3O8 • Pink-ish/orange-ish • Plagioclase feldspar• (Ca,Na)AlSi3O8 • white • All 4 oxygens shared• 2 cleavage planes at 90°

Three types of Seismic Waves

P waves, S waves, surface waves

Inner Core

P-waves abruptly increase in velocity at around 5150 km depth where core becomes solid Solid because pressures are soimmense that Fe and Ni composition solidifies, and density increases

Two things can happen when waves encounter a change of density :

Reflection = wave will "bounce" off the boundary Refraction = wave will continue through the boundary, but at a different velocity

As pressure increases with depth, less and less peridotite can be melted, so

S-wave velocity increases again

Quartz

Sio2 -All 4 oxygens shared -No Cleavage -Color varies

Igneous Rocks can be identified by texture

Texture = size of mineral crystals - Phaneritic = coarse/large (slow cooling) - Aphanitic = fine/small (fast cooling) - Porphyritic = mix of large and small (fast for some minerals, slow for others) - Glassy = no crystals (super fast cooling)» 2 types: "Frothy" and "Compact"

Example of Magnmatic Intrusion

The Palisades Intrusion

continental drift

The hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present locations 1. "Jigsaw-puzzle" fit-shapes of continent appear to fit together 2. Rock sequences-similarity of rock assemblages and ages across oceans 3. Fossil assemblages 4. Glacial evidence

Subduction

The process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary.

Country Rock

The rock into which the magma has intruded is

Luster

The way a mineral reflects light Two major categories: Metallic and Non Metallic

Planetary Differentiation

This is a process in which more dense materials of a planet sink to the center, while less dense materials stay on the surface.

San Andreas Fault

Transform boundary between Pacific Plate and North American Plate (California, Mexico); continental-continental

The outer core must be liquid

True

A P-wave that crosses the Moho will be recorded on a seismograph before a P-wave that remains in the crust

True!-P-waves refract at the Moho, so velocity will increasebecause of the lower Si content (higher density) in the mantle, reaching a seismograph before a slower P-wave remaining in the lower density crust

Cementation

new minerals are precipitated into the void space between sediments

Convergent Plate Boundaries- Volcanoes

Volcanoes at convergent boundaries tend to be composite volcanoes (stratovolcanoes) • If oceanic-continental convergence, lavas are most often andesitic - Fluid-induced melting - rhyolitic can occur under specific conditions • If oceanic-oceanic convergence, lavas are most often basaltic- No continental crust in fluid-induced melting

What is a mineral?

a naturally occurring, inorganic solid that has a crystal structure and a definite chemical composition Ex Gold Not ex: wood, water, steel

Magnetic Chron

a period of normal (black) or reverse (white) polarity

calcile diagnostic property is

a reaction with acid

Peridotite

a rock with low Si, high Fe and Mg

Hot spots

are areas of upwelling magma located in the interior of a plate, not at a plate boundary -Position of volcanic island groups (like Hawaii) trace the direction and speed of the plates over fixed hot spots in the mantle

Sedimentary Basins

are depressions filled with thick accumulations of sediment.

Atomic Mass

atomic number + number of neutrons

Sillica tetrahedra

basic structure of sillicate materials

When oceanic plate meets oceanic

both plates are mafic; so magma is usually mafic

Moho discontinuity

boundary between low-density rocks of the crust with higher density rocks of the mantle

2) Stratovolcanoes / composite volcanoes

built up of layers of lava and pyroclasts - Andesitic lavas plus pyroclastic layers form a tall volcano- Usually associated with subduction zones - Tend to be violent and explosive eruptions - Examples: Mount St. Helens (WA); Cascade Range (WA/OR); Mt Shasta (CA); Fujiyama, Japan

When oceanic plate meets continental, magma begins with mafic composition

but becomes more intermediate/felsic when overlying continental crust is melted

Mudcracks

clayey desiccation features indicating water was evaporated from a lake bed

Mineral Physical Properties

color, hardness, cleavage, luster, density, crystalline form

Limestone

composed of biologically precipitated carbonate mineral calcite CaCO3. There are various types, including: Fossiliferous limestone -- visible fossils Reef limestone -- visible coral reef fossils Coquina -- broken fragments of shell pieces Oolitic limestone -- pearl-like grains (ooids) Chalk -- fine-grained calcite

Two Types of Crust

continental and oceanic

Surface Waves

don't enter Earth's interior

Paleomagnetic Time Scale

established by measuring the magnetic polarity of lava flows of known age

Bowen's reaction series

explains the sequence of fractional crystallization

Sedimentary structures

features in sediments and sedimentary rocks formed at the time of deposition

Depostion

forces of erosion/transport cease and the sediment comes to a rest.

Pillow basalt lavas

form on sea levels

Bedding

formation of parallel layers of sediment as particles are deposited

Ironstones

formed when dissolved iron in low-oxygen environments is later exposed to oxygen and precipitates

Lithosphere

hard, brittle (rigid) solid made of crust and uppermost portion of mantle

Convection

hotter, less dense material rises, while cooler, denser material sinks, then the pattern

P waves velocity _____ with density

increase

Dike

intrusion crosses (not parallel to) the country rock layers ("against the grain") • Neck = dike exposed at land surface

Sill

intrusion parallel to the layering of country rock ("with the grain")

The eruption of Mt Pinatubo ejected so much ash into the atmosphere (blocking the sun's rays) that

it dropped Earth's temperature for over a year

• Large Igneous Provinces

large areas of mafic igneous rocks believed to be caused by hot spots

Batholith

large dome-shaped mound• >100 square km • Frequently form the "cores" of mountains

pahoehoe lava

less viscous "ropey"

Shadow Zones

locations on Earth's surface where no body waves from a particular earthquake can be detected

Siltstone

made from silt; if particles are visible, they are very small and not easy to see

Conglomerate and Breccia

made of gravel sized particles cemented with sand, silt, and/or clay Deposited in very high energy environments: large floods, avalanches

Seismographs

measures and records earthquake magnitude based on the energy released in an earthquake. -P waves arrive first -S waves arrive second -surface waves arrive last

Chert

micro fossils from silica-fixing lifeforms, rather than calcite

Evaporites

minerals left behind salt water evaporates

Mudstone

mix of clay and silt particles

Mineral composition of particles

more = less mineral variety

Rounding of particles

more distance = more rounded

Transport of Sediments: Size of particles

more distance = smaller

Sorting of particles

more distance = well sorted

aa lava

more viscous, sharp jagged

S-Waves indicate

multiple zones within the mantle based on effects of temperature and pressure on peridotite -These velocity changes are not caused by changes in chemical composition

At continental-continental divergent plate boundaries

new oceanic crust is created, but melts overlying continental crust and creates intermediate and felsic compositions

Ophiolite suite

pattern of rocks formed by decompression melting that has since been brought onto land

The boundary between the lithosphere and asthenosphere coincides with melting temperature of

peridotite

Peat

plant remains indentifiable as plant remains

Magmatic differentiation

processes by which rocks of varying mineral composition can arise from a uniform parent magma.

Compaction

removal of air and water in void space between particles -Compaction by

Calcite

reacts with acid

Radical

refers to a compound with a negative charge

Well sorted sediment

refers to sediments with similar size, shape, and mineral composition

Wave speed and arrival times will depend on the

resistance to compression (P) and shear (S) of the material the waves must travel through before reaching the seismograph

Chemical Weathering

rocks are broken apart after changing chemical composition• oxidation, dissolution

Physical Weathering

rocks stripped apart by abrasive stresses• flowing water, wind, frost

Sandstone

sand sized particles; particles are visible

Burial and compaction

sediments are buried under additional sediments over time; enough pressure builds and they become more tightly packed

So how do we know about the interior of the earth?

seismic wave

Laccolith

small dome-shaped mound

Volcanic Ash

smallest pyroclastic fragments; form tuffs and weld together breccias

volcanic ash

smallest pyroclastic fragments; form tuffs and weld together breccias

Asthenosphere

soft, ductile (plastic) solid below the lithosphere

Pyroclasts

solid fragments extruded from volcanic eruption; cause pyroclastic texture Pyroclasts include ash, pumice, fine solidified magma combined into a rock

super continent cycle

splitting of Pangea into two continents; supercontinents form and break over millions of years

Metallic

strong light reflection; looks like a metal

Geoid

the actual shape of the earth

Massive Form

the appearnace of a large mass no obvios appearance of crystal form at macroscale

Moho

the boundary between the earth's mantle and crust

Weathering

the breaking down of rocks into sediments

Streak

the color of a mineral's powder Every mineral will have a diagnostic streak color Minerals of the same color can hvae different streaks

Crystal Form

the growth shape pf a mineral; based on arrangment of atoms Ex: Cubic, Dodecahedral, Octohedral, Prismatic

Atomic Number

the number of protons in the nucleus of an atom

Fractional crystallization

the process by which the crystals are formed in a cooling magma and are segregated from the remaining liquid. Temperature dependent; the first minerals to crystallize from a cooling magma are the ones that are the last to melt.

Viscosity

the resistance of a fluid to flow • High viscosity = more resistant to flow- Flows more slowly, thicker- Example: ketchup • Low viscosity = less resistant to flow - flows more easily, faster- Example: water

Diagenesis / lithification

the sediments become a sedimentary rock

When extrapolating to the core-mantle boundary

the spatial and temporal variations of the magnetic field are more apparent

Bedding plane

the surface separating one bedding layer from another

When P waves abruptly increase to 8 km/s

this signifies the Moho -Indicates thickness of continenetla vs ocean crust -Indicates compostion (low si) of mantle

Igneous Rocks are linked

to plate tectonics

gravity variations affect the geoid

true

Pole migration is caused by

variations of fluid movement in the outer core that affect convection strength

Sillicate group

variety of compounds based on silicon and oxygen -Mafic silicates are erromagnesian (higher in fe and Mg, lower in Si) -Felsic silicates are Non-Ferromagnesian

Bedding sequences

vertically stacked bedding with different types of sedimentary rocks and/or structures in each layer.

Ripples

wave-shaped features showing direction of movement

Seismic Wave

waves of energy produced by an Earthquake

Erosion/Transport

weathered material (sediment) is moved away from source rock and transported to another location• By streams, coastal waves, wind, glaciers

At intraplate hot spots, mantle material directly affects interior of the plateFelsic and intermediate igneous rocks form

when hot spot is under continental crust

Covalent Bond

with electrons shared -atoms share valence (outermost) electrons -By sharing each atom then has stable number electrons Stronger the ionic bond

Yellowstone Supervolcano

• 3 large eruptions in the past 2.1 m.y. • average 730,000 years between eruptions • last eruption 640,000 years ago • Another eruption could have huge effects on agriculture worldwide for at least 1-2 decades • No indications that eruption will occur any time soon!

Sedimentary Rocks

• 5% of rocks in crust • 65% of rocks exposed at land surface • Contain - Evidence of past environments • Oceans, mountains, rivers - Evidence of past climates • Temperature, rainfall, oxygen - Evidence of past animal and plant life• All fossils are found in sedimentary rocks

1980neruptions of Mount Helens Washington

• 63 casualties from lahars (mudslide) that reached almost 50 miles away and destroyed forests in 230 sq mile area• Ash cloud spread over 11 states

Other Mineral Groups

• Carbonates - cation + CO3 - Example: calcite CaCO3 • Sulfates - cation + SO4- Example: gypsum CaSO4 • Sulfides - cation + sulfur (S)- Example: pyrite FeS2• Oxides - cation + oxygen- Example: hematite Fe2O3 • Native elements - mineral composed of single element- Carbon as diamond and graphite- Copper, gold, silver, platinum- Sulfur

Cenozoic Era (the current era)

• Effects of Pangea breakup continues to today - Formation of the Alps • between Italy and France - Formation of the Himalayas • between India and China - Widening of the Atlantic Ocean - Beginning of East African rifting • centered in Ethiopia

Divergent Plate Boundaries

• Fissures at seafloor spreading ridges - Most voluminous volcanic activity • ~ 30,000 miles of ridges on earth - Mostly under oceans - except Iceland - magma typically melted asthenosphere material rich in ultramafic rock (peridotite) - basalt emplaced as new seafloor at spreading ridge or rift • Fissures at continental rifts - Magma melts overlying continental crust, may produce andesite or rhyolite lavas in addition to basaltic - Examples:• East African Rift

Biological sedimentary rocks

• Formed by chemical processes involving living things

Predicting Volcano Eruptions

• Fortunately, in modern times we have a better sense of when a volcano is set to erupt • Precursors that begin to increase leading up to an eruption are clues to increased likelihood of eruption - Seismic activity (earthquakes) - Ground deformation (slope angles, landslides) - Gas emissions - Thermal emissions

Present and Future Volcanic Hazards in the United States

• Hawaii • South-central Alaska & Aleutian Island chain • Cascade Range - Washington, Oregon, northern CA, southwestern Canada • Yellowstone Supervolcano - Wyoming, Montana

Locations where sediments are deposited: Continental

• Higher-energy transport • Coarser grain sizes deposited

Rhyolitic Lavas

• Highest silica content, viscosity • Common where magma melts large quantities of continental crust

Basaltic lavas

• Highest temperature (1000−1200ºC) • Lowest viscosity • Form basalt igneous rock (mafic)

Andesitic Lavas

• Intermediate silica content, viscosity • Common at subduction zones

Andesitic lavas

• Intermediate viscosity, temperature • Form andesite igneous rock (intermediate)

Micas

• KAl2(AlSi3O10)(OH)2 • Muscovite (lighter) • K(Mg, Fe)3AlSi3O10(OH)2 • Biotite (darker) • 1 cleavage plane • 3 oxygens shared = stacked sheets of tetrahedra

Locations where sediments are deposited: Marine (sea/ocean)

• Lower-energy transport • Finer grain sizes deposited

Rhyolitic lavas

• Lowest temperature (600-800ºC) • Highest viscosity • Form rhyolite igneous rock (felsic)

Intraplate Volcanism

• Magmas associated with a mantle hot spot in an oceanic crust produce shield volcanoes of basaltlava - Example: Hawaii • Magmas associated with a mantle hot spot under continental crust will produce more felsic lavas; often as explosive eruptions- Example: Yellowstone Supervolcano

Lines of evidence that led to Plate Tectonic theory:

➢Sea floor mapping ➢Topography ➢Locations of earthquakes and volcanoes ➢Sea floor ages ➢Paleomagnetism / magnetic pole reversals