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PlateTectonics

By Linda Russell,2014-04-08 21:08
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PlateTectonics

    Earth Science 300

    Summary notes.

    Solid Earth

Minerals

     definition naturally occurring, inorganic solid, unique chemical structure

     made of elements, some just one, most more than one

     rocks = aggregate of minerals

     atomic structure protons, neutrons, electrons

     ion = atom which has gained or lost one or more electrons

     atoms bond to form compounds

     ionic bonding (some atoms lose electrons, others gain them; opposite charges attract)

     covalent bonding (atoms share electrons) - eg. in water to bond H and O atoms

     metallic bonding

     bonded chemical groups often found in minerals, e.g.

     carbonate, sulfate, hydroxyl, silicate

     mineral properties

     crystalline structure

     luster

     color

     streak

     fracture

     specific gravity (density)

     hardness (Mohs scale)

     cleavage

    4000 named minerals, 8 elements make up bulk of these minerals and represent over 98%

    of the continental crust:

     O (46.6%), Si (27.7%), Al (8.0 %), Fe (5%), Ca, Na, K, Mg

     Si + O make up silicates = most common mineral group (75% of earth’s crust)

     silica tetrahedron, chains

     2 groups of silicates:

     ferromagnesian (contain Fe and Mg) dark in color

     non-ferromagnesian

     feldspars are most plentiful over 50% of earth’s crust nd quartz = 2 most abundant

    silicates form from molten rock as it cools, and crystallize at different temperatures

    ? of the earth’s crust are nonsilicate minerals:

     carbonates = eg. calcite (major constituent of limestone and marble)

     gypsum

     halite (salt)

    gemstones (many have names different from their mineral names)

     diamond

     sapphire = corundum = aluminum oxide + impurities

     with titanium + iron (blue sapphire)

     with chromium (red ruby)

Rocks

     The Rock Cycle

     Igneous Rocks

     form as magma cools and crystallizes

     sometimes ejected in volcanic eruptions (extrusive or volcanic), contain vesicles

     sometimes crystallizes at depth in the earth (intrusive or plutonic)

    if magma cools slowly large crystals, quick cooling small crystals, instant quenching

     no crystals (glassy)

    Bowen’s series for crystallization temperature

    Classification of igneous rocks

     by amount of silica present

     rich = felsic (eg granite, rhyolite)

     intermediate (eg diorite, andesite)

     poor = mafic (eg. basalt, gabbro)

     low in silica = low viscosity = flows easily

     high in silica = high viscosity

     kinds of feldspars present, other minerals

     Sedimentary Rocks

     weathering moves particles and deposits them as a sediment

     compaction and cementation

     majority of rocks exposed at earth’s surface are sedimentary

     important for determining earth’s history (put down in layers, contain fossils)

     lithification (= transformation of sediments into sedimentary rock)

    2 sources of particles (solid from weathered rock = detritus) (soluble material =

    chemical sedimentary)

    detrital dominated by clay minerals and quartz

     classified by particles size (eg. conglomerate, sandstone, shale)

     particle size related to distance from source and transport mechanism

    chemical sedimentary rocks

     material carried in solution to lakes and seas

     physical precipitation

     biochemical (water ingested by water-dwelling creatures and solid material is

     precipitated out to make hard parts - eg sea shells)

     most abundant = limestone (calcite), 90% is biochemical

     halite (rock salt), gypsum, chert

     Metamorphic Rocks

     can form from igneous, sedimentary or other metamorphic rocks

     changed by heat, pressure, chemically-active fluids

     metamorphic changes take place a few km below earth’s surface

     metamorphism can align grains in rocks

     contact metamorphism rocks are heated by adjacent mass of hot rock

     limestone -> marble

     sandstone -> quartzite

     basalt -> amphibolite

Plate Tectonics

    evidence for movement of plates:

     continental fit

     glacial (including pattern of striations)

     fossil

     mountain ranges (Appalachians extend into Greenland)

    magnetic evidence (trace the apparent direction of the Earth’s N. magnetic pole)

     theory:

     discovery of Mid-Atlantic Ridge

     evidence of sea-floor spreading

    types of crust:

    continental, oceanic density difference oceanic is thinner and denser, continental is

    lighter and thicker. When 2 plates come together the oceanic plate is the one that

    subducts

     plate boundaries:

     divergent vs convergent know structure of these (eg. subduction cross-section)

    divergent:

    oceanic: Mid-ocean ridges with rift valley

    continental: eg. East African rift valley

    convergent:

     oceanic-oceanic: volcanic island arc, offshore oceanic trench, eg. Aleutian islands

     oceanic-continental: volcanic mountain belt, orogenic mtns, eg. Andes

     continental-continental: (collisional) mountain belt (only minor volcanism) eg.

    Himalayas

     transform:

     fault valley, eg. San Andreas fault

     right lateral vs. left lateral

     driving force = convection in the mantle, push-pull force in slab

    hotspots:

     fixed point sources of heat (rising magma)

     moving plate causes chain of islands to form

Earthquakes

     focus (= location of rupture within the earth)

     shallow, intermediate, deep

    epicenter = point on earth’s surface above focus

     determining the position of the epicenter

    location of earthquakes (on plate boundaries)

     seismic waves

     body waves (P and S waves)

    P waves = primary = compression waves = fastest

    S waves = secondary = perpendicular to direction of propagation, do not travel

    through liquids, slower (do not travel through outer core, produce shadow zone)

     surface waves (produce rolling or swaying motion)

     determining earthquake location from 3 seismographs

     intensity and geology (build your house on rock)

     magnitude (Richter scale)

     intensity (Mercalli scale)

Internal Structure of Earth

    inner core solid (iron with nickel)

    outer core liquid (iron + nickel)

    mantle = silicates

     lower mantle = rigid

    upper mantle = asthenosphere (plastic) + lithosphere (solid includes oceanic (basaltic)

    and continental crust(granitic))

Volcanoes

     molten rock below surface = magma

     molten rock on surface = lava

     types of igneous rock

    relationship between amount of silcate in rock, viscosity of rock, type of volcanic explosion,

    type of volcano, ie.:

    1. basalt, low in silica, dark in color, runny, flows easily, can flow through cracks

    (fissures), comes from mantle and molten oceanic crust, forms non-explosive

    volcanoes, shield volcanoes (broad domes)

    2. rhyolite, high in silica, light-colored, thick and viscous, comes from molten

    continental crust, explosive, steep-sided volcanoes, stratovolcanoes (steep sides)

    3. andesite, intermediate rock (named from Andes mtns) when melted oceanic crust

    or magma from deep in mantle mixes with molten continental crust, eg. under

    oceanic-continental convergent plate boundary

     3 places where volcanoes occur:

    Rifts (oceanic or continental )

    Hot spots

    Subduction zones

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