Solid Earth summary and notes

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Solid Earth summary and notes

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

quartz = 2nd most abundant

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

¼ 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))

Mountain Building

deformation of rocks and metamorphism of rocks are results of mountain building

response of rock to stress depends on temperature, pressure, strain rate and rock type

stress = pressure = force/area

compressional (usually in mtn building)

tensional (eg. Rift valley)

shear (eg. faults)

strike-slip faults vs dip-slip faults

normal fault, reverse fault, thrust fault

hanging wall and footwall

horst = uplifted block with faults on either side

graben = block that has dropped down

materials which break under stress = brittle

materials which deform permanently = ductile

folds = ductile deformation

folds which arch upwards = anticlines

folds that bend down = synclines

plane along middle of fold = axial plane

dip = angle layer makes with the horizontal

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.:

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)
rhyolite, high in silica, light-colored, thick and viscous, comes from molten continental crust, explosive, steep-sided volcanoes, stratovolcanoes (steep sides)
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

Geologic Time

relative dating – use geological record to order events sequentially
principle of superposition – oldest layers under newer layers
sediment settles in horizontal layers
principle of cross-cutting: fracture must be younger than the rock it cuts; feature that cuts across a rock must be younger than the rock it cuts
principle of inclusions – fragments of rock contained within another rock are older than the rock layer containing the inclusions

Source : http://www.csun.edu/~hmc60533/CSUN_300/300_S2005_solid_earth.doc

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