Marine Science 304 Lecture

Drilling a hole.
examine volcanic matter
study meteorites
geophysical data

sudden motion of the earth caused by the release of energy stored in rocks

surface above the focus

initial rupture point of an earthquake

compressional
speed, ~8 km/sec on the surface
move along travel
travel through solids and liquids

shear waves
speed, ~4 km/sec on the surface
move perpendicular to travel
CANNOT travel through liquids

~105-140 degress

density, pressure, temperature, viscosity, phase

sudden speed increase

sudden speed drop

continental (granite) and oceanic (basalt)

~35 km thick
denisty 2.7 g/cm^3
aluminum silicates, granite

~11 km thick
density 2.9 g/cm^3
magnesium silicates, basalt

Latitude Change
Free-Air Anomaly
Bouguer Anomaly

the earth is in gravitational equilibrium through a buoyancy mechanism

fossils
rock formations
ages
proximity of locations and motion

magnetism and sediment thickness
crustal age increases away from the ridge
with spreading, older crust moves away from ridge

formed at ridge with "current" polarity.
with spreading, moves away from ridge.
polarity switches.
produces mirrored bands of crust

"spreading center"
formation of new oceanic lithosphere

when move away from hot MOR, the temp decreases. Decreasing temp leads to compression of oceanic rock and increasing density. More and more sediment deposits on top and sediment's gravity pushes down the oceanic rocks. Gravity of plate slab pulls down on plate

sediment thickness increase away from the ridge. With spreading, more time for sediment accumulation

Passive margins
active margins
transform margins

trailing edge margin
divergent margin
aseismic margin

within a single plate
accumulate large thickness of sed.
few earthquakes
most of atlantic ocean margin
smooth topographic relief
stable but slowly, continually subsiding

salt deposits or mobilized mud
less dense than overlying sediments
salt rises upwards and forms diapirs

leading edge margin
convergent margin
seismic margin

an actively deforming region where 2 tectonic plates move toward one another and collide.
frequent earthquakes
most of pacific plate margin
along destructive plate boundary
3 types of convergeny boundaries

sites of subduction of one plate into the other
faster subduction could result in a deeper and narrower____

low angle thrust faults

type of break across which older strata are pushed up and over younger strata

translation margins
result from horizontal shear motion
shallow focus earthquakes
can be both active and passive
occur in both pacific and atlantic oceans

cycle takes about 500 Ma
6 stages

embryonic
juvenile
mature
declining
terminal
suturing

Motion: uplift
Features: rift valleys and lakes
Example: East African Rift Valleys

Motion: divergence
Features: narrow sea with matching coasts. Oceanic ridge formed
Example: Red Sea

Motion: divergence
Features: ocean basin with continental margins. Ocean continues to widen at oceanic ridge.
Example: Atlantic Ocean

Motion: convergence
Features: subduction begins. Island arcs and trenches form around basin edge.
Example: Pacific Ocean

Motion: convergence
Features: oceanic ridge subducted. Narrow, irregular seas with young mtns.
Example: Med. Sea

Motion: convergence and uplift
Features: mtns form as 2 continental crust masses collide, are compessed and override.
Example: Himalaya Mtns.

used to be 4 plates. (Pacific, Kula, Farallon, Phoenix)
3 of plates were destroyed. Australia separates from Antarctica; moves N closing Tethys Seaway. Pacific plate relative shift from N to NW motion. East Pacific Rise rotates clockwise and intersects with N. Am. Plate.

a rigid unit of lithosphere that moves as a unit

pacific, north american, south american, eurasian, indian, antarctic, australia

divergent, convergent, transform

moving apart
mid ocean ridges and rift valleys

moving together
tenches, mountains, volcanoes

moving together
trenches, island arcs, volcanoes, marginal seas

moving together
mountains

plates slide pass each other
usually offset segments of ocean ridges

1. sediment
2. basalt
3. Gabbro
4. Peridotite

Aphanitic.
Mafic.
cools fast

Phaneritic.
Mafic.
Cools slowly

Phaneritic.
Ultramafic.
Cools Slowly

large crystals, slow cooling, intrusive rock, magma

small crystals, fast cooling, extrusive rock, lava

French American Mid-Ocean Undersea Study.
Study of MOR

pressure and temperature
crystal fractionation
chemical content
volatile content
speed of rise

hot spots and MORs

asthenosphere rises and fills gap between spreading paltes. Magma enters chamber. Crystals form and settle out.

form basalts/gabbros in magma chambers.
erupted along fissures and cools as dykes
magma chamber cools as gabbros

Outer Core

Passive margin or a trailiing edge margin

shear waves

pressure increases, temperature increases, and density increases

deep

maringal basin

coral reefs, basin highs, salt diapirs

outer core