Please upload a filled out version of the Plate Tectonics table.
Upload signed / dated images of your GCM and Ocean Gyres. The GCM drawing should show a sketch (with arrows) and verbal labels for all 10 features requested on the form. Do NOT enumerate features (do not label them as numbers). You may use colors but color coding will not be counted as labels.
The gyres should be correctly located, show correct direction of motion with arrows and have ‘W’ and ‘C’ labels on east and west sides showing cold and warm currents.
Your work must be original.
|
Major Margin Type |
Ocean /continent subtypes |
Arrows and symbols |
Real world example |
Major features |
||||||||||||||||||||||||||||||||||||||||
|
Convergent |
ocean / continent |
|
||||||||||||||||||||||||||||||||||||||||||
|
na |
||||||||||||||||||||||||||||||||||||||||||||
|
Divergent |
||||||||||||||||||||||||||||||||||||||||||||
|
Continent – failed rift |
||||||||||||||||||||||||||||||||||||||||||||
|
Transform |
||||||||||||||||||||||||||||||||||||||||||||
|
Other features |
||||||||||||||||||||||||||||||||||||||||||||
|
Passive margin |
||||||||||||||||||||||||||||||||||||||||||||
|
Hot spot |
Ocean | |||||||||||||||||||||||||||||||||||||||||||
|
Continental |
Drawin and label the following GCM features. Double check your arrows and make sure they are pointing the right direction.
Directions matter in Earth Science.
1. Polar highs
2. Westerlies
3. Trade winds
4. Equatorial low
5. Hadley Cell (with arrows)
6. Subtropical highs
7. Intertropical Convergence Zone (ITCZ)
8. Subpolar Lows
9. Polar Easterlies
10. Jet stream
Draw in the five ocean gyres. Make sure the arrows make sense. Label the warm and cold currents as ‘W’ and ‘C’ respectively on the appropriate sides (east and west) of the gyres. Do not label north / south as cold / warm. We know the poles are cold and the equator is warm.
This second diagram is just for practice if you need it:
Plate
Tectonics
Seismic tomography
teleseismic imaging – using earthquake
waves to image the Earth’s interior
Seismic Tomography
Difference in arrival time at point along a surface showing various wave
types. In reality there are many different wave sets some of which pass
through the core. These all lead to very accurate location of the quake.
Tomography : An MRI of the Earth
Seismic waves are sent deep into the Earth and geophysicists study the
patterns when they come back to the sensors. A network of seismographs also
has monitored world-wide earth quakes since 1960. The earthquakes provide
a kind of mega-sonar that has provided geophysicists with compelling images
of plates as they dive into the mantle at subduction zones
.
What the mantle really looks like….
(Composite images outline cold,
downgoing ocean plates as areas where
seismic waves speed up).
– Physical properties framework: how does
it behave mechanically (Lithosphere /
Asthenosphere / Mesosphere / Outer Core /
Inner Core
Compositional framework – what is it made
of. Crust / Mantle / Inner Core / Outer Core
Earth’s compositional layers.
Crust = enriched in Si
Mantle = enriched in Fe, Mg
Subduction zones form crust through
dehydration
melting (water entrained by the
down-going plate). Spreading ridges form crust by decompression melting.
Both types of crust are created by convection. Mantle plumes push the ocean floor
apart at spreading ridges. Subduction zones form magma that rises to form
volcanoes
.
Crust consists of ‘continental’ and ‘oceanic’ crust.
Melting Processes:
The Earth’s interior gets hotter as you go down (this is known as the
geothermal gradient).
Decompression melting – melting due to a lowering of lithostatic pressure.
This creates ocean crust from mantle material leading to Fe, Mg enrichment
Dehydration melting – melting due to the addition of water. This creates
continental crust from partial melting leading to Si enrichment.
decompression
dehydration
Development of the Crust
The crust is created at spreading ridges through decompression melting of
the mantle (which is enriched in Fe and Mg) and at subduction zones
through dehydration melting (which causes enrichment in Si, Na, Al, K)
The long term effects of exchange has made continental crust enriched in Si,
Na, Al, K relative to ocean crust, which is relatively enriched in Fe and Mg.
mantle peridotite (high Fe, Mg; dense,
heavy; primordial starting material)
Olivine – (Mg,Fe)2SiO4
Pyroxene – (Mg,Fe,Ca)xSi2O6
subduction
sea floor
spreading
Ocean vs. Continental Crust
Oceanic crust thinner (5 km), younger
(< 200 Ma) and denser (more Fe,Mg).
This is because it comes directly from
the mantle which has more Fe and Mg
than the silica-rich crust.
Continental crust is thicker (15 km),
older (< 3.8 Ga) and less dense (more
Si, Al). This is because subduction
magmas preferentially melt silica.
Ocean crust is typically darker
because of its higher proportions of
Fe and Mg. It is referred to as ‘mafic’
after magnesium (ma) and iron (Fe).
Continental crust has higher Si, Al,
K) and is referred to as ‘felsic’ (after
the mineral felspar.)
In the Beginning
The issue of the age of Earth and evidence of significant forces
acting on the crust contributed to the thinking that the surface of the
Earth had unknown forces acting upon it.
“In the mountains of Parma
and Piacenza multitudes of
rotten shells and corals are to
be seen, still attached to the
rocks…” Leonardo Da Vinci
Clues
Early cartographers noticed how continents naturally fit together.
Fossils and rock types were similar among distant continents.
1596 – Ortelius
hypothesizes
continental drift in his
atlas, Thesaurus
Geographicus,
Benjamin Franklin
was also a supporter.
Basalt – Nova Scotia Basalt – Morocco
Certain types of
rocks can only be
formed by
glaciers.
Glossopteris
Pangea, The Supercontinent
Volcano in Italy Coal beds in Germany
Wavy layers in Switzerland Layers at different angles in England
Different ideas depended on what naturalists could see around them.
Earthquakes and Volcanoes
Geologists and
geographers saw
that earthquakes
and volcanoes are
clustered
together. They are
also tend to be
associated with
prominent
geographic
features like
mountain ranges
or submarine
trenches.
Magnetic Anomalies
.
Basalt erupts from submarine volcanoes and records the orientation of the
Earth’s magnetic field at the time of submarine eruption.
Olivine – (Mg,Fe)2SiO4
Pyroxene – (Mg,Fe,Ca)xSi2O6
Wegener’s Hypothesis
PhD: Astronomy
Title: Meteorologist
Hobby: Record holding balloonist
Controversial Theories: Continental drift
(1915), the existence of the Jet Stream
Death: got lost in a blizzard in Greenland
the day after his 50th birthday.
Wegener knew that the continents had
moved around based on his studies of
plate reconstructions, but there was little
evidence of whole continents actually
moving. Wegener hypothesized the
correct mechanism for how plates moved
(convection) but scientists did not have the
technology to ‘see’ evidence of this yet.
Clearer images of the Earth’s surface
would later show what was going on.
Shape of the Sea Floor
Bear Seamount
MidAtlantic Ridge
Shallow volcanoes with coral
reefs that gradually subside.
H. Hess mapped
the seafloor with
sonar during
WWII.
Volcanic
chains
Linear valleys
Hess’ Transport Route
Philippines
Mariana Trench is the deepest part of
the ocean (6.77 mi) and is part of a
tectonically active region of the pacific
‘ring of fire’.
channels
volcanoes
The locations of earthquakes showed us that certain areas of the crust are
dynamic interfaces. The Earth’s crust consists of large regional plates that are
moving around on the surface.
The Earth’s plates are moved by Earth’s internal heat. As a mechanisms for
dissipating heat and material, plate tectonics changes the Earth’s surface,
making it a dynamic environment. Plate tectonics also creates a wide
diversity of environments on Earth’s surface.
Plate tectonics is
driven by mantle
convection. Convection
is density driven
movement of a fluid or
gas across a thermal
gradient. The less
dense (heated) mantle
plumes rise and exert a
lateral force on the
plates. This moves the
plates around. It also
helps generate new
crust in certain areas.
No other planet that
we know of has plate
tectonics.
Three Types of Plate Boundaries
Divergent Margins – plates moving apart, new crust created
Convergent Margins – plates moving together, crust is consumed
Transform Margins – plates slipping past each other
Divergent Margins
Plates can move away from each other due to divergent forces of
mantle convection cells and/or the pull of other plate interactions.
Divergent margins occur as mid-ocean ridges or continental rifts.
The fissures that form at divergent margins
are called ‘rifts’. New crust is created at
rifts in the form of magmas that erupt out of
volcanoes, vents and other volcanic
features.
mid-ocean ridge
continental rift
Rifts may start on land and then become ocean spreading ridges.
East Africa
Afar Triple Junction and the Great Rift
Valley:
Lakes, rivers, unique volcanism and
Earth’s next ocean
The nature of the rift geography and arid climate
lead to unique erosion and sedimentation patterns
in the Great Rift Valley. Due to these factors some
of the oldest and best preserved hominid fossils
were found here by Richard Leakey and others.
Iceland
Sea of
Cortez is
an active
rift zone
with a
strong
component
of strike
slip
motion.
Active Rifts: Baja
Failed Rifts = Rivers
The Mississippi
River flows
along the
Reelfoot rift, a
‘failed’ rift,
meaning it
opened a little
and then
became
dormant. Many
of the world’s
major rivers flow
along failed or
dormant rifts
(e.g.,
Rio
Grande
,
Amazon, Nile).
Mid-continent rift – ore,
deposits, lake basins
Reelfoot rift – Mississippi River,
New Madrid Fault zone.
Rio
Grande
Passive
Margins
Convergent
The down-going plate
goes under the over-
riding plate.
3. continent –
continent collision:
Mountains
2. ocean-continent
collision: volcanoes
and earthquakes
1. ocean-ocean collision:
volcanoes and
earthquakes
Himalayas
Continent – continent collision creates large mountains.
The Himalayas are so big relative to the Earth’s crust, they
are collapsing under their own weight. The extreme
elevation also leads to extreme erosion.
South America
Seismic tomography: what subduction
really looks like, plate has 3D structure
Longest continuous exposed mountain range on
Earth. Atacama Desert – highest, driest, desert
on Earth
Japan (also Indonesia and the
Philippines are island arcs where an
ocean plate is subducting beneath
another ocean plate.
South Sandwich Islands – underwater
volcanic arc near Antarctica. Arcs are chains
of volcanoes formed by subduction zones.
Mariana Trench: ocean – ocean subduction.
Trenches are the surface expression of where
ocean plates descend at subduction zones
New Zealand – Mixed Motion
Alpine fault is bound on both ends by subduction zones between the
Pacific and Australian plates. 300 miles of lateral offset, 43 miles of
shortening (or compression).
California
Carrizo Plain
The transform margin is actually a fault zone.
15 – 20 m.y.o,
350 miles of
lateral offset.
Hot Spot: the plate moves, and the mantle plume stays put.
Yellowstone is an example of a hot spot on land.
The Yellowstone caldera has produced the largest
known volcanic eruption on Earth.
Tectonic Cycle
Rifts form oceans with
passive margins on both
sides. The passive
margins accumulate thick
loads of sediment. The
heavy sediment pushes
down and initiates
subduction anew.
Supercontinents Past and Future
Continents are constantly moving.
Over Earth’s 4.5 billion year history,
they come together into super
continents and then move apart.
