Download Tectoinic Plates and Rock Cycle

Plate Tectonics
Continental Drift
Wegener proposed
_________
the theory that the
crustal plates are
moving over the
mantle.
Supported by:
Fossil, rock type
evidence and coastline
shapes.
Earth ~200 million years ago
The Geologic
Time Scale
Based on
*Fossils
*Correlation
Later
*Calibrated with
radiometric
dating
The Continental Drift Hypothesis
Proposed by Alfred Wegener in 1915.
Supercontinent Pangaea started to break up about 200
million years ago.
Continents "drifted" to their present positions.
Continental Drift: Evidence
Geographic fit of South America and Africa
Fossils match across oceans
Rock types and structures match across
oceans
Continental
Drift:
Evidence
Tight fit of
the continents,
especially
using
continental
shelves.
Continental Drift:
Evidence
Fossil critters and plants
Continental
Drift:
Evidence
Correlation of
mountains
with nearly
identical
rocks and
structures
Continental
Drift:
Evidence
Glacial features
of the same age
restore to a
tight polar
distribution.
The Rise of Plate Tectonics
U.S. Navy mapped seafloor with echo sounding
(sonar) to find and hide submarines. Generalized
maps showed:
oceanic ridges—submerged mountain ranges
fracture zones—cracks perpendicular to ridges
trenches—narrow, deep gashes
abyssal plains—vast flat areas
seamounts—drowned undersea islands
The Theory of Plate Tectonics
Earth’s outer shell is broken into thin, curved plates
that move laterally atop a weaker underlying layer.
Most earthquakes and volcanic eruptions happen at
plate boundaries.
Three types of relative motions between plates:
Why do the plates move?
Two related ideas are widely accepted:
Slab pull: Denser, colder plate sinks at subduction
zone, pulls rest of plate behind it.
Mantle convection: Hotter mantle material rises
beneath divergent boundaries, forces the cooler
material to sink at subduction zones.
So: moving plates, EQs, & volcanic eruptions are due
to Earth’s loss of internal heat.
Convection Currents
The force responsible for plate movement is __________.
How does convection
work? No one knows—
but they aren’t afraid
to propose models!
Whole-mantle convection
Two mantle convection cells
Complex convection
Divergent boundaries: Chiefly at oceanic ridges
(aka spreading centers)
Plate Boundaries
The following two slides show maps of the
current major plate boundaries and their
relative motions.
 You should be able to describe various
landforms created by different plate
movements.

Diagram of Lithospheric Plates and Their Interactions
Plate Boundaries
apart
Boundary – moving _____
together
 Convergent Boundary – moving ________
 Transform Fault Boundary – moving
sideways past each other
________________________
 Divergent
Divergent boundary of two continental plates.
rift
valley
East African Rift
Creates a __________. Example: _____________
Divergent
boundarie
s also can
rip apart
(“rift”)
continents
How rifting of a
continent could
lead to
formation of
oceanic
lithosphere.
e.g., Red Sea
e.g., East Africa Rift
e.g., Atlantic Ocean
Presumably,
Pangea was
ripped apart by
such continental
rifting & drifting.
Subduction zones form at convergent boundaries
if at least one side has oceanic (denser) material.
Modern examples: Andes, Cascades
Major features: trench, biggest
EQs, explosive volcanoes
Convergent boundary of two oceanic plates.
island arc and a _____.
trench Example: _____
Japan
Creates an ________
Another subduction zone—this one with
oceanic material on both sides.
Modern example: Japan
Earthquake depth indicates subduction zones
Convergent boundary of two continental plates. Forms
folded mountain range. Examples: ___________,
Himalayas
a ______
Appalachians
Alps, ______________
Collison zones form where both sides of a
convergent boundary consist of continental
(buoyant) material.
Modern example: Himalayas
This probably used to be a subduction zone,
but all the oceanic material was subducted.
Convergent boundary of an oceanic plate and a continental
volcanic mountain range and a ______.
trench
plate. Forms a _______
Cascades or _______
Andes
Examples: _______
Mts
Most transform
boundaries
are in the oceans.
Some, like the one
in California, cut
continents.
The PAC-NA plate
boundary is MUCH
more complex than
this diagram shows.
Transform-fault boundary where the North American
past each other.
and Pacific plates are moving ____
San Andreas Fault in California
Example: ________________
Hotspots, such as the one under Hawaii,
have validated plate tectonic theory.
Plate Boundaries Review





divergent
Places where plates move apart are called _____________
boundaries.
rift valley
When continental plates diverge a ___________
is
formed.
When two oceanic plates converge what is created?
an island arc and a trench
_________________
The Appalachians formed mainly from continental plate
folded
collisions and therefore are a __________
mountain
range.
Convection currents.
The force moving the plates is ____________
THE ROCK CYCLE
Relationships Between All Three
Rocks
All
three rocks are being
recycled and converted to all
of the classes
Rock Classification
Igneous

Description – forms the bulk of the earth’s crust.
It is the main source of many non-fuel mineral
resources.
–
 Intrusive Igneous Rocks – formed from
the solidification of magma below
ground
 Extrusive Igneous Rocks – formed from
the solidification of lava above ground
 Classification
Igneous (Continued)
– Granite,
Pumice, Basalt, Diamond,
Tourmaline, Garnet, Ruby,
Sapphire
Examples
Sedimentary
– rock formed from
sediments. Most form when
rocks are weathered and eroded
into small pieces, transported,
and deposited in a body of
surface water.
Description
– pieces that are cemented
together by quartz and calcium
carbonate (Calcite).
Examples: sandstone (sand stuck
together), Conglomerate (rounded
& concrete-looking) and Breccia
(like conglomerate but w/ angular
pieces)
Clastic
Sedimentary (Continued)
–
 Chemical Precipitates – limestone
precipitates out and oozes to the bottom
of the ocean (this is why there is a lot of
limestone in S.A.)
 Biochemical Sediments – like peat &
coal
 Petrified wood & opalized wood
 Nonclastic
Metamorphic
– when preexisting rock is
subjected to high temperatures (which
may cause it to partially melt), high
pressures, chemically active fluids, or a
combination of these
 Location – deep within the earth
 Description
Examples:
 Contact
Metamorphism- rock that is
next to a body of magma
Ex.
limestone under heat becomes marble
through crystallization

Limestone -> marble
sandstone -> quartzite
shale -> hornfelds (slate)

Dynamic Metamorphism – earth movement
crushes & breaks rocks along a fault. Rocks
may be brittle- (rock and mineral grains are
broken and crushed) or it may be ductile(plastic behavior occurs.)

Rocks formed along fault zones are called
mylonites.
Metamorphic (Continued)
Metamorphism – during
mountain building; great quantities of
rock are subject to intense stresses and
heat
• Ex. cont. shelves ram together
 Regional
Metamorphism –
One form of rock changing into
another
Progressive
shale->slate->schist->gneiss
coal->graphite
granite->gneiss
Oxygen

The most abundant element in Earth’s
crust.
Nitrogen

The most abundant element in the
Earth’s atmosphere.
Iron

The most abundant element in the
Earth’s core.