Download Notes class_5_6_7

Plate Tectonics: How it works
All material contained here are figures from Understanding Earth by
Grotzinger, Jordan, Press, and Siever.
Or they are original figures by Harold Gurrola
Convection:
•A means for moving heat from deep in the Earth to the surface by
means of flow of rock.
•This flow of rock establishes large cells the tectonic plates ride on.
Convection In a boiling pot of water
How convection may drive plate motion
1
Two possible types of convection:
a) Whole mantle
b) Layered convection
The different types of plate boundaries
Normal fault:
Rifts or ridges are
characterized by normal
faults which are extensional.
Reverse fault:
The major fault that
accommodate the motion
between the plate in
subduction si a thrust or low
angle reverse fault. These
faults are compressio nal.
2
Passive margins are the transit ion from continental to oceanic crust
remaining after rifting but it is not a plate boundary
How these plate boundaries
are distributed with relation
to mantle convection.
3
4
Divergent Boundaries
Oceanic P late Separat ion
Volca noes a nd ea rthquake s co ncent rate.
th
Nor
ri c
Ame
e
t
a
l
P
an
MidAt lant ic
Ridge
E ur
as
Pla ia n
te
5
How rifting work on a continent
A) Hot mantle causes crustal
uplift and stretching
accommodated by 1)
normal faults in the brittle
upper crust and 2) ductile
flow in the lower crust.
B) If a successful rift forms
new rock is injected into the
crust by cooling of mantle
rock.
C) This result s in an ocean
basin and passive
continental margins where
the continental crust binds
to the oceanic crust. This
is not a plate boundary, the
ridge is the plate boundary
A triple junction of rifts is the typical configuration of rifts. In order for the
continent to break apart two of the rifts must succeed in developing oceanic
crust. The third rif t may continue to break up the continent or it may stop in
which case a rift is left behind. These usually become the location of a
future significant river valley (i.e. the Mississippi river, the Amazon …)
6
Divergent Boundaries
Continenta l P late Separat ion
Parallel valleys; volcanoes and ea rthq uakes.
East Af rican
Rif t Valley
a
Afr ic
n P la
So ma
te
The fate of the rifts are:
1) Future ocean basins
2) Failed rifts which
typically become
major river valleys.
l i Sub
p la te
Mississippi
Red River
(from an
older even)
Future ocean basins
Congo
Amazon
7
Convergent Boundaries
Ocean-O cean Co nvergen ce
Deep-sea t ren ch; vo lcan ic is land arc.
Mariana Isla nds
e
ipp in
Ph i l
e
Pla t
Marianas T rench
Pa cif
ic
Pla te
8
Convergent Boundaries
Ocean-Co ntinent Conve rgence
A vo lcan ic be lt of
moun tain s fo rms.
Andes
Mountain s
Peru -Ch ile Tren ch
Nazca
Pla te
South
Ame rican
Plate
9
Convergent Boundaries
Continent -Con tinen t Convergen ce
Cru st crumb les, creat ing h igh
moun tain s and a w ide plateau.
Tibetan
Plateau
Hima laya
st
India n -Au
e
ra lian Plat
Main
thru st
fault
Euras ian
Plate
10
11
12
13
Transf orm-Fault Boundaries
Mid-O cean Ridge T ransfo rm Fau lt
Spreading cente rs o ffset.
E ura s
ia n Pl
a te
n Pla te
me rica
North A
14
As plates
move past
each other...
an
S
San
Francisco
A
a
re
nd
…creek beds
are offset
fa
ult
s
Los Angeles
Transf orm-Fault Boundaries
Continenta l T ransfo rm Fau lt
Offset cont inen tal crust.
c
Pa cif i
Pla te
No rth
Ame r
ica
n Pla te
Accretion: Building a continent is accomplished by accretion.
Accretion is the process by which new material is added to the edges
of continents. This material may be new rock material added by
subduction, island arcs developed away from the continents or
fragments of old continents.
15
Craton:
A craton is the ancient core of
the continent. (Archean, older
then 2.5 billion year, and
Proterozoic older than 550
million years). It is made up
of metamorphic rock.
Continents are accreted from
the middle outward.
North America is the best
example of this because it
has only one craton.
Virtually all the other
continents are currently
composed of several cratonic
fragments.
Accretion by the addition of
A buoyant fragment of crust.
This fragment may be:
1) An island arc (an older
one not related to current
subduction)
2) A fragment of a other
continent
3) Hot spot island
4) ?
Accretion of an island arc
related to current subduction
event.
16
Accretion by continent-continent
collision followed by rifting. The
Llano uplift which is the hill
country around San Antonio
and Austin may be a fragment
of Africa which was attached to
North America in this fashion.
Accretion by a transform fault.
Much of Central America and
the Yucatan may have been
accreted in this manor.
The age of accretion of the continents. North America has a single craton.
Most of the other are an assemblage of many cratons.
17
The following frames show the assemblage of the supper
continent Pangaea from a North American perspective.
A SSEMBLY OF PA NGAEA
RODINI A Late P rote rozo ic, 7 50 Ma
Formed about 1.1 billion
years ago; began to break
up about 750 million
years ago.
A SSEMBLY OF PA NGAEA
La te P rote rozo ic, 650 Ma
The pre-Pangean pattern
of continental drift.
18
Laurentia is a old continent that includes North America and Greenland
Taconic island arc
A SSEMBLY OF PA NGAEA
Midd le Ordov ic ian, 458 Ma
The pre-Pangean pattern
of continental drift.
Baltica is now part of Eurasia
19
Baltica
Gondwana is an ancient supper continent that was made up of most of the
modern day southern continents.
A SSEMBLY OF PA NGAEA
Early Devon ian, 39 0 Ma
The pre-Pangean pattern
of continental drift.
20
A SSEMBLY OF PA NGAEA
P ANG AE A (a) Early T rias sic, 237 Ma
Assembled by 237 Ma.
21
BREAKUP OF PANGA EA
(b) Ea rly Ju rass ic, 1 95 Ma
Signaled by the opening
of rifts from which lava
poured; relics can be
found today in volcanic
rocks from Nova Scotia
to North Carolina.
BREAKUP OF PANGA EA
(c) Late Ju rass ic, 152 Ma
BREAKUP OF PANGA EA
(d) Late C retaceous, Early Tertia ry, 66 Ma
22
THE PRESENT-DAY A ND FUTURE WORLD
(e) P RESE NT-D AY WO RLD
THE PRESENT-DAY A ND FUTURE WORLD
(e) P RESE NT-D AY WO RLD
The modern world has
been produced over the
past 65 million years.
THE PRESENT-DAY A ND FUTURE WORLD
(f) 50 million years in the f utu re
23