Plate Tectonics
1
Lecture Outline
Lithospheric plates Plate boundaries
Divergent Convergent Transform
Plate interiors
(This will take ~ 2 classes) The Sinai Peninsula: a fragment of continental crust rifted away from Africa and Arabia.
2
Lithospheric plates ~13 major plates
Fig. 4.3
3
Lithospheric plates ~13 major plates; plate boundaries defined by zones of seismic activity
Fig. 4.5
1
4
Relationship between plate boundaries and continental margins
two types of continental margins:
active margins - correspond with plate boundaries passive margins - do not correspond with plate boundaries
5
Passive continental margin
Mohorovicic discontinuity
Fig. 4.4
Georgia: located on a passive margin CUMBERLAND PLATEAU
6
BLUE RIDGE
BLUE RIDGE VALLEY AND RIDGE
Atlanta
PIEDMONT
(ign + met) GEORGIA COASTAL PLAIN
(sedimentary)
Coastal Plain sediments continue onto the continental shelf, and are underlain by thinned basement rocks similar to those in the Georgia Piedmont.
2
7
Plate boundaries Geologically active
earthquakes volcanism
Fig. 4.6
Three types
divergent convergent transform
Let’s make this more fun…
8
9
TRANSFORM DIVERGENT
CONVERGENT
3
10
Plate tectonics on a Hawaiian lava lake!!
11
Divergent plate boundaries
constructive - crust (lithosphere) is being formed by seafloor spreading geologic activity
voluminous volcanism earthquakes: shallow and not particularly intense
two settings of divergent tectonics
mid-ocean ridges continental rifts
12
Mid-ocean ridges
4
13
Mid-ocean ridges
Fig. 4.8
Pillow lava (basalt)
Eruption of pillow lava
14
15
5
16
Hydrothermal vents (“black smokers�) Fig. 4.10
17
Mid-ocean ridges
Fig. 4.8 Upwelling of solid asthenospheric mantle
18
Example of a mid-ocean rift:
Thingvellir Rift
Iceland
6
19
Example of a continental rift:
Fig. 4.25
East Africa
Mount Kilimanjaro
Continental rifts and the formation of oceans
20
Fig. 4.24
What happens to oceanic lithosphere as it ages? Fig. 4.12
Answer: it cools, thickens, and sinks
21
7
22
Convergent plate boundaries
destructive - crust (lithosphere) is being returned to the mantle by subduction geologic activity
volcanism - less voluminous than at MOR’s, but more of a threat to humans earthquakes - intense, some deep
Subduction zone
23
Fig. 4.14 a
24
various types, depending on the types of crust (lithosphere) involved:
continental crust vs. oceanic crust → oceanic crust is subducted oceanic crust vs. oceanic crust → older (more dense) oceanic crust is subducted continental crust vs. continental crust → neither is subducted; large mountains form
8
25
Subduction along a continental margin Fig. 4.15 a
~100 km
introduction of H2O into the mantle lowers its melting temperature, making basaltic magma
26
Example of a continental volcanic arc (modern):
Cascades
Mount St. Helens
27
Example of a continental volcanic arc (ancient): vo acc
fo r
arc n n ic asi sm lc a cb p ri ear ary io n re t
California
9
28
Example of a continental volcanic arc (modern):
Andes Machu Pichu, Peru Nazca Plate
Subduction along an oceanic island arc
South American Plate
29
Better than Fig. 4.15b
Examples of oceanic island arcs: Aleutians, Japan, and Phillippines
30
Mount Fuji
10
The Pacific “Ring of Fire”
Continental Collision
31
32
Fig. 4.27
Continental Collision
33
Fig. 4.27
11
An ancient suture in the Appalachians
34
ancient pillow basalts Fig. 3.6 b
Suture formed by closure of Iapetus Ocean (proto-Atlantic) when Pangea was forming
Example of a continental collision:
35
Himalayas
Mount Everest
Example of a continental collision:
36
Himalayas
Mount Everest
12
37
Transform plate boundaries
neither constructive or destructive geologic activity
intense earthquakes generally no volcanic activity
on the continents, they are long faults in the oceans, they segment the oceanic ridges
Example of a transform plate boundary:
38
San Andreas Fault
Example of a transform plate boundary:
39
Fig. 4.19
San Andreas Fault
13
40
Oceanic fracture zones European Plate North American Plate African Plate
South American Plate
An old idea about fracture zones
41
R EJ
! D E EC T Ridge
Ridge
Similar to Fig. 4.17 a-d
A newer idea about fracture zones
42
Ridge
Similar to Fig. 4.17 a-d active transform faulting here no active faulting
Ridge
no active faulting
14