![Page 1: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/1.jpg)
Earth’s major plates
Note: Boundaries rarely correspond to the contact between oceans and continents!
![Page 2: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/2.jpg)
Types of plate boundaries
![Page 3: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/3.jpg)
Relation between igneous activity and plate boundaries
![Page 4: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/4.jpg)
Starting point: Continents and oceans are the pieces of an eden broken up by the great flood:
![Page 5: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/5.jpg)
1: The earth is divided into continents and oceans
Alfred Wegener proposes continental drift ca. 1912
Alfred Wegener, ca. 1920,in a weird hat.
![Page 6: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/6.jpg)
2: The continents look like pieces of a puzzle, and share elements of their geology.
![Page 7: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/7.jpg)
3: The distribution of fossil animals and plants re-enforces the tie-points between the continents
![Page 8: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/8.jpg)
4: The edges of the continents are locations of faultingand seismicity
![Page 9: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/9.jpg)
5: when continents rift apart, you find an ocean
between them
RiftHorst Graben
![Page 10: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/10.jpg)
Put it all together, and seethat the continents were once connected but have
drifted apart by ‘sliding’ overor ‘plowing’ through the ocean floor
Driving force: mystery, or
centrifugal force, or both
![Page 11: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/11.jpg)
Counter-arguments
This is just stupid
Any force strong enough to ‘push’ a continent over a bed of ocean floor would internally deform the continent instead
![Page 12: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/12.jpg)
Counter-arguments
Not all pieces of the continental puzzle really match
![Page 13: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/13.jpg)
Counter-arguments
Many continental margins don’t even fit geometrically
![Page 14: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/14.jpg)
Counter-arguments
Even if they fit, so what! Lots of ‘fits’ are possible just by chance
![Page 15: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/15.jpg)
Breakthrough:
Harry Hess and the exploration of the ocean floor
• Led to discovery that the ocean floor is the active part of the plate system, not the passive medium through which continents move.
A ridge
![Page 16: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/16.jpg)
A ridge and its transforms seen in plan view
![Page 17: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/17.jpg)
Ahh, trenches
![Page 18: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/18.jpg)
The real story with seismicityWagener was only partially correct. The ring of fire is a locus
of faulting, but there are other loci not expected if continents drift
![Page 19: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/19.jpg)
And, the seismicity at the edges of the ring of fire don’t represent continents sliding over oceans; they are places where ocean floor plunges
into the deep earth interior.
Benioff-Wadati zones
![Page 20: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/20.jpg)
Centered on most great belts of seismicity, andis rare elsewhere
Active Volcanism
![Page 21: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/21.jpg)
Terrestrial Magnetism
![Page 22: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/22.jpg)
Intensity(in mysterious units
— 10,000 ’s)
Dip
![Page 23: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/23.jpg)
Preservation in rocks of the orientation of the magnetic field
![Page 24: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/24.jpg)
Variation through time of the apparent location of thenorth magnetic pole, based on records from North American rocks
![Page 25: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/25.jpg)
Phanerozoic records of magnetic polar wander from Europe and North America disagree…unless they have moved relative to each other (or, the
shape of the Earth’s magnetic field has varied)
Interesting, but all it really does is support and ‘flesh out’ Wegener’s view of ‘continental drift’.
![Page 26: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/26.jpg)
Much more important is an incredibly subtle detail to the fine structure of the modern magnetic field…
![Page 27: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/27.jpg)
A closer look…
MeasuredAnomaly
(I.e., relative to long-wavelength field)
![Page 28: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/28.jpg)
The anomalies represent positive and negative interference frommagnetic rocks in the crust
A magnetic ‘reversal’ occurs between these two times
![Page 29: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/29.jpg)
How do we know? We’ve seen them appear after volcaniceruptions on the sea floor.
![Page 30: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/30.jpg)
Some real examples
![Page 31: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/31.jpg)
Calibrating the ocean floor’s ‘strip-chart recorder’
1: Collecting samples with the Glomar Challenger
![Page 32: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/32.jpg)
K-Ar dating
40K
40Ca 40Ar88.8 % 11.2 %
e- capture; e = 0.581x10-10 yr-11e- emission; = 4.982x10-10 yr-1
40Ar = e/40K(et-1) + 40Ar0
= e + = 5.543x10-10 yr-1
0.01167 % of natural K
![Page 33: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/33.jpg)
Some ‘closure temperatures’ w/r to K/Ar dating:
Amphibole: 500 to 700 ˚C
Biotite: 300 to 400 ˚C
K-feldspar: 200-250 ˚C
![Page 34: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/34.jpg)
Use in dating magnetic reversals
![Page 35: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/35.jpg)
Maps of magnetic ‘stripes’
![Page 36: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/36.jpg)
Sometimes it’s fun to pretend that our record of the seafloor’smagnetic stripes is complete:
![Page 37: Earth’s major plates Note: Boundaries rarely correspond to the contact between oceans and continents!](https://reader031.vdocuments.us/reader031/viewer/2022032706/56649de55503460f94ade08d/html5/thumbnails/37.jpg)
Implied rates of plate divergence, convergence and strike-slip motion