Earth’s major plates. Note: Boundaries rarely correspond to the contact between oceans and continents! . Types of plate boundaries. Relation between igneous activity and plate boundaries. Starting point: Continents and oceans are the pieces of an eden broken up by the great flood:.
Note: Boundaries rarely correspond to the contact between oceans and continents!
Starting point: Continents and oceans are the pieces of an eden broken up by the great flood:
1: The earth is divided into continents and oceans
Alfred Wegener, ca. 1920,
in a weird hat.
2: The continents look like pieces of a puzzle, and share elements of their geology.
3: The distribution of fossil animals and plants re-enforces the tie-points between the continents
that the continents were
once connected but have
drifted apart by ‘sliding’ over
or ‘plowing’ through the ocean floor
Driving force: mystery, or
centrifugal force, or both
This is just stupid
Any force strong enough to ‘push’ a continent over a bed of ocean floor would internally deform the continent instead
Not all pieces of the continental puzzle really match
Many continental margins don’t even fit geometrically
Even if they fit, so what! Lots of ‘fits’ are possible just by chance
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.
Wagener was only partially correct. The ring of fire is a locus
of faulting, but there are other loci not expected if continents drift
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.
Centered on most great belts of seismicity, and
is rare elsewhere
(in mysterious units
— 10,000 ’s)
north magnetic pole, based on records from North American rocks
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’.
Much more important is an incredibly subtle detail to the fine structure of the modern magnetic field…
(I.e., relative to long-wavelength field)
magnetic rocks in the crust
A magnetic ‘reversal’ occurs between these two times
eruptions on the sea floor.
1: Collecting samples with the Glomar Challenger
0.01167 % of natural K
e- emission; = 4.982x10-10 yr-1
e- capture; e = 0.581x10-10 yr-11
= e + = 5.543x10-10 yr-1
40Ar = e/40K(et-1) + 40Ar0
Amphibole: 500 to 700 ˚C
Biotite: 300 to 400 ˚C
K-feldspar: 200-250 ˚C
magnetic stripes is complete:
Implied rates of plate divergence, convergence and strike-slip motion