Geoscience Reference
In-Depth Information
Most geologists, not being seismologists, likely did not read their article, but
few missed seeing the iconic block diagram that accompanied it, which presented
“all you need to know about plate tectonics” in one view. It showed how plates
collide, slip past each other, and descend along subduction zones.
mology and the New Global Tectonics,”
Journal of Geophysical Research
73, no. 18 (1968).
Morgan intended his 1968 paper to present “A geometrical framework with
that plate tectonics is a geometrical or “kinematic” theory: it describes
how
plates
move, not
why
they move. That they do move was now self-evident, relegating the
decades-old bugaboo of “lack of a mechanism” to a secondary issue.
Riding Piggyback
Now we come to the connection between continental drift and plate tectonics.
Some plates contain only ocean basin, others contain both ocean basin and contin-
ents. As the plates move, those that contain continents carry them along. Instead
of sialic continents having to plow through a sea of denser sima, to use the older
terms, the continents ride atop the plates.
But could plate tectonics also explain the large-scale features ofcontinental geo-
logy? In his 1966 paper in
Science
, Fred Vine showed the answer was likely to be
yes:
I suggest that, to a first-order approximation, the more recent geologic history and structures
of the western United States can be ascribed to the progressive westward drift of the North
American continent away from the spreading Atlantic Ridge, and to the fact that the continent
has overridden and partially resorbed first the trench system and more recently the crest of the
East Pacific Rise.
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In 1970, Tanya Atwater worked out the details, demonstrating how the
westward-drifting North American continent had overridden and swallowed up a
trench that had once existed off western North America. Not only a trench but also
an entire plate had vanished like Atlantis underneath the titanic American plate,
