Geoscience Reference
In-Depth Information
all the facts of observation,” and the magnetic anomaly patterns in the northeastern
Pacific “may have been generated by other mechanisms.”
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If a scientific revolution had broken out, the front-line troops, the geophysicists,
had gone AWOL, and someone had forgotten to rouse the geologists.
Juan de Fuca
Using their computer program and the preliminary magnetic-reversal timescale
availablein1963,VineandMatthewshadbeenabletoreproducethegeneralshape
of the magnetic anomaly patterns across the Carlsberg and Mid-Atlantic ridges,
though not the details. In 1965, Vine and the Canadian geologist Tuzo Wilson, on
leave at Cambridge at the time, decided to take the next step to see whether the
latest paleomagnetic timescale would allow them to reproduce more closely the
magnetic patterns on either side of a ridge. They chose the Juan de Fuca Ridge off
Vancouver Island in the Pacific Northwest, which Wilson had recently discovered
and named. The discovery resulted from a morning conversation between Wilson,
Hess, and Vine as Wilson was developing his “transform fault” idea, to be dis-
cussed shortly. Wilson's thinking suggested that there “should be a ridge” in a cer-
tain sector of the northeastern Pacific. Hess replied that if so, “there ought to be
the library, found the map, and located the previously undiscovered ridge. He also
noticed that the north-south magnetic anomalies on either side of the ridge were
cesses like the extrusion of basalt lava along a spreading ridge are not supposed to
yield such regular results.
Vine and Wilson now began to try to replicate the observed magnetic anomalies
across the Juan de Fuca Ridge using their computer model. Since they had no way
of knowing how fast the seafloor spread, they had to proceed by trial and error,
substituting different spreading rates until theygotsomething approaching amatch
between the observed and modeled patterns. A spreading rate of about 1.5 centi-
meters per year on either side of the ridge brought the two into close, though not
perfect, concordance. The imperfection led Vine and Wilson to conclude that “the
“the problem was that we couldn't interpret the anomalies in terms of a confident
spreading rate. We couldn't do that because we didn't have the right time scale.
Had Itaken the big jump and insisted oninterpreting it at a constant spreading rate,
it would have been considered too outrageous at the time.”
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