Mid-ocean
ridges have segmented architectures. The underlying processes
differ somewhat in fast- and slow-spreading centers, but
in general, first-order segments are hundreds of kilometers
long, persist for millions to tens of millions of years
and are bounded by relatively permanent, rigid-plate transform
faults. First-order segments are divided into several
second- or third-order segments, bounded by a variety
of nonrigid discontinuities. These smaller segments lengthen,
shorten, or even disappear in 10 million to 100,000 years,
respectively. At the finest scale, fourth-order segments,
about 10 kilometers long, may survive for only 100 to
10,000 years. These segments are the products of dike
intrusion events, the fundamental units of crustal creation.[back]
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