Geoscience Reference
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Figure 10.1. A deep reflection line shot by COCORP across the Wind River
Mountains in Wyoming, U.S.A. Heavy lines, thrusts and faults. Shading, sediments.
Short dashed lines, possible multiples. Dotted line at 10 s, an enigmatic
low-frequency event. Event at ∼15 s beneath Green River Basin, a possible Moho
reflector. Dashed line at 4.0-4.5 s, the reflection from the base of the Green River
Basin sediments. This is cut off by the Wind River Thrust. (After Brewer et al .(1980).)
straightforwardly; however, we do have the questionable advantage that no one can
prove us wrong. Academics need not go bankrupt through their misconceptions.
The deepest hole drilled into the crust is in the Kola peninsula of northwestern
Russia. Drilling there began in the early 1970s and has penetrated, so far, to some
13 km. The second deepest hole, 9.1 km, has been drilled in Germany, the KTB
project. Technically, drilling such holes is an exceedingly difficult enterprise. One
of the problems with deep seismic-reflection profiling (see Section 4.5.5) is that
differing interpretations of the various reflectors can sometimes be made. Nev-
ertheless, deep seismic profiling is very successful and has given an immediate
solution to some geological puzzles; for instance, it enabled COCORP to trace the
Wind River Thrust as a 30-35 dipping reflector in Wyoming (U.S.A.), from its
surface exposure to some 25 km deep (Fig. 10.1), and to learn without doubt that
compressional rather than vertical forces were the cause of the uplifted basement
blocks.
Geochemistry is probably less hindered than structural geology by our inability
to obtain deep, fresh samples - although, of course, the exact composition of the
lower crust and the nature of the Moho and upper mantle are matters of current
debate, which fresh samples could resolve.
In this chapter some of the major geophysical and geological features of the
continents are described and discussed in terms of their relation to the internal
processes of the Earth.
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