Geoscience Reference
In-Depth Information
Figure 10.25.
(a) A line
drawing of the 15-fold
unmigrated
deep-seismic-reflection
profile DRUM shot off the
northern coast of
Scotland (see also Fig.
4.46). (b) Details of the
reflections from the
Flannan Thrust. (c) Details
of the reflections from the
sub-horizontal
deep-mantle reflector.
(From McGeary and
Warner (1985) and Warner
and McGeary (1987).)
supports the implication that there is a major detachment surface at this level.
The maximum uplift in the Alps is 0.15 cm yr
−
1
, almost an order of magnitude
less than Himalayan values.
Ancient continental collisions
Interpreting ancient continental collision zones is a complex geological
problem - tectonics and erosion mean that only parts of the jigsaw remain for
study.
The
Caledonian orogeny
occurred some 400 Ma ago when the ancient Iape-
tus Ocean between North America and Europe closed during the formation of
the supercontinent Pangea (Fig. 3.30). The remnants of this collision are now
in Scotland and eastern North America. The Flannan Thrust off the northern
coast of Scotland has been spectacularly imaged by deep-seismic-reflection
profiling (Fig. 10.25). This thrust originates in the lower crust, cuts (and may
offset) the Moho and extends to a depth of 75-85 km. The upper crust is charac-
terized by rotated half-grabens filled with sediment, which formed during a later
period of Mesozoic extension. The lower crust is highly reflective, with the Moho
clearly visible as a bright reflector at its base. The dipping crustal reflector which
