Environmental Engineering Reference
In-Depth Information
Figure 10.10
Two stages in continental collision. The
convergence of two continents has almost closed the
intervening ocean basin (a) leading to continental collision,
A-subduction, folding and faulting (b). Ophiolite nappes
(striped) lie along the suture; key otherwise as for
Figure
10.8.
through drag effects, in adjacent lithosphere. New Zealand is transected by active strike-
slip B-subduction at the Pacific/Indo-Australian plate boundary. The San Andreas fault
system of California, triggered where the East Pacific Rise (mid-ocean ridge) comes
onshore, is moving San Francisco and Los Angeles slowly together (Plate 10.1). The
Great Glen fault in Scotland displaced what is now the Scottish north-west highland zone
300 km south-west during the Palaeozoic. The many oblique, as well as headon,
movements at convergent plate boundaries determine that
accretionary tectonics
incorporate slivers and flakes of
suspect
or
displaced terranes
, including ophiolites far
removed from their sea-floor origins.
OROGENS
Plate convergence creates major
orogens
or narrow, linear
cordilleran mountain
systems - literally, 'chords' of sub-parallel ranges and inter vening basins reflecting
substantial crustal deformation. The origin and dynamic character of major examples are
explained in Chapter 25. Annual uplift rates of 10-20 mm yr
−1
may seem modest but
would amount to several thousand metres if sustained for just 1 Ma. Modern Cenozoic
orogens represent later stages of the post-Pangaea super-continental cycle and many
experience rapid uplift, stimulating vigorous erosion as endogenetic and exogenetic
forces converge (Figure 10.11 and Colour Plate 6 betwen pp. 272 and 273). They are
