Page 102 - Global Tectonics

SEA FLOOR SPREADING AND TRANSFORM FAULTS 89

Figure 4.18 Northern termination of the Mid-Atlantic Ridge (redrawn from Wilson, 1965, with permission from Nature
207, 334–47. Copyright © 1965 Macmillan Publishers Ltd).

re-interpretation, as ridge–ridge transform faults (Fig. passes through Iceland, and terminates southwest of
4.15a), implies that the offsets on them do not change Spitsbergen at the De Geer Fault. This dextral ridge-
with time. Thus the geometry, or locus, of the step-like ridge transform fault connects to the Gakkel Ridge in
ridge crest-transform fault sequence in the equatorial the Arctic Basin. Wilson predicted that this is a very
Atlantic has remained essentially unchanged through- slow spreading ridge that is transformed into the Verk-
out the opening of the South Atlantic. As a result the hoyansk Mountains of Siberia by rotation about a
locus parallels the continental shelf edges of South fulcrum near the New Siberian Islands (Fig. 4.18

America and Africa and reflects the geometry of the inset).
original rifting of the Gondwana supercontinent in this
area.
Wilson (1965) also suggested examples of transform 4.2.3 Ridge jumps and
faults in the extreme North Atlantic area (Fig. 4.18). In
early Paleogene times the Mid-Atlantic Ridge bifurcated transform fault offsets
to the south of Greenland. The western branch, which
is now inactive, passed through Baffin Bay and termi- The different offsets observed across the Murray Frac-

nated against the Wegener Fault, an extinct, sinistral ture Zone from magnetic lineations (Fig. 4.1) are
ridge–ridge transform fault. The active eastern branch thought to be due to a change in location of the ridge