120 | Great Geologists
STAGE EXAMPLES DOMINANT MOTIONS CHARACTERISTICS
Embryonic East Africa Rifts Uplifts Rift valleys
Young Red Sea, Gulf of Aden Spreading Narrow seas with parallel coasts
and central depression
Mature Atlantic Ocean Spreading Ocean basin with active mid-ocean
ridges
Declining Pacific Ocean Shrinking Island arcs and adjacent trenches
around margins
Terminal Mediterranean Sea Shrinking Young mountains and uplifts
Relic Scar (Geosuture) Indus Line in the Himalayas Shrinking and uplifts Young mountains
Simplified version of the Wilson Cycle.
necessarily mean that they were formed
close together or that the sediments
lying on one province were derived
from the province now besides it.” By
1963, he was contributing actively to the
development of plate tectonic theory with
a remarkable series of papers that linked
apparently unrelated processes such
as ocean basin formation (rifting) and
mountain building (convergence) into a
connected dynamic model.
stable core of a mantle convection cell.
As the Pacific lithospheric plate moves
across this fixed source, older islands of
the chain are carried ‘downstream’. This
in turn allows for the determination of
velocity of plate movement relative to the
hot spot.
In 1965, he followed this discovery with
the idea of a new type of plate boundary,
transform faults. These faults slip
horizontally, connecting oceanic ridges
His first key paper relaterd to plate
(divergent boundaries) to ocean trenches
tectonics explained the presence of
(convergent boundaries). Transform faults
volcanoes, such as the Hawaiian Islands, were regarded as the missing piece in
far from mid-ocean ridges. Such island
the puzzle of plate tectonic theory. They
chains are young compared with the
allow for plates to slide past each other
continents, but show a trend towards
without any oceanic crust being created
older ages with increasing distance from or destroyed. Wilson’s recognition of
a mid-ocean ridge. This suggests ocean- these features stemmed from a winter
floor spreading from these ridges, driven term spent at the University of Cambridge
by mantle convection currents. But why
where he was able to spend time in the
the volcanic activity in these remote
company of some of the other great plate
islands? Wilson proposed that the source tectonic pioneers: Bullard, Vine, Mathews
of volcanic rock for the Hawaiian Islands is and Hess.
a plume rising from a ‘hot spot’ within the
Wilson then turned his attention to the
life history of oceans and in particular
the repeated cycles of ocean opening
and closure that must have occurred
through geological time. Noting that no
pre-Mesozoic ocean crust now exists in
situ, he recognised that ocean formation
and destruction must be sought indirectly
through the identification of suture
zones. The Earth’s oceans could be
categorised in terms of their stage of
maturity within a life-cycle, beginning
with rifting and ending with accretion
as continents converge, then rifting
once again. This supercontinent cycle
is now usually described as the Wilson
Cycle and, although further developed
by subsequent workers, remains
the fundamental description of the
consequence of plate tectonics.
Wilson’s renunciation of his opposition to
continental drift and mantle convection
and his subsequent championing of plate
tectonic theory is a wonderful example
of the openness of mind that great