R. W. Shepherd writes:
In 1905, German geologist Gustav Steinmann identified a succession of basal serpentinite, basalt, and deep water sedimentary rocks at a continental location known as Steinmann’s Trinity. Layered cumulate ultramafics and layered gabbros have been added to Steinmann’s original association of rocks, now known by the term “ophiolite” and derived from the Greek word “ophis“ meaning snake.
Ophiolites are interpreted to be fragments of ocean floor sheared off from subducting crust, caught between colliding continents, and elevated to a continental location.
Ophiolites have great geological significance for two reasons:
1: This association of rocks provides direct access to samples of ocean crust and upper mantle; and
2: The oldest ocean crust is dated at approximately 200 million years so dating of ophiolites which are significantly older than the oldest ocean crust provides evidence for long term operation of plate tectonics mechanisms and seafloor spreading.
The Betts Cove ophiolite was identified in the 1960s by J.F. Dewey and J.M. Bird of the State University of New York, and by graduate student Robert Stevens of Memorial University, amongst others, as the remains of ancient ocean crust. This ophiolite was one of the first confirmations of the 1966 hypothesis of the University of Toronto’s J. Tuzo Wilson relevant to plate tectonic activity, seafloor spreading, and the Wilson cycle.
Exposed crust – lithosphere contact at Table Mountain, Gros Morne National Park, Newfoundland.