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University of Toronto - III

In 1985 Tuzo settled happily into a modest office at the University of Toronto, prepared to turn his attention again to global tectonics, to writing his autobiography, and to investigating aspects of the history of exploration in Arctic Canada. He still held one academic position, largely ceremonial: from 1983 to 1986 he was Chancellor of York University.  More than 20 years had passed since the early days of plate tectonics. Tuzo acknowledged the progress that had been made, but his writing from this period gives the impression that he felt that important aspects were being overlooked. He returned to the study of hot spots, which in the interim had been actively pursued by others. Following Crough (1983), he accepted the view that rifts themselves may result from the coalescing of lithospheric fractures radiating from uplifts over hot spots and extended this (109) to investigate the consequences of continents over-riding rifts. A quotation from this paper will illustrate his view on the progress of global tectonics:

Collisions between ridges and coastlines may occur at a variety of angles, including cases where ridges are parallel to coastlines, oblique to them, or at right angles. The consequences of different angles vary so much that failure to consider these differences seems to have been a major cause of deficiencies in tectonic theories.

He proceeded to give the consequences, with examples current and past, of these collision types. They include (respectively parallel, oblique and perpendicular): thrust mountains (the Cordillera of western Canada); coastal shearing leading to transported terranes (Gulf of California); and continental uplift and rifting (Gulf of Aden). Tuzo's fascination with the entry of the East Pacific Rise into the Gulf of California led to an ongoing difference of opinion with some American earth scientists. The conventional view was that the Rise was terminated by the San Andreas transform fault, and thus by Wilson's own rules could proceed no farther into the continent. But Tuzo countered that the rules applied only within the lithosphere and that deeper upwelling of hot mantle material, equivalent to an extension of the East Pacific Rise, could persist under the continent as far as the thermal region of Yellowstone. It was a disagreement largely unresolved at his death, but Tuzo remained convinced of his model. One of his last papers (115) proposed that rich gold deposits in Nevada (known to be fourteen million years old) formed at the very time that portion of the continent passed over the Yellowstone plume.