Introduction:

"Exotic terranes" - the very name conjures up a sense of mystery and foreign intrigue. Bounded by major faults, each terrane is a geologic province unto itself, with a unique geologic history and features that differ sharply from those of its neighbors. For years geologists puzzled over abrupt changes in geology and paleobiology, peculiar formations of ore deposits, and just how to explain rock assemblages from decidedly different backgrounds being found next to one another. How could these huge pieces of continental and oceanic crust be where they are if it was clear they did not originate in that location? Some background information is helpful:

Discovery Timescale:
1912
Alfred Wegener, a German scientist trained in astronomy, applies his scientific and curious mind to the geologic puzzle of the placement of the continents. By geographically aligning plant and animal fossils found only in specific land areas and from specific time periods with one another, Wegener contended the continents must have been together in a certain configuration about 200 million years ago. Simply put, Wegener proposed that the continents float on the denser underlying Earth, and that the very shapes of the continents imply they once fitted together. He called this super continent Pangea, and the process responsible for moving the land masses across the surface of the planet continental drift. But Wegener's theories were not fully accepted by his contemporaries, and his ideas lay relatively dormant for decades.

1950
M. L. Thompson, Harry E. Wheeler, and W. K. Danner determine the fusulinids found in the Cache Creek Terrane of British Columbia are identical to those found in Asia but completely different from the fusulinids found in the interior of the North American craton. The work begins to determine just how this could occur.

The '60's
In the 1960's, research into paleomagnetic signatures of volcanic rocks which make up the ocean floor lead scientists to hypothesize that these patterns were the result of repeated reversals in the Earth's magnetic field. Using potassium-argon techniques (another great product of the '60's!), scientists were able to date and correlate magnetic striping patterns for the world's ocean floors, confirming the process of ocean floor spreading. Now we have a mechanism for movement on the Earth's crust! AND we have renewed interest in Wegener's theory. Briefly, as sea floors form, they are moved away from the magma source by the next "batch" of rising magma. As they move away, they cool, become denser, sinking and ultimately subducting under the less dense continental crusts with which they collide. They move, driven by the earth's heat, much like a conveyor belt. In 1968, J. Tuzo Wilson proposes his super-continent cycle theory based on the formation and destruction patterns of ocean basins.

1970

The United States Geologic Survey (USGS) sends a team of geologist to Alaska to survey for mineral resources. But the normally reliable prediction techniques do not work, and by using paleomagnetic signatures, biostratigraphy and other dating tools, the team finds Alaska to be made up of crustal pieces originally from the ocean which preceded the Pacific. A new area of geologic study begins in ernest!


1980 to present
Expert plate tectonocists David L. Jones, Allan Cox, Peter Coney and Myrl Beck, write that most of the exotic terranes that have been identified are of ocean origin and consist of oceanic lithosphere that once included volcanic islands, plateaus, seamount chains, ridges, or island arcs. Some represent fragments of continents. Technical advances - satellites, sonar, radar, and immense amounts of data for computer manipulation and modeling - have yielded a better understanding of plate boundaries, convergent and divergent zones, and super continent cycles.

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