A controversy in science : the debate about allochthonous terranes on the west coast of North America

• Main Author: Sharpe, Adrian Patterson
• Format: Master Thesis
• Language: unknown
• Published: 1991
• Subjects: Geology; stratigraphic; North America; Plate tectonics; Arctic; Arctic Ocean; Canada; Pacific; British Columbia; Andreas; Beaufort Sea; Brooks Range; Tundra; Alaska
• Online Access: http://hdl.handle.net/11343/114087

Someone has unkindly called the west coast of North America the `garbage dump' of the Pacific Ocean. This description is a bizarre way of describing what is currently the view of many geologists, mostly from the west coast of North America, of the geological composition of the continent west of longitude 111e. This they believe to be approximately the boundary of the American craton dating back to Pre-Cambrian time. Everything to the west, according to some researchers, has been accreted to the craton since the Paleozoic era. At the start of the 1970s, the geological community had barely had time to get used to the new version of continental drift, plate tectonics, before some geologists began to make suggestions about the far-travelled nature of some rock assemblages on the west of the American continent. Since that time controversy has developed amongst geologists about these claims. This is the subject of this thesis: the debate about allochthonous terranes in western North America, a debate sparked by a group of researchers at Menlo Park, the Western Region office of the U.S. Geological Survey. At the northern end of the continent, a vast stretch of tundra fronting the Arctic Ocean and Beaufort Sea is backed by the towering Brooks Range. This range of mountains acts as a backstop to the ranges which cover the rest of Alaska as they have been puslied northwards by crustal movement. In this sort of terrain, which is also found in British Columbia, reconnaissance mapping and geological research is expensive and arduous, not to mention dangerous. It is only possible in certain parts of the year and involves the use of expensive equipment such as helicopters. Only such institutions as the Geological Surveys of the United States and Canada or oil and mining companies are able to fund such research. Academic institutions do not usually have the resources for it. This is no doubt one of the reasons for the co-operative efforts between the academic community and the richer institutions, which are a part of this story about alldchthonous terranes. From Alaska to Oregon, the Pacific coastline is punctuated by over 1000 rivers which have their source in the Cordillera mountains. The Cordilleras themselves are made up of a number of mountain ranges including the Rocky Mountains, the Coast Ranges, the Cascade Range and the Sierra Nevadas. Between the Rockies and the Sierra Nevadas lies the Great Basin. This Basin and Range area is the setting for the story of plate tectonics and terranes. To the west of the Sierra Nevadas lies the "Franciscan" and the San Andreas fault area --the histories of which have also provided material for lively discussion. This enormous tract of land in western. North America is argued to be a melange of diverse fragments, many of which started their journey as ocean floor extrusions at the junctions of two or more plates of lithosphere in the Pacific Ocean (Tillotsen and Walker, eds.,1983), then moved to their present locations over hundreds of millions of years (Jones et al., 1982). Chapter One outlines the work done by the pioneers of "terrane science", who made the first tentative suggestions at the beginning of the 1970s about the foreign character or allochthoneity of terranes in western North America. Mention is made of some of their precursors and some landmark publications are examined. The chapter concludes with some reflections on the adequacy of modern philosophy of science in accounting for the issues raised by the terrane debate and whether or not it is possible to separate the cognitive from the social issue's in the evolution of scientific theory. Chapter Two examines the work done in the decade between the 1970s and the 1980s and the attempt by a group of geologists to introduce a "new" concept into the prevailing global theory of plate tectonics. At the conclusion of this chapter there is an overview of the dynamics of theory change and the rhetoric employed by the proponents and opponents of that concept. Chapter Three considers the views of a group of geologists who oppose the terrane concept as it is practised. Their comments form the basis for determining the depth and extent of opposition within the geological community to "terrane science". The final chapter presents an overview of the factors involved in the polarization of a scientific community when a "hot topic" arises. The conclusion, judging by the opinions of the scientists involved, is that "terrane science" is a relatively minor corollary of plate tectonics theory which has been over-determined by the rhetoric and style of a group of scientists, the "California group", who have social "interests" in a push for hegemony in geology. However, the history of terranes in the 70s is not simply a story about "interests" and this chapter outlines the ways in which cognitive and social elements are inextricably interwoven in the development of a science.