American geological practice: Participation and examination. Part 1. Origin of REE-enriched hematite breccias at Olympic Dam, South Australia. Part 2. The rejection of continental drift

REE-enriched hematite breccias are the host rocks to over two billion tons of Cu-U-Au-Ag ore at Olympic Dam, South Australia. The breccias form a steeply-dipping network of breccia dikes within a fractured granite host. Field and petrographic relations indicate that the breccias formed primarily by extreme mechanical fragmentation and intense hydrothermal alteration of the wall rock granite. The hematite breccias are highly enriched in rare earth elements (REEs), with typical La values of 10;Embedded within this study--and within all scientific research--are questions about the nature of scientific evidence and tensions surrounding the selection of appropriate methods. In geology, an important example is the conflict between field- and laboratory-based science. The sources and development of this tension are the subject of the second half of this dissertation, The rejection of continental drift. Among geologists and historians, the rejection in the 1920s of Alfred Wegener's theory of continental drift has been generally attributed to a lack of an adequate causal mechanism. But several earth scientists in the 1920s and '30s proposed both dynamic and kinematic explanations of drift, of which the most widely discussed was the Joly-Holmes theory of subcrustal convection. Continental drift was rejected because of a conflict over the nature of geological evidence, and the proper relationship of evidence to theory. The early evidence of continental drift consisted of homological data obtained in the field: similarities of faunal assemblages, stratigraphic sequences, and coastal morphologies across widely separated continents previously contiguous. These homologies became the source of debate--particularly in the United States--over the reliability of geological field data. In an effort to minimize the element of personal judgment involved in their interpretation, many American geologists were interpreting homological data according to a uniformitarian doctrine which required geological theory to be derived by close reference to observable processes. The theory of drift appeared to threaten this cherished methodological practice. The resolution was a rejection of the theory, rather than a modification of practice, until plate tectonics was instantiated by means of a different kind of data, whose relationship to geological practice was being newly-formed.