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paper_3 - 3 Structural terms including fault rock terms...

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KHB Page 1 1/29/2007Paper_3.doc 3. Structural terms including fault rock terms Recommendations by the IUGS Subcommission on the Systematics of Metamorphic Rocks. Web version of 01.02.07 Kate Brodie 1 , Douglas Fettes 2 , Ben Harte 3 and Rolf Schmid 4 1 Department of Earth Sciences, University of Manchester, UK 2 British Geological Survey, Edinburgh, UK 3 School of Geosciences, University of Edinburgh, UK 4 ETH-Centre, Zürich, Switzerland 5B Introduction A Study Group (SG), under the leadership of K. Brodie, was set up to look at nomenclature relating to structural terms. At an early stage a questionnaire was sent to around 60 structural geologists throughout the world, with a series of initial definitions. The response did much to guide the work of the SG and the SCMR in finalising its recommendations. 0B Background Many of the definitions given below were adopted by the SCMR without difficulty; others gave rise to considerable debate. Problems arose for a variety of reasons, namely: the variable usage of terms across the geological community (e.g. gneiss and schist); terms such as slate and cleavage proved difficult because there are no similar terms in many non-English speaking countries; equally, the difference between cleavage and schistosity and the use of texture and microstructure proved major sticking points. In other cases it was difficult to differentiate between rock types solely on features observable in the field at hand-specimen scale or in thin section examination as required by the SCMR scheme (Schmid et al., this vol.). Also, although the SCMR scheme seeks to avoid terms based on processes wherever possible, this was not practical with many terms related to fault rocks (e.g. mylonite and cataclasite). The following sections discuss the main problem areas and the basis that the SCMR used in deciding on its recommended definitions. www.bgs.ac.uk/scmr/home.html
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