Department of the Interior, U.S. Geological Survey
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Thrust sheets that underlie the Greenville quadrangle in northeastern Georgia and in northwestern South Carolina have been selectively metamorphosed and deformed during several Paleozoic prograde metamorphic events.
Deformation Quadrangle, 1n the Stensgar Mountain Stevens County, Washington By James G. Evans Abstract Most deformation of the Middle and Late Proterozoic (Deer Trail and Windermere Groups) and Lower Cambrian (Addy Quartzite and Old Dominion Limestone) rocks in the Stensgar Mountain quadrangle occurred during the Mesozoic (pre-Late Jurassic, possibly Early Jurassic or Triassic), in con- nection with duplex thrusting. The principal deformation occurred in stages that generally involved: (1) thrusting, (2) penetrative dynamothermal metamorphism in the greenschist facies, and (3) renewed thrusting. The initial thrusting may have included formation of the duplex fault zone, moderate tilting of the sedimentary and volcanic rocks, and possibly low-grade metamorphism. The dynamothermal metamorphism resulted in development of a slaty cleavage that dips steeply west, as well as numerous minor and a few large folds that plunge at low to moderate angles, generally north. The folds have axial planes parallel to cleavage. Clasts in conglomerates were flattened parallel to cleavage, and their long axes were aligned north-northeastward, subparallel to fold axes. This extension direction parallels the trend of the Kootenay arc, a relation not typical of orogenic belts. The dynamothermal metamorphism included coaxial compressive pulses separated by periods of stress relaxation. The penetra- tive deformation could have been accompanied by slip on preexisting faults, including a large strike-slip component for the roof (Stensgar Mountain thrust) and floor (Lane Mountain thrust) thrusts of the duplex fault zone. Later movements along these roof and floor thrusts and connecting splays are suggested by nonfolded traces of the faults and the faulted, dynamothermally metamorphosed cataclasite adjacent to the Lane Mountain thrust. The penetrative deformation that affected the Stensgar Mountain quadrangle also affected the rest of northeastern Washington and southeastern British Columbia; it may have been the result of oblique convergence during Mesozoic subduction.
The classical Appalachian, Caledonian, Hercynian, and Mauritanide orogens are now only segments of a once-continuous Paleozoic mountain belt which has been fragmented during Mesozoic-Cenozoic formation of the North Atlantic Ocean. These segments are major parts of the countries surrounding the North Atlantic - most of which are members of NATO. The aim of this NATO conference was to evaluate these fragments in terms of their pre-Mesozoic positions, and to attempt a synthesis of their geologic evolution on an international and orogen-wide scale. Geologists who have studied these scattered remnants have been separated by both geography and discipline. Orogen-wide syntheses have beeen attempted in the past by individuals who are specialists not only in discipline but also in geography; therefore, these attempts have not been satisfactory to everyone. This conference brought together the foremost specialists in different disciplines from each country. They attempted to teach other specialists, not only in their own fields, but in other disciplines, about regional variations and particular problems. The resulting international cross-fertilization, both within and between speciaLties, enriched individual workers and helped to provide a multi-disciplinary overview of the orogen.
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