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Pressure-temperature-time-deformation paths in metamorphic rocks and tectonic processes, as exemplified by the Variscan orogeny in South Brittany, France.

Abstract : To relate metamorphic conditions to tectonic processes, three main complementary steps may be followed. First, extract information from mineral assemblages which occur in metamor­ phic rocks in order to construct quantitative P—T—t paths. Second, correlate successive metamorphic fabrics with progressive evolution of P and T through time, and construct P—T— t—deformation paths in order to understand thermal/deformation histories. Third, model the thermal evolution of orogenic belts, par­ ticularly the case of continental collisions. Fol­ lowing these steps, and in the light of recent thermal models, this paper discusses large-scale structural/microstructural (Audren 1987) and geothermobarometric data (Triboulet & Audren 1985a, 1988) obtained on highgrade metamor­ phic rocks from the River Vilaine area in South Brittany. Geological setting and tectonic/metamorphic evolution The River Vilaine area in South Brittany (France) is part of the western axial zone of the European Hercynian belt (Fig. la). The meta­ morphic rocks consist of a volcano-detrital se­ quence of interbedded mica-schists (abundant) and amphibolites (scarce) and are interpreted as having formed on an active continental mar­ gin (oceanic/continental sedimentary associ­ ation) (Triboulet & Audren 1985b). During Palaeozoic times these rocks underwent a com­ plex tectonic and metamorphic two-stage evol­ ution, corresponding to successive Devonian and Carboniferous orogenic events that have been clearly separated through time and space (Audren 1987).
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Claude Audren, Claude Triboulet. Pressure-temperature-time-deformation paths in metamorphic rocks and tectonic processes, as exemplified by the Variscan orogeny in South Brittany, France.. J. S. Daly, ; R. A. Cliff; B. W. D. Yardley,. Evolution of Metamorphic Belts, 43, Geological Society of London, pp.441-446, 1989, Geological Society of London, Special Publication, ⟨10.1144/GSL.SP.1989.043.01.39⟩. ⟨insu-01507126⟩

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