The Variscan French Massif Central - a new addition to the ultrahigh pressure metamorphic 'club': exhumation processes and geodynamic consequences

This paper presents the first documentation of coesite-bearing eclogites in the eastern French Massif Central (Monts du Lyonnais unit) and discusses t he exhumation processes for these very high-pressure rocks. A combination o f mineralogical and geochronological datasets allows us to quantify a depth -time path and related exhumation rates. High-pressure metamorphism is cons trained to 400-420 Ma (minimum 28 kbar or ca. 90 km). By 360-380 Ma, the ro cks were exhumed to 30 km depth. These kinetic results conform to the geolo gical constraints extracted from the tectonic and sedimentary record of the eastern French Massif Central. These multidisciplinary approaches provide new information on Paleozoic oro geny and allow us to discuss the relative roles of subduction and collision in exhumation of very high-pressure rocks. We suggest that a significant a mount of exhumation of these rocks occurred during subduction, prior to con tinental collision; continental collision itself was responsible only for t he final stages of exhumation under a transpressive regime. (C) 2001 Elsevi er Science B.V. All rights reserved.