CARBONIFEROUS EXTENSION IN THE VARISCAN BELT :STRUCTURAL AND PETROLOGICAL EVIDENCES FROM THE VOSGES MASSIF (EASTERN FRANCE)

P.F. Rey*, J.P. Burg** and J.M. Caron*

*Laboratoire des Sciences de la Terre, ENS Lyon, 69364 LYON Cedex 07,France

**Centre Geologique et Geophysique, USTL, 34095 Montpellier Cedex 05,France

in: GEODINAMICA ACTA (1992), Vol.5, 1-2, PP.17-36.

ABSTRACT

In the Moldanubian domain of the Vosges massif (NE France) superimpositionof three distinct crustal units has been attributed to Middle to Late Carboniferousthrusting. A kinematic analysis of microstructures within each unit suggeststhat extension, following the formation of a stack of nappes, is actuallyresponsible for the bulk structure of this region. In order to estimatethe related exhumation, the temperature and pressure evolution of the lowermostunit is investigated. It is characterized by (i) a prograde evolution withinthe stability field of kyanite, followed by (ii) a syn-kinematic, 3-4 kbar,near-isothermal decompression before (iii) cooling. Thermal modeling showsthat the isothermal decompression may be related to rapid exhumation (>1mm.a-1),which cannot be accounted for by erosion alone. Therefore, exhumation isbest explained by extensional processes, possibly related to gravitationalcollapse of a thickened crust.

ACKNOWLEDGMENTS

We wish to express our appreciation to L.Mercier, L.Latouche and J.C. Goujoufor stimulating and constructive discussions. H. Echtler and Ch. Teyssierprovided very helpful reviews. Special thanks are due to M. Guiraud forhaving critically reviewed the manuscript and allowed strong improvementsof the petrological analysis. This study was financed by the INSU-CNRS(ATP-ECORS 891705).

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