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) superimposition of three distinct crustal units has been attributed to Middle to Late Carboniferous thrusting. A kinematic analysis of microstructures within each unit suggests that extension, following the formation of a stack of nappes, is actually responsible for the bulk structure of this region. In order to estimate the related exhumation, the temperature and pressure evolution of the lowermost unit is investigated. It is characterized by (i) a prograde evolution within the stability field of kyanite, followed by (ii) a syn-kinematic, 3-4 kbar, near-isothermal decompression before (iii) cooling. Thermal modeling shows that the isothermal decompression may be related to rapid exhumation (>1mm.a-1), which cannot be accounted for by erosion alone. Therefore, exhumation is best explained by extensional processes, possibly related to gravitational collapse of a thickened crust.

ACKNOWLEDGMENTS

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

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