|
Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany Patrick.Obrein{at}uni-bayreuth.de
The evolution of the crystalline internal zone of the European Variscides (i.e. Moldanubian and Saxo-Thuringian) is best understood within a framework of two distinct subduction stages. An early, pre-Late Devonian (older than 380 Ma), subduction stage is recorded in medium-temperature eclogites and blueschists derived from low-pressure basaltic and gabbroic protoliths now found as minor relics in amphibolite facies meta-ophiolite or gneiss-metabasite nappe complexes. A second subduction and exhumation event produced further nappe complexes containing different types of mantle peridotites, along with their enclosed pyroxenites and high-temperature eclogites, associated with large volumes of high-T-high-P (900–1000°C, 15–20 kbar) felsic granulites. Abundant geochronological evidence points to a Carboniferous age (c. 340 Ma) for the high-P-high-T metamorphism as well as an extremely rapid exhumation because the fault-bounded, granulite-peridotite-bearing tectonic units are also cut by late Variscan granitic plutons (315–325 Ma). The massive heat energy for the characteristic, and most widespread feature of the Variscan event, the low-P-high-T metamorphism (750–800°C, 4–6 kbar) and voluminous granitoid magmatism (325–305 Ma), comes from three sources. An internal heat component comes from imbrication of crust with upper-crustal radiogenic heat production potential in the region parallel to the subduction zone; an external mantle heat component is undoubtedly contributing to the transformation of crust taken to mantle depths (i.e. the granulites); and a heat component advected to the middle and lower crust seems inescapable if the hot granulite-peridotite complexes were exhumed and cooled as rapidly as petrological and geochronological evidence seems to suggest. Major mantle delamination and asthenospheric upwelling as a cause of heating in Early Carboniferous times is not supported by geochemical, geophysical or petrological-geochronological studies, although slab break-off probably did occur.
This article has been cited by other articles:
 |
|
 |
|
  P. JEraBek, W.S. FARYAD, K. SCHULMANN, O. LEXA, and L. TAJcMANOVa Alpine burial and heterogeneous exhumation of Variscan crust in the West Carpathians: insight from thermodynamic and argon diffusion modelling Journal of the Geological Society, 2008; 165: 479 - 498. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. A. Ziegler, M. E. Schumacher, P. Dezes, J.-D. Van Wees, and S. Cloetingh Post-Variscan evolution of the lithosphere in the area of the European Cenozoic Rift System Geological Society, London, Memoirs, 2006; 32: 97 - 112. [Abstract] [PDF]
|
|
|
|
|
|
W. Franke The Variscan orogen in Central Europe: construction and collapse Geological Society, London, Memoirs, 2006; 32: 333 - 343. [Abstract] [PDF]
|
|
|
|
 |
|
 M. J. Timmerman Timing, geodynamic setting and character of Permo-Carboniferous magmatism in the foreland of the Variscan Orogen, NW Europe Geological Society, London, Special Publications, 2004; 223: 41 - 74. [Abstract] [PDF]
|
|
|
|
|
|
D. Praeg Diachronous Variscan late-orogenic collapse as a response to multiple detachments: a view from the internides in France to the foreland in the Irish Sea Geological Society, London, Special Publications, 2004; 223: 89 - 138. [Abstract] [PDF]
|
|
|
|
|
|
P. A. Ziegler, M. E. Schumacher, P. Dezes, J.-D. Van Wees, and S. Cloetingh Post-Variscan evolution of the lithosphere in the Rhine Graben area: constraints from subsidence modelling Geological Society, London, Special Publications, 2004; 223: 289 - 317. [Abstract] [PDF]
|
|
