Earth-Science Reviews 44 1998 95–145
Extending a thickened crustal bulge: toward a new geodynamic
evolution model of the paleozoic NW Bohemian Massif, German
Continental Deep Drilling site SE Germany
Institut fur Mineralogie, Zentrallaboratorium fur Geochronologie der Wilhelms-UniÕersitat Munster, Corrensstr. 24, D-48149 Munster,
Received 28 August 1997; accepted 3 July 1998
Fault-bounded tectonic metamorphic complexes assembling the NW Bohemian Massif around the German Continental
Deep Drilling KTB site are seen to be extremely heterogeneous in tectonic and metamorphic histories. In current models,
the different complexes were supposed to reflect a puzzle of small pre-Devonian microplates, and the related collision events
supposedly lasted until the Carboniferous. Opposed to these models, it will be shown that all the boundaries among the
complexes were formed by detachment, late in a prolonged overall geodynamic history of a thickened crustal bulge, during
extensional tectonics and associated thermal events that outlasted the onset of collision in the SilurianrLower Devonian by
about 70–80 Ma. Micro- structures, petrological and geochronological data of individual complexes predominantly preserve
the late stages rather than the unbroken record of their tectonometamorphic histories. Such partial histories strongly different
among individual complexes, depict diverse snapshots taken at different places in the evolving thickened crustal bulge and at
different instants in its overall evolution, and do not define different precollisional microplates. Predominantly P–T and
deformation episodes after terrane juxtaposition are preserved. This article presents an integrated view of the structural
geology, microscopic fabrics, P–T data and geochronology of such diverse metamorphic complexes. This integrated view
provides a new understanding of 1 the tectonic evolution during Upper SilurianrDevonian collision of the Gondwana-de-
rived Central European lithosphere with Laurussia, 2 the postaccretionary events that lasted through the Upper Carbonifer-
Ž. Ž .
ous and 3 , the earlier Lower Ordovician metamorphic and magmatic history, which is only locally recorded.
Metamorphic complexes occupying the structurally highest position upper tectonic complexes record Devonian and earlier
tectonometamorphic and magmatic events. After the Mid-Devonian, such complexes did not experience any metamorphism.
The recorded Devonian events consist of subduction and exhumation of HP-rocks and their exhumation involved thrusting
and extensional tectonics. Upper tectonic complexes comprise fragments of both the plate that was subducted in this period
and the overriding plate. In the footwall, Carboniferous extension has brought upper tectonic complexes against metamor-
phic complexes that essentially record Lower and Upper Carboniferous tectonometamorphic and magmatic events lower
tectonic complexes . In the lower tectonic complexes, such events are 1 consecutive extensional stages that created at least
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