Timing of granitoid magmatism in the eastern mid-German crystalline rise

The eastern parts of the mid-German crystalline rise (MGCR) are exposed in the Spessart. Ruhla and Kyffhauser crystalline complexes and known from bor eholes in the region of Dessau. In this study we determined igneous formati on ages of granitoid intrusives and orthogneisses from this part of the MGC R using the Pb/Pb single zircon dating technique. The intrusion ages of the granitoids range from similar to 489 to similar to 302 Ma (i.e. from lower Ordovician to upper Carboniferous). The grouping of these ages marks sever al distinct magmatic episodes during the Variscan orogeny. with a major pea k at the end of the lower Carboniferous. We tentatively suggest the followi ng geodynamic scenario for the origin of the granitoid magmas in the variou s parts of the MGCR. 1. In the Ordovician, Gondwana disintegrated. Remnants of this stage are preserved in the central and eastern part of the MGCR. 2 . Tn the Silurian, granitoid magmatism was triggered by subduction undernea th the MGCR from the North. Such magmatic rocks occur in the central part o f the MGCR and to a lesser extent in the western part, but not in the north east. 3. In the upper Devonian. magmatism originated in response to subduct ion of the Rhenohercynian Ocean underneath the MGCR from the North. This is only documented in the western part of the MGCR. 4. At the end of the lowe r Carboniferous, at ca. 330 Ma, subduction from the South generated volumin ous granites in the entire MGCR. 5. In the upper Carboniferous. post-tecton ic granitoids were formed in the central and eastern parts, documenting the end of the Variscan orogenic cycle. (C) 2001 Elsevier Science Ltd. All rig hts reserved.