GEOCHRONOLOGY OF THE MID-GERMAN CRYSTALLINE RISE WEST OF THE RIVER RHINE

The mid-German crystalline rise has its westernmost exposures at the w estern margin of the Rhine graben in the southern Pfalz and the northe rn Alsace. The outcrops are made up of granitoid rocks and minor volca no-sedimentary sequences. Radiometric ages obtained by U/Pb, Pb/Pb, Sm /Nd and Rb/Sr analyses of the igneous rocks from this area range from similar to 433 to similar to 325 Ma thus covering a time span from the Silurian to the end of the lower Carboniferous. Because the investiga ted rocks are - according to their chemical composition - largely rela ted to subduction zone environments, the following three geodynamical scenarios are postulated, always taking subduction of oceanic crust be neath the mid-German crystalline rise into account: (a) subduction of the Rheic ocean during the Silurian from the north; (b) subduction of the Rhenohercynian ocean during the late Devonian (similar to 369 Ma) from the north; (c) subduction of the Saxothuringian ocean during the lower Carboniferous (similar to 334 Ma) from the south.