Ages of some granitic rocks in the Vosges, the Schwarzwald, and the Massif Central

Rb-Sr and K-Ar age detenninations on biotite and muscovite from crystalline rocks in the Vosges and in the Massif Central in France and in the Schwarzwald in Germany are concordant and fall between about 280 and 330 million years. Measurements on zircons give discordant and ambiguous results. Some of the zircons contain large amounts of common lead, much of it in leachable form. Stratigraphically the rocks fall into two time groups, the older late Visean and the younger late Westphalian or early Stephanien. Recent revisions in the stratigraphy of the Vosges and the Massif Central require a corresponding increase in the time-scale value assigned to the boundary between Early and Late Carboniferous (to about 330 million years).