Deducing the ancestry of terranes: SHRIMP evidence for South America-derived Gondwana fragments in central Europe

We present here an example of how the sensitive high-resolution ion micropr obe (SHRIMP) zircon dating method can provide a terrane-specific geochronol ogical fingerpnint for a rock and thus help to reveal major tectonic bounda ries within orogens, This method, applied to inherited zircons in a ca, 580 Ma metagranitoid rock from the eastern Bohemian Massif, has provided, for the first time in the central European Variscan basement, unequivocal evide nce for Mesoproterozoic and late Paleoproterozoic geologic events ca, 1.2 G a, 1.5 Ga, and 1.65-1.8 Ga. The recognition of such zircon ages has importa nt consequences because it implies that parts of the Precambrian section of Variscan central Europe were originally derived from a Grenvillian cratoni c province, as opposed to the common assumption of an African connection. A comparison with previously published SHRIMP data suggests, however, that t hese Mesoproterozoic and late Paleoproterozoic zircon ages may be restricte d to the Moravo-Silesian unit in the eastern Variscides, whereas the Saxoth uringian and Moldanubian zones appear to contain a typical north African (i .e., Neoproterozoic plus Eburnian) inherited-zircon age spectrum. This find ing supports new tectonic concepts, according to which Variscan Europe is c omposed of a number of completely unrelated terranes with extremely differe nt paleogeographic origins. The Moravo-Silesian unit can be best interprete d as a peri-Gondwana terrane, which was situated in the realm of the Amazon ian cratonic province by the late Precambrian, comparable to the Avalonian terranes of North America and the United Kingdom.