Provenance of Late Ordovician clastic sedimentary rocks in Jämtland, central Sweden

Zircon grains extracted from three sedimentary units within the Caledonian Lower Allochthon in Jamtland, central Sweden, were investigated for provenance studies using LA-ICP-MS. 207 Pb/ 206 Pb ages fall into the intervals: 3.1-1.7 Ga (Ronnofors Conglomerate), 3.2-1.4 Ga (Ede Quartzite), and 2.6-1.1 Ga (Kyrkas Quartzite). The age distribution of the Ronnofors and Kyrkas units vary sufficiently to suggest different source areas. The Ede Quartzite constitutes a mixture of the Kyrkas and Ronnofors provenance groups. The zircon age spectrum of the Kyrkas Quartzite reflects the typical age group present in the Jamtland basin in late Ordovician. In comparison, most zircon grains from the Ronnofors Conglomerate were derived from a local source, and only a small portion of these grains is characteristic for the basin. The Ede Quartzite contains a mixture of the typical basinal and, to a lesser extent, locally derived material. The variation in age distribution between the Ede and Kyrkas Quartzites reflects differ- ent dominating source areas. Tectonic activities along a shear zone (a continuation of SEDZ), which runs through the Ede and Kyrkas areas may be responsible for the noted differences in source areas. A deriva- tion from older sedimentary rocks to the present west-southwest and/or the Southwest Scandinavian Domain is suggested for the younger parts (