U-PB GEOCHRONOLOGY OF RIPHEAN SANDSTONE AND GABBRO FROM SOUTHEAST SIBERIA AND ITS BEARING ON THE LAURENTIA-SIBERIA CONNECTION

Abstract

Thirty-one detrital zircons from the mid–late Riphean Mayamkan Formation sandstone (Uy Group) of the Sette–Daban fold belt, southeast Siberia yielded SHRIMP 207Pb/206Pb ages ranging between 1500 and 1050 Ma. Other grains yielded ages between 2.7 and 1.8 Ga. There is no known source region for the Mesoproterozoic zircons in Siberia; however, this range of ages closely matches those of detrital zircons from Neoproterozoic sandstones from northwest Canada, which are considered to have been derived from the Grenville Province of southeast Laurentia (all directions cited are with reference to present-day coordinates). These data suggest a formerly close connection between southeast Siberia and northwest Laurentia prior to their separation in the Neoproterozoic. However, two gabbro sills which intrude the Riphean sedimentary succession of the Sette–Daban fold belt are dated here at 1005±4 Ma and 974±7 Ma (U–Pb baddeleyite), an unknown age in northern Laurentia and unlike the widespread and well characterized 723 Ma Franklin and 1267 Ma Mackenzie mafic magmatic events. These somewhat incongruous results cast uncertainty on existing continental reconstructions, which link Siberia to Laurentia from about 1900 to 700 Ma. Our data can be reconciled with existing data by proposing an alternative continental configuration based on former continuity of the following tectonic entities: Archean Tungus Province (Siberia) with Archean Slave Province (Laurentia); Paleoproterozoic Angara fold belt (Siberia) with Paleoproterozoic Wopmay orogen and Great Bear magmatic zone (Laurentia); and Paleoproterozoic Akitkan fold belt (Siberia) with Paleoproterozoic Thelon–Taltson magmatic zone (Laurentia). Our reconstruction also considers the proposed northern extension of the Grenville orogen to be a potential source for Mesoproterozoic detrital zircons from the Mayamkan Formation. Such an orientation also is required to explain the apparent absence of Franklin and/or Mackenzie mafic magmatic rocks and the lack of distinctive Neoproterozoic lithofacies in the Sette–Daban fold belt. An additional conclusion of our study is that the lowermost Uy Group can be no younger than ca. 1010 Ma because it is intruded by a diabase sill dated at 1005±4 Ma. Previous work indicated that the Uy Group and underlying Lakhanda Group are of late Riphean age (1000–650 Ma). The youngest detrital zircon from the Mayamkan Formation provides a maximum U–Pb age of 1070±40 Ma for the upper Uy Group.