U-Pb geochronology of Riphean sandstone and gabbro from southeast Siberia and its bearing on the Laurentia-Siberia connection

Thirty-one detrital zircons from the mid-late Riphean Mayamkan Formation sa ndstone (Uy Group) of the Sette-Daban fold belt, southeast Siberia yielded (SHRIMPPb)-Pb-207/Pb-206 ages ranging between 1500-1050 Ma. Other grains yi elded ages between 2.7-1.8 Ga. There is no known source region for the Meso proterozoic zircons in Siberia; however, this range of ages closely matches those of detrital zircons from Neoproterozoic sandstones from northwest Ca nada, 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 s outheast Siberia and northwest Laurentia prior to their separation in the N eoproterozoic. However, two gabbro sills which intrude the Riphean sediment ary 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 M a 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 existi ng data by proposing an alternative continental configuration based on form er continuity of the following tectonic entities: Archean Tungus Province ( Siberia) with Archean Slave Province (Laurentia); Paleoproterozoic Angara f old belt (Siberia) with Paleoproterozoic Wopmay orogen and Great Bear magma tic zone (Laurentia); and Paleoproterozoic Akitkan fold belt (Siberia) with Paleoproterozoic Thelon-Taltson magmatic zone (Laurentia), Our reconstruct ion also considers the proposed northern extension of the Grenville orogen to be a potential source for Mesoproterozoic detrital zircons from the Maya mkan Formation. Such an orientation also is required to explain the apparen t absence of Franklin and/or Mackenzie mafic magmatic rocks and the lack of distinctive Neoproterozoic lithofacies in the Sette-Daban fold belt. An ad ditional conclusion of our study is that the lowermost Uy Group can be no y ounger than ca. 1010 Ma because it is intruded by a diabase sill dated at 1 005 +/- 4 Ma. Previous work indicated that the Uy Group and underlying Lakh anda Group are of late Riphean age (1000-650 Ma). The youngest detrital zir con from the Mayamkan Formation provides a maximum U-Pb age of 1070 +/- 40 Ma for the upper Uy Group. (C) 1998 Elsevier Science B.V. All rights reserv ed.