Integrated Paleomagnetism and U-Pb Geochronology of Mafic Dikes of the Eastern Anabar Shield Region,Siberia: Implications for Mesoproterozoic Paleolatitude of Siberia and Comparison with Laurentia

摘要

This article reports the first joint paleomagnetic and U-Pb geochronologic study of Precambrian diabase dikes in the Anabar Shield and adjacent Riphean cover of Siberia. It was undertaken to allow comparison with similar published studies in Laurentia and to test Proterozoic reconstructions of Siberia and Laurentia. An east-trending Kuonamka dike yielded a provisional U-Pb baddeleyite emplacement age of 1503 ::!: 5 Ma and a virtual geomagnetic pole at 16°S, 221°B (dm = 17°, dp = 10°!. A paleomagnetic pole at 6°N, 234°E (dm = 28°, dp = 14°) was obtained from five Kuonamka dikes. An east-southeast-trending Chieress qike yielded a U-Pb baddeleyite emplacement age of 1384::!: 2 Ma and a virtual geomagnetic pole at 4°N, 258°E (dm = 9°, dp = 5°). Kuonamka and Chieress poles are interpreted to be primary but do not average out secular variation. Assuming that the Siberian Plate has remained intact since the Mesopro- terozoic, except for mid-Paleozoic opening of the Viljuy Rift, then the above results indicate that the Siberian Plate was in low latitudes at ca. 1503 and 1384 Ma, broadly similar to low latitudes determined for Laurentia from well- dated paleopoles at 1460-1420, 1320-1290, and 1267 Ma. This would allow Laurentia and Siberia to have been attached in the Mesoproterozoic, as suggested in several recent studies based on geological criteria. However, because paleo- magnetic results from the Anabar Shield region do not average out secular variation and the ages of poles from Siberia and Laurentia are not well matched, it is not yet possible to distinguish between these reconstructions or to rule out other configurations that also maintain the two cratons at low paleolatitudes.