Palaeomagnetism and geochronology of mafic dykes in Siberia

With Sergei Pisarevsky, Michael Wingate, Dimitri Gladkochub, Tatiana Donskaya and others

The primary aim of this project is to elucidate the position of the Siberian craton within the Rodinia supercontinent, and, in particular, its possible connections with Laurentia. The project includes new palaeomagnetic and geochronological studies of Meso- and Neoproterozoic igneous and sedimentary rocks in Siberia; a tectonostratigraphic comparison of Meso- and Neoproterozoic sedimentary successions along the margins of Siberia and geological, geochronological, and geophysical
comparison of Archean and Paleoproterozoic blocks, terranes, and orogenic belts in Siberia and Laurentia. The new data will allow compilation of Precambrian tectonic maps for Laurentia and Siberia.

In addition to palaeomagnetic and geochronological samples collected in Siberia by Dr Wingate in 2003, new material was brought to the TSRC in 2004 by our collaborators Drs Pavlov, Gladkochub, and Donskaya. Measurements and interpretation are essentially complete, and articles are in preparation.

We have assessed different Siberia-Laurentia reconstructions using palaeomagnetic, geochronological, geochemical, and geological data (see 2003 TSRC Annual Report). Our new SHRIMP U-Pb ages and geochemical data for mafic dykes and sills in southern Siberia indicate that they share similarities with intrusions of the 723 Ma Franklin large igneous province (LIP) in northern Laurentia. However, the mafic rocks in Siberia are far less extensive than those in northern Laurentia, which may be consistent with an “indirect” connection between Siberia and Laurentia, with additional continental fragments between the two cratons, as suggested by palaeomagnetic and other data. Possible candidates for intervening fragments should contain evidence of the c. 725 Ma LIP, and include North Alaska, North Chukchi Peninsula, and some Arctic islands. A paper summarizing this study has been submitted to Precambrian Research.

Our new SHRIMP U-Pb zircon and baddeleyite results for mafic sills, dykes, and volcanic rocks in the Olenek uplift of far northern Siberia show them, and the sedimentary rocks they intruded, to be Paleoproterozoic rather than Neoproterozoic, as was thought previously. This result requires a substantial revision of Siberian stratigraphy. Palaeomagnetic data show that these mafic rocks are coeval; some additional SHRIMP geochronology in 2005 will constrain their preliminary age of ~1860 Ma more precisely. A positive baked-contact test indicates that original magnetisations in the mafic rocks have been preserved.