NEW PALEOMAGNETIC AND ISOTOPIC DATA FROM MESOPROTEROZOIC BASIC SILLS AND DYKES OF THE ANABAR UPLIFT (NORTHERN SIBERIA) AND THEIR IMPLICATION FOR THE SIBERIA-LAURENTIA CONNECTION

During several last years we conducted paleomagnetic investigations of dykes and sills located in the western and northern parts of the Anabar Uplift and exposed along the valleys of Dzhogdzho, Kotuykan and Fomich rivers. As part of this work we undertook the isotopic investigations aimed to determine the age of studied magmatic bodies. In spite of high quality result (SHRIMP, ca 1760 Ma) obtained from zircons from Dzhogdzho river sill (western Anabar) we cannot presently use it for estimation of time of the sill emplacement as there are some reasons to consider the zircons as inherited (Khudoley et al, 2007). However Sm-Nd isochrone age (1513+-51 Ma) obtained from a sill of Fomich river valley (northern Anabar) seems to indicate the age of the sill indeed.

Northern and western sills and dykes yield close but statistically distinct paleomagnetic poles located in peri-equatorial area of the central Pacific. Positive baked contact test, presence of two polarity directions and consistency of directions isolated from distant magmatic bodies within the study areas support the primary origin of remanence.

The proximity of paleomagnetic poles obtained from North and West of the Anabar Uplift suggests that magmatic activity in these areas (as well as in south anabarian Kounamka region – Ernst et al, 2000) took place in close but not exactly the same time ca 1500 Ma. If so, then accumulation of all or almost all Anabarian Riphean sequence ceased by 1500 Ma, i.e. much earlier that it was considered before. The paleomagnetic pole located very close to our Anabarian poles has been obtained by Gurevich (1984) and Konstantinov (2005) from basic sills occurring within the Mesoproterozoic section of the Olenek Uplift more than 1000 km distant from the Anabar Uplift. This proximity suggests that Olenek intrusions were formed about in the same time and that importance of 1500 Ma magmatic event oversteps the limits of the Anabarian region.

The comparison of nearly coeval Meso-Neoproterozoic (1500-950 Ma) paleomagnetic poles of Laurentia and Siberia indicates some coordination in general trends of both craton movements and thus can be considered as the argument in favor of Siberia-Laurentia coexistence within large continental landmass, which probably survived a break up of Paleoproterozoic supercontinent and became later the part of Rodinia.