Geochronology of the Volgo-Uralia Shield
with Svetlana Bogdanova, Elena Bibikova and Alexander Postnikov
New U-Pb SHRIMP geochronology on core samples of the Volgo-Uralia basement, indicate Archaean basement, reworked and affected by various thermal episodes and granulite facies metamorphism. The nature of the Volgo-Uralian Shield, which forms part of Baltica, has long remained enigmatic due to the fact none of it is exposed. Indirect seismic and geophyisical data, as well as numerous deep boreholes facilitated by the wide economic interests in the region (oil and gas) provide the only insights in this cryptic terrain.
Preliminary data suggest the Archaean terane (3.1-2.7 Ga) has been affected by thermal events at 2.6, 2.2 and between 1.9 and 1.8 Ga, giving rise to overprinting granulite facies metamorphism. successive zircon growth, and retrograde shear zones and doming, all affecting the U-Pb isotopic record in these rocks. This renders traditional U-Pb zircon dating techniques susceptible to ambiguous interpretation, leaving careful microprobe U-Pb geochronology the only relaible method to unravel the tectonothermal history of the region.
Results of the geochronological studies will be presented at the "Supercontinents and Earth Evolution Symposium" in Fremantle later this year (26-30 September 2005)