MAGMATIC PULSES DURING THE PALEOPROTEROZOIC ASSEMBLY OF SARMATIA AND VOLGO-URALIA: ~2066 AND 2075-2085 MA MANTLE PLUME EVENTS

Baltica consists of three cratons: Fennoscandia, Sarmatia, and Volgo-Uralia. The Voronezh Crystalline Massif (VCM) of Russia straddles the suture between the latter two cratons; subduction was to the west under Sarmatia and culminated with the collision at 2.1-2.03 Ga based on ages of synorogenic granitoids (Bibikova et al., 2009). The VCM, largely covered by Phanerozoic sediments, consists of two megablocks, Kursk of Sarmatia and Khoper of Volgo-Uralia separated by the Losev Mobile Belt (LMB), that are highly endowed with Ni-Cu bearing mafic to ultramafic intrusions. The intrusions based on imprecise dates obtained before our study could have been correlative with the economically important Bushveld Igneous Complex (BIC) in South Africa. The BIC was emplaced at ~2059-2054 Ma. New, high-precision U-Pb ages on baddeleyite and titanite define two magmatic pulses on the VCM, ~2066 Ma and 2075-2085 Ma, which are different in age from the BIC and overlap in time with the assembly of Sarmatia and Volgo-Uralia. Intrusions of the 2075-2085 Ma event are common on Khoper, but are also found in Kursk, whereas the ~2066 Ma event affected both Kursk and the LMB. Although there is an apparent shift in the locus of magmatism to the west with the younger age, importantly both megablocks were affected by these events indicating their proximity. The 2075-2085 Ma event overlaps in age with the Pavlovsk synorogenic granitoid complex (Bibikova et al., 2009). Similar-age orogenic events are recognized in West and Southern Africa and South America (Ubendian, Birimian, Magondi, Limpopo, and Transamazonian), while in North America and Fennoscandia new continental margins were formed. These tectonomagmatic events coincide in age with the end of the Lomagundi carbon isotope excursion in seawater composition and deoxygenation of the atmosphere-ocean system. Our study provide additional support to the recurrent association between assembly of continents and LIPs, when ocean closure could have led to formation of a lithospheric lid that caused regional mantle heat perturbation and LIP generation. Furthermore, changes in surface redox conditions and biogeochemical carbon cycle at that time could have been triggered or influenced by these tectonomagmatic processes, underlining the link between evolution of the interior and surface conditions.