2.5-2.4 GA GLOBAL MAGMATISM: REMNANTS OF SUPERCONTINENTS OR PRODUCTS OF SUPERPLUMES?

A multitude of changes ushered in Paleoproterozoic Earth and hint at the possibility that a fundamental transformation occurred in the entire Earth system at this time. The distinctive 2.5-2.4 Ga period in Earth history marks one of the most extensive and perhaps voluminous periods of Proterozoic mafic and ultramafic magmatism, the onset of a significantly oxygenated atmosphere (‘Great Oxidation Event’), the most prolific production of banded iron formations in Earth history, the possible first occurrence of ‘Snowball Earth’ conditions, rapid changes in the composition of seawater, a dramatic increase in the paleointensity of Earth’s magnetic field and the global coincidence of mafic magmatism and high grade (granulite facies) metamorphism. Evidence for predominantly 2.5-2.4 Ga mafic and ultramafic magmatism together with subordinate granitic magmatism exists for most Archean cratons worldwide: North America (Superior, Wyoming, Churchill), Scotland (Lewisian), Eastern Europe (Karelia), Australia (Gawler, Yilgarn, Pilbara), Antarctica (Napier), India (Dharwar), and China (North China). The extent to which this global magmatism could reflect focused mantle plume activity impacting one or a small number of supercontinents or could reflect heightened mantle plume activity both in terms of their numbers and magnitude is pivotal for understanding whether global mafic magmatic events can be used as a robust correlation pin in constraining Precambrian supercontinent reconstructions. A compilation of more than 50 robust U-Pb baddeleyite/zircon ages for 2.5-2.4 Ga magmatism reveals that as many as five discrete ‘events’ can be recognized; 1) 2510-2500 Ma (Mistassini, Kaminak I, Kola, Ptarmigan), 2) 2480-2470 Ma (Matachewan Igneous Events, Mount Hardy), 3) 2450-2440 Ma (Hearst, Karelia layered mafic intrusions, Kaminak II, Blackfellow Hills), 4) 2420-2410 Ma (Widgiemooltha, Scourie I, Du Chef), and 5) 2380-2370 Ma (Scourie II, Bangalore). Although there may be some potential for using certain 2.5-2.4 Ga mafic magmatic events for constraining continental reconstructions (e.g. Superior-Karelia), the present data set indicates that the beginning of the Proterozoic marks the onset of prolific mantle plume activity that lasted for approximately 120 m.y.