The Not-So-Boring Billion: A metallogenic conundrum during the evolution from Columbia to Rodinia supercontinents

Abstract

Following the commencement of assembly of Columbia at ca. 2.0 to 1.8 Ga with its normal convergent margin metallogeny rich in orogenic gold and VMS Cu-Zn-Pb systems, the Earth entered the Boring Billion phase from 1800 to 800Ma from Late Paleoproterozoic to the dawn of the Neoproterozoic, a transitional period prior to the assembly and breakup of Rodinia. The Boring Billion is considered as a static period in terms of the evolution of global tectonics, the atmosphere, oceans, and life itself. Unlike the history of previous supercontinents, there is limited evidence of extensive breakup and continental drift during the transition from breakup of Columbia to the assembly of Rodinia. The low strain accordion-style tectonic regime appears to have been typified by intermittent periods of variable degrees of extension, rifting, and asthenosphere upwelling followed by compression and closure of extensional basins.The anomalous accordion-type tectonics resulted in the formation and preservation of an equally anomalous but richly endowed metallogeny. Varying degrees of rifting, asthenospheric upwelling, intermittent magmatism derived both from mantle melting, and induced hydrothermal circulation resulted in a variety of giant mineral deposits that were preserved on the margins of buoyant lithosphere during mild compression. In accordance with their inferred relationship to accordion tectonics, the metallogeny was episodic with peaks at ca. 1.7–1.6, 1.4, and 1,1 Ga. The world's largest IOCG, carbonatite REE, lamproite diamond, unconformity U, SEDEX, and BHT deposits represent a metallogenetic bonanza during this period. The more intensively metal endowed blocks within Columbia were smaller blocks with largely Paleoproterozoic lithosphere, particularly Central Australia, and the North American Craton with its myriad of internal blocks. These appear to have been most susceptible to rifting under relatively low strain accordion-style tectonism due to their high density of lithosphere margins relative to their surface area. Overall, it appears that it was the relative lack of tectonic activity and continental drift in the Boring Billion that was responsible for the not-so-boring but, rather spectacular and unique, metallogeny of that period of Earth's history.