Two Neoarchean supercontinents? Evidence from the Paleoproterozoic

Abstract

An unresolved question in Precambrian geology is the relationship between Archean crustal fragments that are now separated by younger orogens: were they once contiguous? Williams et al. (1991)proposed the name `Kenorland' for a speculative Neoarchean supercontinent comprising the Archean provinces in North America. Recently, a large number of ca. 2.5–2.0 Ga magmatic, metamorphic, detrital and xenocrystic ages have been reported from North America. We interpret that the wide geographic distribution and temporal spread of these ages may signify long-lived, regional-scale mantle upwelling, and anorogenic magmatic and metamorphic processes related to the protracted breakup of Kenorland. Breakup may have extended from ca. 2.5 to 2.1 Ga, culminating with dispersion of continental fragments at ca. 2.1–2.0 Ga. In North America, ca. 2.5–2.1 Ga intracratonic basin successions (e.g. Hurwitz Group) formed in the interior of Kenorland before dispersion, and passive margin sequences flanking the Superior Province (e.g. Huronian Supergroup) and the Wyoming Province (e.g. Snowy Pass Supergroup) defined the edges of Kenorland. Earliest Paleoproterozoic magmatic and sedimentary rocks, which include voluminous quartz arenites and glacigenic deposits, are consistent with a high-standing supercontinent and a mantle superplume. The Paleoproterozoic record from the Baltic and Siberian shields is similar to that of North America, suggesting inclusion in Kenorland. A slightly different record from the southern continents suggests a second, coexisting supercontinent that included the Zimbabwe, Kaapvaal, and Pilbara cratons, (`Zimvaalbara' of I.G. Stanistreet), the São Francisco Craton, and possibly, cratonic blocks in India. Attenuation of this second supercontinent started earlier than in Kenorland (ca. 2.65 Ga) and was accompanied by high sea level and deposition of vast Lake Superior-type iron formations. Immediately thereafter, both supercontinents became emergent and were subject to global cooling and glaciation.