Abstract

The distribution of allochthonous versus parautochthonous carbonate platforms, combined with the timing of initial continental-rift magmatism versus the timing of subsequent rifting of the continental margin, provides tectonostratigraphic evidence for the formation and isolation of the oldest documented microcontinent, perhaps as a consequence of the impingement of a mantle plume onto a cratonic margin during the Paleoproterozoic. Initial rifting of the Archean nucleus of North America in eastern Canada is constrained to have been diachronous between 2.17 and 2.03 Ga. Renewed rifting of a segment of the continental margin, 292 to 120 m.y. later, was accompanied by the emplacement of ultramafic layered sills, the accumulation of komatiitic and alkalic basalts, the deposition of banded iron formations and the isolation of a microcontinent and its 1.93 Ga continental shelf succession (subsequently accreted to the telescoped continental margin during collisional orogenesis).

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