Far from boring: A new Grenvillian perspective on Mesoproterozoic tectonics

Abstract

The “boring billion” (1.8 to 0.8 billion years ago) is an enigmatic period of Earth's evolution viewed by some as a time of tectonic quiescence reflecting secular changes in our planet's convection regime, either from sluggish global plate tectonics regime or from a wholly different regime. The confusion about this time-span stems from diverging interpretations of an ambiguous geological record, which points to a Mesoproterozoic world dominated by volcanic arcs, but also includes the formation of the massive Grenville Orogen. Here we present a compilation of multidisciplinary geological datasets, that are incompatible with the current tectonic paradigm, whereby the Grenville Orogen developed as an Andean-like arc at the margin of the Laurentia continent (now North America) and was reworked during a collision with the Amazonia continent (now South America). We argue, instead, that the geological record and proxies, with emphasis on those from the main exposure of the Grenville Orogen in the Grenville Province of eastern Canada, are consistent with the assembly of a distinct continent, which we coin Shawiniga (1.2-1.15 Ga), through the amalgamation of mature oceanic arcs/back-arcs offshore of Laurentia followed by a Shawiniga-Laurentia collision (∼1.03 Ga). This new model reveals that the transition from the supercontinent Columbia to Rodinia involved long-lived passive margins and subduction zones, as well as continental assembly through arc collisions, resolving the longstanding contradiction between tectonic proxies and the geological record and confirming the Mesoproterozoic was actually an exciting Era.