A TECTONIC FRAMEWORK FOR MESOPROTEROZOIC NORTH AMERICA AND SUGGESTED FUTURE RESEARCH DIRECTIONS (Invited Presentation)

The Mesoproterozoic was a time of continental growth, modification, and stabilization in North America. A continent-scale understanding of the tectonic mechanisms that produced these changes is emerging from recent investigations. We now recognize tectonic patterns thanks to increasingly rich datasets. We also see apparent inconsistencies across datasets, which suggest that the research community is on the cusp of constructing a more detailed tectonic framework for the development of the continent.

The emerging tectonic framework for Mesoproterozoic North America shows that igneous rocks were emplaced along and inboard of an active convergent margin that stretched from at least the southwestern US to eastern Canada (present coordinates). This complex orogenic system featured arcs, back arcs, and active sedimentary systems. The orogen (or orogens) also facilitated the addition of new tectonic provinces to the continent and modification of preexisting continental crust.

Inconsistencies between datasets challenge these new tectonic models and point to fruitful directions for future research. We review several apparent discrepancies in the literature that will lead to the development of more complete tectonic frameworks. One, geochemical data show that Mesoproterozoic igneous rocks commonly formed by partial melting of preexisting lower crust, which suggests an upper mantle heat source. At the same time, evidence of subduction modification of the mantle exists regionally in the southwest US. Two, geophysical studies of the midcontinent reveal Mesoproterozoic-aged regional-scale structures that may fit a number of tectonic contexts. Interpreted structures include calderas, distributed magmatic systems, rift basins, depositional basins, and transtensional shear zones. Three, amphibolite- to granulite-facies metamorphism is documented regionally, but the source of heat for high temperature metamorphism and the timing relationship between regional metamorphism and pluton emplacement remain elusive.

Future research should focus on resolving these discrepancies. A tectonic model that can account for detailed regional features within the context of a continent-scale orogenic system will mirror the level of detail we see in modern plate margin systems.