CRUSTAL THICKNESS EVOLUTION OF THE GRENVILLE OROGEN

The Grenville Province on the eastern margin of Laurentia represents a Mesoproterozoic orogenic plateau in the core of the supercontinent Rodinia. As an ancient protracted Himalayan-style orogen, its orogenic history is important to the understanding of global tectonic and environmental evolution in the Mesoproterozoic. High-grade metamorphic terranes and high-temperature magmatism, like A-type granites and massif anorthosites, are widespread in this orogen (Indares 2020, Gondwana Res). The anomalously high occurrences of Nb, Y, and Zr-bearing minerals and corresponding enrichments of Nb, Y, and Zr in igneous rocks suggest that the Grenville orogen was distinctively hot (Liu et al. 2017, Nat Comm), which might be associated with, or result in, a relatively thin crust. The bulk-rock [La/Yb]_N ratios of intermediate-to-felsic rocks record the changes in crustal thickness over the course of the orogeny (Profeta et al. 2015, Sci Rep). In this study, we compiled the geochemical data of plutons from the full geographic extent of the North American Grenville province from Newfoundland to Texas, representing 152 plutons in total. Preliminary results show episodes of crustal thickening during the Shawinigan (1190-1140 Ma), Ottawan (1085-1040 Ma), and Rigolet (1030-975 Ma) stages of the orogeny. The Shawinigan thickened crust (55 ± 6 km) was deconstructed in a rapid thinning event from 1170-1140 Ma, overlapping the emplacement ages of major anorthosite-mangerite-charnockite-granite (AMCG) suites. The thickest crust developed in the Ottawan stage (59 ± 8 km) during the culmination of continental collision and plateau uplift, but the Ottawan crust was still about 10 km thinner than the modern Tibetan Plateau. Finally, the Rigolet stage saw a general thinning trend to ~40 km. The Grenvillian plateau failed to reach the thickness of its modern counterpart due to repeated episodes of lithospheric thinning that might be associated with enhanced asthenosphere-lithosphere interactions in response to a warmer mantle (Dijkstra et al. 2016, EPSL).