EMPLACEMENT OF THE MESOPROTEROZOIC WAUSAU SYENITE COMPLEX, WISCONSIN

The Wausau Syenite Complex (WSC) in Marathon County, Wisconsin is an intrusive complex of granitoids emplaced approximately 1.5 Ga. It is traditionally considered part of a major anorogenic ferroan granite magmatic event that affected the southern margin of Laurentia circa 1.4 Ga. Recent studies have recognized a Laurentian-scale accretionary margin between 1520-1340 Ma, including the Pinware Orogeny in the northeast, the Picuris Orogeny in the southwest, and the most recently attributed section, the Baraboo Orogeny centered in Wisconsin. This new hypothesis provides intriguing opportunities to reconsider the origin and tectonic setting of WSC emplacement as well as other Mesoproterozoic granitoids in Wisconsin, including the larger 1.4 Ga Wolf River Batholith. This research project will use the orientation of magnetic fabrics within the WSC to better understand how the batholith was emplaced. The project will consist of an anisotropy of magnetic susceptibility (AMS) survey and thin section analysis of each granitoid within the WSC. With these data, the magmatic flow directions and any subsequent tectonic overprint can be determined, which can be used to constrain the location of the magmatic feeder and the tectonic environment of emplacement. By focusing on these oldest known Mesoproterozoic ferroan granites in the region, we can learn about the timing and geometry of the earliest Baraboo orogenesis. This study will address the question of how these enigmatic granites fit into the overall tectonic history of the Great Lakes Region.