The Precambrian bedrock of northern Wisconsin hosts the 1.8-1.9Ga billion-year-old Penokean Orogeny. The Penokean Orogeny involves the collision of volcanic arcs and smaller continental crustal blocks. These blocks are known as the Pembine-Wausau Terrane and the Marshfield Terrane. The Eau Pleine Shear Zone marks the boundary between these two terranes. Recent studies within the Marshfield Terrane indicate a more complex geological structure than previously understood, the highly variable ages in this area highlight the need to re-evaluate the significance of this structural boundary between the Pembine-Wausau and Marshfield terranes. Clusters of magmatic rocks found near the Eau Pleine Shear Zone could help determine the nature of this crustal boundary. Magmas that are generated before, during, or after the collision inherit the geochemical and isotopic characteristics of the crustal blocks they interact with. For this research project, samples were collected from both intrusive and volcanic rocks that are found on both sides of the Eau Pleine Shear Zone, these samples were then prepared for geochemical and petrographic analysis. The results of this work will allow us to evaluate historical tectonic models of the Lake Superior region and determine whether the Eau Pleine Shear Zone is indeed an appropriate terrane boundary.
