OLD AND DEER: A STUDY OF PERIDOTITES IN MICHIGAN’S UPPER PENINSULA

The Deer Lake Peridotite and the Presque Isle Black Rocks are two ultramafic formations of Neoarchean age within the Ishpeming Greenstone Belt of Michigan’s Upper Peninsula, and are found only fifteen miles apart. The Deer Lake Peridotite was deformed in processes indicative of the broader, regional-scale tectonics of the region, but little study has been done on the mineralogy and extent and style of alteration. This research aims to better classify the mineralogy of the formation, with particular focus on textural variations observed in thin section, as well as chemical analysis of samples taken from the formation. In addition, this research seeks to correlate the Deer Lake Peridotite’s history of alteration, which may have included alteration by Proterozoic events, with that of the Presque Isle Black Rocks, a formation which has had more extensive study done on its tectonic history and alteration. The comparison between alteration styles in the two formations will help draw conclusions about the tectonic history of Michigan’s Upper Peninsula.