Date of Award
Master of Science
Geological and Environmental Sciences
Dr. John D. Grace
Dr. Lloyd J. Schmaltz
Dr. Ronald B. Chase
Masters Thesis-Open Access
Petrographic and chemical studies of Keeweenawan-age diabase dikes in Michigan's Upper Peninsula show two major groupings, Porcupine Mountain dikes and Lower Keweenawan dikes consist of two major rock types, fine-grained smaller dikes and the coarse-grained central portions of larger dikes. Major minerals are subophitic plagioclase and pyroxene. The rocks, as compared to the "average" basalts, are low in Al203, high in Ti02, K20, P205 and contain moderate amounts of Fe0t. They are classified as quartz tholeiites. Several parental magma sources that would account for these and other Keweenawn igneous units are presented; the most acceptable is derived from 1-1.5% partial melting of pyrolite at a depth of 50-75 km. The Keweenawn basalts were derived from a tectonic environment similar to a plume-generated oceanic island such as Iceland. The Porcupine Mountain dikes are more alkalic than the Lower Keweenawan dikes and show greater secondary alteration.
Hahnenberg, James J., "The Petrology and Geochemistry of Keweenawan Diabase Dikes in Ontonagon, Gogebic, Iron and Dickinson Counties, Michigan" (1981). Masters Theses. 1834.