The Petrology and Geochemistry of Keweenawan Diabase Dikes in Ontonagon, Gogebic, Iron and Dickinson Counties, Michigan

Author

James J. Hahnenberg, Western Michigan University

Date of Award

8-1981

Degree Name

Master of Science

Department

Geological and Environmental Sciences

First Advisor

Dr. John D. Grace

Second Advisor

Dr. Lloyd J. Schmaltz

Third Advisor

Dr. Ronald B. Chase

Access Setting

Masters Thesis-Open Access

Abstract

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 Fe0_t. 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.

Recommended Citation

Hahnenberg, James J., "The Petrology and Geochemistry of Keweenawan Diabase Dikes in Ontonagon, Gogebic, Iron and Dickinson Counties, Michigan" (1981). Masters Theses. 1834.
https://scholarworks.wmich.edu/masters_theses/1834