Crystallization of pyroxenes in an iron-rich diabase from Minnesota

Abstract

The Beaver Bay diabase forms an irregular sill-like intrusion about 3000 feet in thickness exposed over a distance of approximately six miles from Split Rock to Beaver Bay on the north shore of Lake Superior, Minnesota. It is intrusive into the Keeweenaw volcanic series above the Duluth gabbro to which it is almost certainly related. It is the largest of many such sills in this region and includes several petrographic facies grading from troctolite, through olivine-gabbro, normal gabbro, and ferrogabbro to red granite.