Geochemistry of North Shore Hypabyssal dikes and sills in the Midcontinent Rift of Minnesota: an example the 47th Avenue sill
This study presents geochemical data for several of the numerous small to large dikes and sills, including the 47th Avenue sill, exposed along the shore of Lake Superior in and north of Duluth, Minnesota. These intrusions are late magmatic features of the Proterozoic Midcontinent Rift System and together form the North Shore Hypabyssal Group. The dikes are geochemically distinct from the sills, and, when the two are exposed together, the younger dike intrudes the older sill. Dikes are primitive with Mg# up to 68, have positive eNd values, and are oriented approximately northsouth with steep westerly or near vertical dips. The older sills are more evolved, usually have eNd values near or below 0, and have the same gentle easterly dip as the thick sequence of North Shore Volcanic Group flows they intrude. Dike compositions correlate best with a mixture of widespread basalt compositions types 4 and 5, with primitive geochemistry and positive eNd values, whereas sill compositions are similar to widespread ba...