ABSTRACT A diverse range of plutonic to hypabyssal intrusions related to the 1.1 Ga Mid-continent Rift occurs in northeastern Minnesota. These intrusions are grouped into two complexes based on their structural occurrence within the North Shore Volcanic Group (NSVG, a comagmatic volcanic edifice) and their range of emplacement ages. The better known Duluth Complex is composed of gabbroic, anorthositic, and granitic intrusions that were emplaced into the base of the NSVG between 1108 and 1098 Ma. The Beaver Bay Complex is composed of a comparable range of intrusions that were emplaced into more medial sections of the NSVG between 1098 and 1095Ma. This field trip will profile the igneous stratigraphies of two of the best-studied mafic layered intrusions associated with the Midcontinent Rift. The Sonju Lake intrusion is a 1-km-thick lake intrusion associated with the Beaver Bay Complex that shows a classic Skaergaard-type cumulate stratigraphy indicative of closed-system fractional crystallization of a tholeiitic magma. The Layered Series at Duluth (DLS) is a well-differentiated, 4-km-thick sheet-like intrusion that is the type-intrusion of the Duluth Complex. Phase and cryptic layering through the DLS indicates that it evolved as a more open system due to periodic recharge and venting.

ABSTRACT The deglaciation history of northeastern Minnesota and northwestern Ontario is outlined using geological and ichthyofaunal evidence from the continental to local scales. Both published and new data indicate the existence of eastern outlets drawing from pre-and-early Agassiz lakes. Part of the Arctic watershed was impounded between the Duluth Complex highlands and the retreating Rainy lobe. These outlets had their flows routed through the “Keating Complex” and the “Gunflint Arrow Lakes Corridor.” Discharges around the Duluth Complex’s northeast limb reached the Superior basin along Superior lobe ice, then exited down existing pre-glacial river valleys and a prominent, “valley-type” topographic bench between Hovland and Grand Marais, Minnesota.