Abstract This field trip examines deformed Archean basement, and variably metamorphosed supracrustal rocks and an exhumed midcrustal batholith of late Paleoproterozoic age in east-central Minnesota. Collectively, these rocks reveal an approximately 100 m.y. geologic history of crustal growth and stabilization of this part of the craton. The Penokean orogen in Minnesota consists of a northern foreland basin (the Animikie basin), a medial fold-thrust belt, and a southern high-grade metamorphic and plutonic terrane, representing two major orogenic events: the Penokean (geon 18) and Yavapai (geon 17) orogenies. The 1870–1830 Ma Penokean orogenic rocks are part of a belt of juvenile crust accreted onto the southern margin of Laurentia-Baltic continent during the late Paleoproterozoic. Metamorphism along the southern margin of the Archean Superior province has been historically attributed to the Penokean Orogeny, in a corridor of amphibolite-facies rocks which record 1.86–1.80 Ga (geon 18) metamorphic ages that correspond to the culmination of arc accretion. However, a widespread geon 17 amphibolite-facies metamorphic overprint is also recorded along the regions of greatest thickening of the Penokean crust, which corresponds to the tectonically buried Archean-Proterozoic continental margin. This was also the locus of emplacement of the voluminous east-central Minnesota batholith, composed of some twenty separate intrusions that range from mafic to dominantly felsic-intermediate compositions. Most of these are Yavapai in age, with emplacement ages between 1787 and 1772 Ma.

ABSTRACT This field trip is an overview of Precambrian terranes in northeastern Minnesota using some of the most illustrative and accessible exposures—the term "classic" refers to the fact that many were the basis for earliest geologic study of the Precambrian and continue to be exemplary. The geology is presented in the context of major orogenic, rifting, and meteorite impact events during evolution of the North American continent. The Archean rocks are the products of three periods of orogenesis: the ca. 2695 Ma Shebandowanian orogeny that created major folds and thrust stacks; the ca. 2680 Ma Minnesotan orogeny that produced regional transpressive fabrics, folds, and metamorphism to greenschist-amphibolite grade; and a third event that produced localized faulting and folding of earlier structures and fabrics. The Sheban-dowanian may represent collision of the Wawa subprovince with the composite Superior superterrane to the north. The Minnesotan can be attributed to oblique collision of the Minnesota River Valley subprovince with the Superior superterrane. Structures bounding major components of the Superior Province are locally inferred to be thrust faults that formed during terrane assembly. Their vergence and offset histories are derived from seismic surveys in Minnesota and extrapolation from Lithoprobe and NATMAP transects in adjacent Canada. The Paleoproterozoic rocks are the products of three orogenic and rifting events, reflecting continued continental growth at Geons 18, 17, and 16. Mesoproterozoic rocks result from Geon 11 continental rifting, producing volcanic and sedimentary rocks of the Keweenawan Supergroup and plutonic rocks of the Midcontinent Rift Intrusive Supersuite.