Geologic units in Chippewa county, Minnesota

Granitic orthogneiss and migmatite (Mesoarchean to Paleoarchean) at surface, covers 38 % of this area

Granitic orthogneiss and migmatite. Geophysical map patterns imply this unit intruded other gneisses.

Granitoid gneiss with dioritic to amphibolitic enclaves (Mesoarchean to Paleoarchean) at surface, covers 24 % of this area

Granitoid gneiss with dioritic to amphibolitic enclaves. Produces moderately high and varied gravity and magnetic signatures.

Undifferentiated (Cenomanian to Campanian) at surface, covers 14 % of this area

Conglomerate, sandstone, mudstone, shale, marlstone, siltstone, and minor lignite, deposited in marine and non-marine settings; likely Cenomanian to Campanian age. Unit outline is the product of contouring the stratigraphic top and base, from which an isopach grid was created. Because the distribution is patchy, unit boundaries were drawn from the gridded data to represent locations where more than 25 feet (8 meters) of thickness occurs. As a result, many areas outside of the unit boundaries may be overlain by thin Cretaceous strata and the unit is depicted without a contact line.

Leucogranite (Neoarchean) at surface, covers 6 % of this area

Leucogranite. Occurs along the Yellow Medicine Shear Zone and elsewhere, primarily in batholithic settings.

Gabbro, pyroxenite, diorite, and lamprophyre (Paleoproterozoic) at surface, covers 4 % of this area

Gabbro, pyroxenite, diorite, and lamprophyre. Includes the Watab quartz diorite (~1,780 Ma), St. Wendell quartz gabbro, and an unnamed diorite (~1,786 Ma).

Granitic intrusion of unknown age (Archean or Paleoproterozoic) at surface, covers 4 % of this area

Granitic intrusion of unknown age. Low gravity and magnetic expression.

Foliated to gneissic tonalite, granodiorite, and diorite (Neoarchean) at surface, covers 4 % of this area

Foliated to gneissic tonalite, granodiorite, and diorite. Includes the Lookout Mountain tonalite (~2,718 Ma) of the Giants Range batholith and other intrusions within batholithic complexes defined by a low-to-moderate gravity signature with magnetic foliation apparent from aeromagnetic maps.

Granodiorite to hornblende diorite, locally magmatically foliated (Neoarchean) at surface, covers 2 % of this area

Granodiorite to hornblende diorite, locally magmatically foliated. Includes the Britt Granodiorite (~2,685 Ma) and other intrusions having moderate gravity and magnetic signatures.

Gabbro, peridotite, pyroxenite, lamprophyre, and metamorphic equivalents (Neoarchean) at surface, covers 1 % of this area

Gabbro, peridotite, pyroxenite, lamprophyre, and metamorphic equivalents. Includes the Oaks intrusion (~2,671 Ma) in the Wabigoon subprovince, and a ~2,639 Ma lamprophyre in the western Wawa subprovince; locally defined by variably high gravity and magnetic signatures.

Granitic intrusion (Neoarchean) at surface, covers 1.0 % of this area

Granitic intrusion. Includes the Sacred Heart (~2592, 2,603 Ma) and Ortonville granites, the Shannon Lake Granite (~2,674), and other intrusions having low gravity and magnetic signatures.

Gabbroic to dioritic intrusion (Archean or Paleoproterozoic) at surface, covers 0.6 % of this area

Gabbroic to dioritic intrusion. High to moderate gravity and magnetic signature. Includes Providence and Cottonwood intrusions in southwestern Minnesota.

Amphibolitic to dioritic gneiss (Mesoarchean to Paleoarchean) at surface, covers 0.4 % of this area

Amphibolitic to dioritic gneiss.

Mafic intrusions including pyroxenite, peridotite, gabbro, and lamprophyre (Paleoproterozoic) at surface, covers 0.3 % of this area

Mafic intrusions including pyroxenite, peridotite, gabbro, and lamprophyre. Defined largely by magnetic signature. One intrusion in Morrison County is ~1,791 Ma, and lithologically similar intrusions cut the Foley Granite (~1,774 Ma).

Granitic to granodioritic orthogneiss (Neoarchean) at surface, covers 0.1 % of this area

Granitic to granodioritic orthogneiss. Includes the McGrath Gneiss (~2,752 ± 15, 2,557 Ma) and unnamed units.

Mylonite, varied protolith (Archean) at surface, covers < 0.1 % of this area

Mylonite, varied protolith. Age of shearing unknown and likely protracted.