Geologic units in Itasca county, Minnesota

Foliated to gneissic tonalite, granodiorite, and diorite (Neoarchean) at surface, covers 23 % 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.

Mafic metavolcanic rocks (Neoarchean) at surface, covers 15 % of this area

Mafic metavolcanic rocks. Includes minor volcaniclastic and hypabyssal intrusive rocks metamorphosed to lower greenschist to lower amphibolite facies; includes the Ely Greenstone (~2,722 Ma).

Slate and graywacke (Paleoproterozoic) at surface, covers 11 % of this area

Slate and graywacke. Includes the Rove (~1,836 to 1,777 Ma), Virginia (~1,832 Ma near base), and Thompson Formations (youngest zircons in the Thompson Formation ~1,790 Ma).

Coleraine Formation (Late Cenomanian) at surface, covers 9 % of this area

Conglomerate, lignite, sandstone, and shale; shallow marine and non-marine. Late Cenomanian age is inferred. Despite exposures in mines on the Mesabi Iron Range, the position of much of the unit contact is highly speculative.

Calc-alkalic volcanic and volcaniclastic rocks (Neoarchean) at surface, covers 9 % of this area

Calc-alkalic volcanic and volcaniclastic rocks.

Granitic intrusion (Neoarchean) at surface, covers 7 % 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.

Volcaniclastic rocks of felsic to intermediate composition (Neoarchean) at surface, covers 6 % of this area

Volcaniclastic rocks of felsic to intermediate composition.

Granite to granodiorite (Neoarchean) at surface, covers 6 % of this area

Granite to granodiorite. Variably magnetic.

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

Granitoid intrusion. Constrained solely by low gravity and magnetic signatures.

Syenite, monzodiorite, granodiorite, and diorite (Neoarchean) at surface, covers 4 % of this area

Syenite, monzodiorite, granodiorite, and diorite. Commonly hornblende- or pyroxene-bearing; Includes the Coon Lake, Side Lake, and Linden (~2,666 Ma) plutons of north-central Minnesota.

Gunflint (~1,878 Ma), Biwabik, and Emily Iron Formations (Paleoproterozoic) at surface, covers 1 % of this area

Locally includes thin basal sandstone and conglomerate. Capped by an irregular layer of brecciated iron-formation and ejecta derived from the 1,850 Ma Sudbury meteorite impact.

Magnetic intrusions, undifferentiated (Archean) at surface, covers 0.9 % of this area

Magnetic intrusions, undifferentiated. Typically too small to ascertain gravity expression.

Gabbro, peridotite, pyroxenite, lamprophyre, and metamorphic equivalents (Neoarchean) at surface, covers 0.9 % 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.

Mafic to ultramafic (komatiitic) volcanic rocks (Neoarchean) at surface, covers 0.5 % of this area

Mafic to ultramafic (komatiitic) volcanic rocks. Includes the Newton Lake Formation and Deer Lake sequence.

Granitic to granodioritic orthogneiss (Neoarchean) at surface, covers 0.5 % of this area

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

Volcanogenic graywacke and mudstone (Neoarchean) at surface, covers 0.3 % of this area

Volcanogenic graywacke and mudstone. Includes the Lake Vermilion Formation.

Pokegama Quartzite (Paleoproterozoic) at surface, covers 0.3 % of this area

Includes conglomerate and siliceous mudstone.

Mafic to ultramafic hypabyssal intrusive complexes composed of gabbro, pyroxenite, diorite, and anorthosite (Neoarchean) at surface, covers 0.3 % of this area

Mafic to ultramafic hypabyssal intrusive complexes composed of gabbro, pyroxenite, diorite, and anorthosite. Includes the Mentor and Deer Lake complexes, intrusions of the Newton Lake Formation, all within the Wawa subprovince; and the UBD intrusion (~2,685 to 2,695 Ma) in the Wabigoon subprovince.

Virginia Formation (Paleoproterozoic) at surface, covers < 0.1 % of this area

Slate and graywacke with thin carbonate layers.

Conglomerate, lithic sandstone, and graywacke, undifferentiated (Neoarchean) at surface, covers < 0.1 % of this area

Conglomerate, lithic sandstone, and graywacke, undifferentiated. Includes the Midway sequence, Seine Group, and a part of the Knife Lake Group known as the Ogishkemuncie conglomerate that contains clasts of ~2,690 Ma Saganaga Tonalite (unit Ast). Deposition of alluvial fan and fluvial sediments occurred in fault-bounded basins.

Granodiorite to hornblende diorite, locally magmatically foliated (Neoarchean) at surface, covers < 0.1 % 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.