| State | Michigan |
|---|---|
| Name | Dickinson Group, undivided |
| Geologic age | Late Archean |
| Lithologic constituents |
Major
Metamorphic > Amphibolite
Metamorphic > Metasedimentary > Metaclastic > Metasandstone > Metagraywackemetaarkose, metagraywacke
Metamorphic > Schist
Minor
Metamorphic > Gneiss
|
| Comments | Continental margin assemblage (north of Niagara Fault). Secondary unit description from USGS Geologic Names lexicon (ref. MI016): Present in the Lake Superior region gneiss terrane of northwestern MI. Metamorphosed strata include arkose, graywacke, schist, and amphibolite--latter found in uppermost units. These apparently grade laterally and vertically into the informally designated unit, gneiss at Granite Bluffs, as well as into other unnamed granitic gneisses. Unconformably overlies the informally designated unit, granite gneiss of the Norway Lake area. Correlation chart. Is assigned a Late Archean age on the basis of radiometric dates from the East Branch Arkose (formation rank) together with the presence of inclusions of schist and quartzite in the gneiss at Norway Lake (informal). |
| References | Sims, P.K., 1992, Geologic map of Precambrian rocks, southern Lake Superior region, Wisconsin and northern Michigan: U.S. Geological Survey Miscellaneous Investigations Map I-2185, scale 1:500,000.https://pubs.er.usgs.gov/publication/i2185 USGS Geologic Names lexicon found at: http://ngmdb.usgs.gov/Geolex/https://ngmdb.usgs.gov/Geolex/search |
| NGMDB product | |
| Counties | Dickinson - Iron |