Dickinson Group, undivided

Metavolcanic and metasedimentary rocks in Dickinson County, Mich. From youngest to oldest, consists of Six-Mile Lake Amphibolite, Solberg Schist, and East Branch Arkose.
State Michigan
Name Dickinson Group, undivided
Geologic age Late Archean
Lithologic constituents
Metamorphic > Amphibolite
Metamorphic > Metasedimentary > Metaclastic > Metasandstone > Metagraywackemetaarkose, metagraywacke
Metamorphic > Schist
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).
NGMDB product
Counties Dickinson - Iron