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| Title: | RI-31 Pre-Penokean Igneous and Metamorphic Rocks, Benton and Stearns Counties, Central Minnesota |
| Authors: | Dacre, George A.
Himmelberg, Glen R.
Morey, G.B. |
| Issue Date: | 1984 |
| Publisher: | Minnesota Geological Survey |
| Citation: | Dacre, G.A., Himmelberg, G.R. and Morey, G.B., 1984, Pre-Penokean Igneous and Metamorphic Rocks, Benton and Stearns Counties, Central Minnesota, Minnesota: Minnesota Geological Survey Report of Investigations 31, 16 p. |
| Series/Report no.: | RI
31 |
| Abstract: | The pre-Penokean igneous and metamorphic rocks in Benton and Stearns
Counties, central Minnesota, include the Richmond Gneiss and three units of
formational status that were assigned to the Sauk Rapids Metamorphic Complex
{Morey, 1978)--the Sartell Gneiss and mafic enclaves within it, the Watab
Amphibolite, and the St. Wendel Metagabbro.
Petrologic data reported here support the contention that both the
Sartell Gneiss and the Richmond Gneiss may be northern extensions of lower
and middle Archean gneisses typically developed in the Minnesota River
Valley. The Richmond Gneiss is interpreted as a syntectonic pyroxenebearing
quartz monzonite, with many similarities to charnockite, that underwent
magmatic crystallization under conditions of the granulite grade. The
Sartell Gneiss is a dominantly metasedimentary unit whose mineral assemblages
are indicative of the granulite grade. In contrast, the mafic
enclaves within the Sartell Gneiss have textures and mineral assemblages
that are unequivocally igneous. Because they are intrusive into the gneiss,
the enclaves may be considerably younger.
It is proposed here that the descriptor Sauk Rapids t1etamorphic Complex
be abandoned, and that the names Watab Amphibolite and St. Wendel Metagabbro
be replaced by the more general and less formal terms Metadiabase near Watab
and glartz Gabbro of St. Wendel Township. The stratigraphic position of the
Quartz Gabbro of St. Wendel Township is uncertain. However, the Metadiabase
near Wa tab is most likely correlative with mafic volcanic and hypabyssal
rocks in the Animikie basin that are early Proterozic in age. |
| Permanent URL: | http://purl.umn.edu/60725 |
| ISSN: | 0076-9177 |
| Appears in Collections: | Report of Investigations
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| mgs-251.pdf | | 750Kb | PDF | View/Open |
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