Algoman revolution. Term applied by A.C. Lawson to a pre-Cambrian epoch of granitic intrusion which he considered to have immediately preceded the formation of the †Animikie rocks, but which some other geologists place at a lower horizon in the Huronian series, and which still other geologists regard as Laurentian. (See USGS Bull. 769, p. 123-124). C.K. Leith, R.J. Lund, and A. Leith, 1935 (USGS Prof. Paper 184), placed it below lower Huronian and above Knife Lake series (tentatively classified as pre-Huronian and post-Laurentian, but which may eventually prove to be lower Huronian).

Source: US geologic names lexicon (USGS Bull. 896, p. 31).

The younger of two periods of deformation and magmatic activity distinguished by Lawson (1888, 1913). In his view, the Laurentian rocks (older) were intruded into a dominantly metasedimentary sequence (called the Coutchiching) that in turn was overlain by a dominantly metavolcanic sequence (called the Keweetin). After a period of erosion, a second metasedimentary sequence (called the Seine) was deposited and it, as well as the older rocks, was deformed a second time when the Algoman intrusions were emplaced. The concept of a two-fold subdivision separated by a post-Laurentian unconformity persisted well into the middle of the 20th Century. However, any volcanic-sedimentary sequence in the Superior province may consists of a single mafic to felsic to sedimentary assemblage, or it may consist of one or more assemblages repeated in space and time. All major rock-forming events in the Rainy Lake area of northern MN (Lake Superior region) and southern ON occurred between about 2,700 and 2,600 m.y. age. Peterson and others (1972) obtained a younger Rb-Sr age for the so-called Algoman granites of 2,485 +/-90 m.y. Such discrepancies between older U-Pb, and apparently younger Rb-Sr whole rock, potassium-argon, and Rb-Sr mineral ages are common in the greenstone-granite terrane of northern MN. Age of Algoman is considered Late Archean. Correlation chart.

Source: GNU records (USGS DDS-6; Denver GNULEX).