Structural geology of the Knife Lake area of northeastern Minnesota

Gruner, John W.; Dutton, C. E.; Gibson, George R.; Grout, Frank F.

doi:10.1130/gsab-52-1577

Cited by 25 publications

(16 citation statements)

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“…In Cache Bay there are remarkable exposures of conglomerate composed of pebbles, cobbles, and boulders of the tonalite almost to the exclusion of other rock types. The conglomerate interfingers with the graywacke-argillite which rests directly on the tonalite south of Cache Bay, as mapped by Gruner (1941). The Knife Lake beds dip at high angles (65° to 75°) to the west.…”

Section: Knife Lake Groupmentioning

confidence: 94%

“…The geology of this region is known through the investigations of Grout (1929Grout ( , 1936, Tanton (1931Tanton ( , 1938, and Gruner (1941). The Saganaga Lake-Northern Light Lake area is a classical one that has figured prominently in the development of the Precambrian chronology in Minnesota (Grout and others, 1951).…”

Section: Previous Workmentioning

confidence: 99%

“…Alkalic syenodiorite and granodiorite which Grout (1936) indicated on his map as younger syenite are described here under the informal name of Icarus pluton. The metasedimentary rocks of Cache Bay are referred to the Knife Lake Group (series), following the earlier designation of Gruner (1941).…”

Section: Nomenclaturementioning

confidence: 99%

“…1). South of Sea Gull Lake, Gruner (1941Gruner ( , p. 1593) mapped a conglomerate succeeding the greenstone and assigned it to his unit 4, "Jasper Lake greenstone conglomerate or agglomerate" of the Knife Lake Group. He had some reservations, however, about its stratigraphic position and considered the possibility of the conglomerate being a fragmental phase of the greenstone.…”

Section: Greenstone and Related Rocksmentioning

confidence: 99%

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Early Precambrian Rocks in the Saganaga Lake-Northern Light Lake Area, Minnesota-Ontario Part I. Petrology and Structure

Goldich¹,

Hanson²,

Hallford³

et al. 1972

Geological Society of America Memoirs

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The Precambrian rocks, older than 2,600 m.y., in the Saganaga Lake-Northern Light Lake area on the Minnesota-Ontario boundary include a thick succession of metavolcanic rocks, chiefly greenstone but with some intermediate to silicic types, and minor metasediments; the Northern Light Gneiss; the Saganaga Tonalite; alkalic syenodiorite and granodiorite; and the Knife Lake Group. A variety of dikes and sills in the older units are of different ages; the youngest are related to the Keweenawan igneous activity, approximately 1,100 m.y. ago. 151on May 27, 2015 memoirs.gsapubs.org Downloaded from GOLDICH AND OTHERSThe Northern Light Gneiss consists principally of fine-grained biotite leucotonalite, or trondhjemite, that is interlayed with amphibolite and lesser amounts of metarhyodacite and metarhyolite. The gneiss is part of the volcanic pile of greenstone and related rocks formerly referred to the Keewatin.Both the greenstone and the Northern Light Gneiss were intruded by the Saganaga Tonalite. This rock was formerly called the Saganaga Granite, but the "granite" is a sheared and altered phase in which microcline was introduced, and small amounts of epidote, chlorite, sericite, and carbonate were formed at the expense of the primary hornblende, biotite, and oligoclase.The Saganaga Tonalite and the Northern Light Gneiss were intruded by a small pluton near Icarus Lake in the eastern part of the area. The pluton consists of a western phase of syenodiorite and an eastern phase of somewhat younger granodiorite. Both rocks are alkalic and are characterized by soda-rich pyroxene and amphibole.Two periods of folding in the region were previously recognized as the Laurentian and Algoman orogenies. The Saganaga Tonalite is a late-kinematic intrusion in the folded greenstone and related rocks. Uplift and vigorous erosion uncovered the tonalite which supplied large boulders and finer detritus to the sediments of the Knife Lake Group deposited on the western margin of the batholith. At Cache Bay the conglomerate resting on the tonalite is composed almost wholly of clasts of tonalite, but north of Cache Bay the conglomerate on the greenstone is composed largely of pieces derived from the greenstone and related rocks. The tonalite also supplied a large component of the graywacke-argillite sequence that is intercalated with the conglomerate at Cache Bay.The Knife Lake conglomerate and graywacke-argillite sequences were folded during the Algoman orogeny, and at Cache Bay the beds dip approximately 70° W. Although these events were deciphered from the geologic record, efforts to resolve the two periods of folding by radiometric age determinations have not been completely successful. The Saganaga Tonalite is dated by a whole-rock Rb-Sr isochron and by U-Pb ages on sphene and zircon at 2,730 m.y. The older Northern Light Gneiss probably was formed not more than 2,750 m.y. ago, and the younger Icarus pluton was emplaced approximately 2,700 m.y. ago; hence a complicated geologic history is encompassed in a span of 50 m.y. or less.The Saga...

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Section: Knife Lake Groupmentioning

confidence: 94%

Section: Previous Workmentioning

confidence: 99%

Section: Nomenclaturementioning

confidence: 99%

Section: Greenstone and Related Rocksmentioning

confidence: 99%

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Early Precambrian Rocks in the Saganaga Lake-Northern Light Lake Area, Minnesota-Ontario Part I. Petrology and Structure

Goldich¹,

Hanson²,

Hallford³

et al. 1972

Geological Society of America Memoirs

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“…Volcanic and plutonic rocks range in age from 2.75 to 2.69 Ga and from 2.74 to 2.65 Ga, respectively (Card, 1990, and references therein). Paleo protero zoic plutonic rocks intrude along the southeastern margin of the study area (Gruner, 1941;Jirsa and Miller, 2004).…”

Section: Geologic Settingmentioning

confidence: 99%

Application of Lidar to resolving tectonic and glacial fabrics in glaciated terrain: An example from an Archean granite-greenstone belt, northeastern Minnesota

Dyess

Hansen

2014

Geosphere

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In this study we examine an Archean granite-greenstone terrane in northeastern Minnesota (USA) to illustrate the application of high-resolution Lidar (light detection and ranging) altimetry to mapping regional tectonic fabrics in forested glaciated areas. We describe the recognition of lineaments and distinguish between tectonic and glacial lineament fabrics. We use a 1-m Lidar derived bare earth digital elevation model to construct multiple shaded-relief images for lineament mapping with sun elevation of 45° and varying sun azimuth in 45° intervals. Two suites of lineaments are apparent. Suite A has a unimodal orientation, mean trend of 035, and consists of short (< 2 km long) lineaments within sediment deposits and bedrock. Suite B lineaments, which are longer (1-30 km) than those of suite A, have a quasi-bimodal orientation distribution, with maximum trends of 065 and 090. We interpret suite A as a surfi cial geomorphologic fabric related to glaciation, and suite B as a proxy for the regional tectonic fabric. Field measurements of regional tectonic foliation trajectories are largely consistent with suite B lineaments across the study area. Although not all suite B lineaments correlate to mapped structures, our analysis demonstrates that high-resolution Lidar altimetry can be useful in mapping regional tectonic fabrics in glaciated terrane.

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