File:Jaspilite banded iron formation (Soudan Iron-Formation, Neoarchean, ~2.69 Ga; Rt. 169 roadcut between Soudan & Robinson, Minnesota, USA) 5 (18417567614).jpg
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[edit]DescriptionJaspilite banded iron formation (Soudan Iron-Formation, Neoarchean, ~2.69 Ga; Rt. 169 roadcut between Soudan & Robinson, Minnesota, USA) 5 (18417567614).jpg |
Jaspilite BIF in the Precambrian of Minnesota, USA. (geology hammer for scale) The Soudan Iron-Formation is a Neoarchean-aged banded iron formation (BIF) unit in the Vermilion Greenstone Belt of northeastern Minnesota, USA. Stratigraphically, the Soudan is considered to be the middle member of the Ely Greenstone. Metamorphosed pillow basalt successions occur above and below the iron-rich interval: - upper member of the Ely Greenstone - Soudan Iron-Formation member - lower member of the Ely Greenstone Radiometric dating of Ely Greenstone rocks (see Jahn & Murthy, 1975) indicates that the Soudan Iron-Formation is about 2.69 billion years old. The Soudan Iron-Formation was deposited in a deep-water environment and is closely associated with several types of volcanic rocks formed in an ancient island arc setting. As such, the unit is classified as an Algoma-type iron-formation. Superior-type iron-formations were deposited in relatively shallow water, continental shelf settings. The Soudan Iron-Formation is exposed in & around the town of Soudan, Minnesota at roadcuts, glacially-eroded outcrop knobs, surface mines, and underground mines. Observed iron-rich lithologies in the Soudan Iron-Formation include specularite, jaspilite BIF, and magnetite BIF. The outcrop shown above is jaspilite BIF, characterized by alternating layers of silvery-gray specular hematite (Fe2O3) and reddish-colored ferruginous chert ("jasper"). Stratigraphy: Soudan Iron-Formation member, Ely Greenstone, Vermilion Greenstone Belt, Neoarchean, ~2.69 Ga Locality: roadcut on the northern side of Rt. 169, just west of milepost 270, between the towns of Soudan and Robinson, north of Fourmile Lake & southeast of Lake Vermilion's Armstrong Bay, northeastern Minnesota, USA (47° 50' 32.14" North, 92° 09' 19.59" West) Reference cited: Jahn & Murthy (1975) - Rb-Sr ages of the Archean rocks from the Vermilion District, northeastern Minnesota. Geochimica et Cosmochimica Acta 39: 1679-1689. |
Date | |
Source | Jaspilite banded iron formation (Soudan Iron-Formation, Neoarchean, ~2.69 Ga; Rt. 169 roadcut between Soudan & Robinson, Minnesota, USA) 5 |
Author | James St. John |
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This image was originally posted to Flickr by jsj1771 at https://flickr.com/photos/47445767@N05/18417567614. It was reviewed on 19 July 2015 by FlickreviewR and was confirmed to be licensed under the terms of the cc-by-2.0. |
19 July 2015
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Date metadata was last modified | 18:15, 21 June 2015 |
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