Magnetite banded iron formation (Soudan Iron-Formation, Neoarchean, ~2.722 Ga; Rt. 169 roadcut between Soudan & Robinson, Minnesota, USA) 2 : 無料・フリー素材/写真
Magnetite banded iron formation (Soudan Iron-Formation, Neoarchean, ~2.722 Ga; Rt. 169 roadcut between Soudan & Robinson, Minnesota, USA) 2 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | Magnetite BIF in the Precambrian of Minnesota, USA.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 GreenstoneRadiometric dating of Ely Greenstone rocks (see Jahn & Murthy, 1975 and Jirsa et al., 2010) indicates that the Soudan Iron-Formation is about 2.722 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 magnetite BIF, characterized by alternating layers of blackish magnetite (Fe3O4) and silvery-gray specular hematite (Fe2O3).Stratigraphy: Soudan Iron-Formation member, Ely Greenstone, Vermilion Greenstone Belt, Neoarchean, ~2.722 GaLocality: 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)-------------------------References cited:Jahn & Murthy (1975) - Rb-Sr ages of the Archean rocks from the Vermilion District, northeastern Minnesota. Geochimica et Cosmochimica Acta 39: 1679-1689.Jirsa et al. (2010) - Geologic map of Minnesota, Precambrian bedrock geology, description of map units. Minnesota Geological Survey State Map Series S-22. |
| 撮影日 | 2015-06-10 09:19:47 |
| 撮影者 | James St. John |
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