File:Fault slickenlines in metamorphosed pillow basalt (Ely Greenstone, Neoarchean, ~2.722 Ga; Rt. 169 roadcut just east of Ely, Minnesota, USA) 1 (21341934660).jpg

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Fault slickenlines in metamorphosed pillow basalt in the Precambrian of Minnesota, USA.

This is part of an outcrop of Ely Greenstone, a distinctive and famous unit in northeastern Minnesota. The lineated, light-colored areas (partly stained orangish-brown by iron oxides) are the partially eroded remnants of a slickenlined, mineralized crust that formed in a fault zone. Faults are fractures in rocks along which differential displacement has occurred. Dip-slip faults are those involving movement of rocks in non-horizontal directions. Strike-slip faults involve movement of rocks in horizontal directions. The two common types of dip-slip faults are normal faults and reverse faults.

Fault movement results in polishing and striating of the immediately adjacent wall rocks. Fault zones can have breccias, fault gouges, slickenlined mineral crusts, or striated to polished surfaces.

Geologic unit & age: upper member of the Ely Greenstone, Neoarchean, ~2.722 Ga

Locality: outcrop on the northern side of Rt. 169, 1.3 miles east of the Rt. 1-Rt. 169 intersection, just east of the town of Ely, northeastern St. Louis County, northeastern Minnesota, USA (47° 54' 41.26" North, 91° 48' 58.70" West)


References on the Ely Greenstone:

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.
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Source Fault slickenlines in metamorphosed pillow basalt (Ely Greenstone, Neoarchean, ~2.722 Ga; Rt. 169 roadcut just east of Ely, Minnesota, USA) 1
Author James St. John

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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/21341934660 (archive). It was reviewed on 5 December 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0.

5 December 2019

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current05:48, 5 December 2019Thumbnail for version as of 05:48, 5 December 20194,000 × 3,000 (4.69 MB)Ser Amantio di Nicolao (talk | contribs)Transferred from Flickr via #flickr2commons

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