File:Metamorphosed pillow basalt (Ely Greenstone, Neoarchean, ~2.722 Ga; large loose block at Ely visitor center, Ely, Minnesota, USA) 1 (21266644269).jpg
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DescriptionMetamorphosed pillow basalt (Ely Greenstone, Neoarchean, ~2.722 Ga; large loose block at Ely visitor center, Ely, Minnesota, USA) 1 (21266644269).jpg |
Metamorphosed pillow basalt in the Precambrian of Minnesota, USA. The boulder shown above is a large glacial erratic of Ely Greenstone, a distinctive and famous unit in northeastern Minnesota. Greenstone is a metamorphic rock typically dominated by the minerals plagioclase feldspar and chlorite, plus often actinolite and epidote. Before metamorphism, greenstone was basalt or gabbro - both are mafic igneous rocks. The above rock used to be basalt - it was part of an underwater lava flow. The bulbous structures seen in this specimen are pillows, which are diagnostic of underwater basaltic lava flow eruptions. Pillow basalts can be observed forming underwater in today's oceans at basaltic volcanic sites such as Hawaii. The smoothed surface of individual pillows was produced by glacial erosion during the Pleistocene Ice Age. Geologic unit & age: upper member of the Ely Greenstone, Neoarchean, ~2.722 Ga Locality: glacial erratic on display on the grounds of the Ely visitor center, immediately southwest of the Rt. 1-Rt. 169 intersection in the eastern part of the town of Ely, northeastern St. Louis County, northeastern Minnesota, USA (47° 54' 10.61" North, 91° 50' 30.75" 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. |
Date | |
Source | Metamorphosed pillow basalt (Ely Greenstone, Neoarchean, ~2.722 Ga; large loose block at Ely visitor center, 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@N05/21266644269 (archive). It was reviewed on 10 October 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
10 October 2019
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current | 00:16, 10 October 2019 | 3,158 × 2,591 (3.4 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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Camera manufacturer | Canon |
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Date and time of data generation | 17:10, 9 June 2015 |
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Image title | |
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Horizontal resolution | 180 dpi |
Vertical resolution | 180 dpi |
Software used | Adobe Photoshop Elements 13.0 (Macintosh) |
File change date and time | 21:37, 15 September 2015 |
Y and C positioning | Co-sited |
Exif version | 2.21 |
Date and time of digitizing | 17:10, 9 June 2015 |
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White balance | Auto white balance |
Digital zoom ratio | 1 |
Scene capture type | Landscape |
Lens used | 6.2-18.6 mm |
Date metadata was last modified | 15:37, 15 September 2015 |
Unique ID of original document | 4CAD8FA4F3AF70170745B0C9717528C9 |
IIM version | 17,987 |