File:Basalt lava flows (North Shore Volcanic Group, Mesoproterozoic, ~1.1 Ga; Leif Ericson Park, Duluth, Minnesota, USA) 2 (22427571782).jpg
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Basalt lava flows in the Precambrian of Minnesota, USA. Along the northern shore of western Lake Superior are numerous exposures of a lava flow-dominated succession called the North Shore Volcanic Group. This is equivalent to & the same age as the Portage Lake Volcanic Series of northern Michigan's Keweenaw Peninsula (<a href="https://www.flickr.com/photos/jsjgeology/albums/72157632266738191">www.flickr.com/photos/jsjgeology/albums/72157632266738191</a>). The North Shore and Portage Lake successions are ~1.1 billion years old and represent basalt lava flows, plus minor sedimentary rocks, that filled up an ancient rift valley. This old rift is the Lake Superior segment of the Mid-Continent Rift System, a tear in the ancient North American paleocontinent of Laurentia (see: <a href="https://minerals.usgs.gov/science/midcontinent-rift-minerals/images/MRS-map.png" rel="nofollow">minerals.usgs.gov/science/midcontinent-rift-minerals/imag...</a>). Tectonic rifting started along this tear, exactly like the modern-day East African Rift Valley. Laurentia's Mid-Continent Rift System started and then stopped and was subsequently filled and buried. This ancient failed rift is now exposed on either side of Lake Superior in North America's Great Lakes. The outcrop shown above is part of the Leif Ericson Park Lavas, which consist of basalt, basaltic andesite, and icelandite (= ferro-andesite) (Miller et al., 2001). Stratigraphy: Leif Ericson Park Lavas, Upper Southwest Sequence, North Shore Volcanic Group, Keweenawan Supergroup, upper Mesoproterozoic, ~1099 Ma Locality: Lake Superior shoreline exposure in Leif Ericson Park, just northeast of the city of Duluth, northeastern Minnesota, USA Reference cited: Miller et al. (2001) - Geologic map of the Duluth Complex and related rocks, northeastern Minnesota. Minnesota Geological Survey Miscellaneous Map Series M-119. |
| Date | |
| Source | Basalt lava flows (North Shore Volcanic Group, Mesoproterozoic, ~1.1 Ga; Leif Ericson Park, Duluth, Minnesota, USA) 2 |
| 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@N05/22427571782. 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. |
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| current | 00:17, 10 October 2019 | | 3,000 × 3,723 (3.73 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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