File:Amphibolite inclusions in Giants Range Batholith (Neoarchean, 2.674-2.682 Ga; Confusion Hill roadcut, just north of Virginia, Minnesota, USA) 1 (23640848356).jpg
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Amphibolite inclusion in tonalite & diorite in the Precambrian of Minnesota, USA. Light-colored rock = tonalite Dark-colored rock = diorite Irregularly-shaped black masses = amphibolite This is part of a famous outcrop in northeastern Minnesota - Confusion Hill. These are intrusive igneous rocks of Late Archean age, part of the Giants Range Batholith. The dark-colored material is diorite, a phaneritic, intermediate intrusive rock composed principally of sodic plagioclase feldspar, hornblende amphibole, and biotite mica. Other minerals that can be in diorite include pyroxene, minor quartz, minor potassium feldspar, and various trace minerals. The light-colored rock is tonalite, a phaneritic, felsic intrusive igneous rock having sodic plagioclase feldspar, quartz, and one or more mafic minerals such as amphibole and pyroxene. Lithologies intermediate between tonalite and diorite (i.e., quartz diorite) are also present at this site (see Peterson et al., 2005). Some specific sites at this outcrop show that tonalite intrudes diorite, while in other areas of the same outcrop, the diorite intrudes the tonalite. This mutually cross-cutting relationship is consistent with magma mingling during emplacement (Peterson et al., 2005). The irregularly-shaped, black-colored masses seen above are amphibolite (metabasalt), which are metamorphosed basalt lava flows that predate intrusion of the Giants Range Batholith. Metamorphosed sedimentary rocks are also present as inclusions at the Confusion Hill Outcrop. Geologic unit & age: Giants Range Batholith, Neoarchean, 2.674-2.682 Ga [The light-colored tonalite is part of the Lookout Mountain Tonalite, which is a component of the Giants Range Batholith.] Locality: Confusion Hill outcrop - roadcut on the eastern side of northbound Rt. 169/Rt. 53, immediately north of roadside rest stop, northwestern side of Lookout Mountain, Laurentian Divide, just north of the town of Virginia, central St. Louis County, northeastern Minnesota, USA (47° 34' 40.71" North, 92° 32' 37.21" West) Site-specific info. from: Peterson et al. (2005) - Architecture of an Archean greenstone belt: stratigraphy, structure and mineralization. Minnesota Geological Survey Guidebook 21: 154-180. |
| Date | |
| Source | Amphibolite inclusions in Giants Range Batholith (Neoarchean, 2.674-2.682 Ga; Confusion Hill roadcut, just north of Virginia, 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@N05/23640848356 (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. |
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| current | 05:53, 5 December 2019 | | 4,000 × 3,000 (4.44 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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