File:Monchiquite lamprophyre dike (Precambrian; Michipicoten River Bridge South roadcut, south of Wawa, Ontario, Canada) 39 (47926932003).jpg
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| Description |
Monchiquite lamprophyre in the Precambrian of Ontario, Canada. At this locality, granodiorites of the Mission Stock have been intruded by unusual igneous dikes composed of dark gray-colored monchiquite lamprophyre and orangish-red microsyenite. Monchiquites are very rare igneous rocks with highly unusual mineralogies. The name comes from the type locality in the Monchique Range of Portugal. Monchiquite is a type of lamprophyre that lacks feldspar and instead has feldspathoid (at this site, the feldspathoid mineral is analcime). The mineralogy of monchiquites usually consists of olivine, clinopyroxene, biotite mica, amphibole, analcime, and sometimes nepheline or leucite. [Info. from Massey, 1985, pp. 42-43.]: The rocks at this outcrop near Wawa, Ontario are ocellar lamprophyres with phenocrysts and xenocrysts of olivine in a groundmass of titanomagnetite, Al-pyroxene, Ti-phlogopite, with a mesostasis of analcime, Fe-rich pyroxene, and calcite. Reported xenoliths include Cr-spinel hartzburgite and garnet-spinel wehrlite. They have a black color on fresh surfaces and are brownish-weathering. This dikes in this area show evidence of multiple and composite intrusions. The age of the monchiquite is probably Proterozoic, and possibly late Mesoproterozoic. Massey (1985) and Wilson (2006) suggest that these dikes were emplaced at about the same time as the nearby Firesand River Carbonatite Complex, which dates to 1.078 Ga. Locality: Michipicoten River Bridge South Outcrop - roadcut on the western & eastern sides of Route 17, south of the Michipicoten River bridge & northeast of Roller Lake, south-southwest of the town of Wawa, Michipicoten Greenstone Belt, Ontario, southeastern Canada (47° 54' 54.46" North latitude, 84° 48' 35.46" West longitude) (= stop 7 of Wilson (2006) - Unusual Archean Diamond-Bearing Rocks of the Wawa Area, p. 28.) Reference cited: Massey (1985) - Geology of the Mishewawa Lake area, District of Algoma. Ontario Geological Survey Open File Report 5532. 167 pp. 15 figs. 6 tables. 20 pls. 4 maps. |
| Date | |
| Source | Monchiquite lamprophyre dike (Precambrian; Michipicoten River Bridge South roadcut, south of Wawa, Ontario, Canada) 39 |
| 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@N05/47926932003 (archive). It was reviewed on 6 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 | 01:39, 6 December 2019 | | 2,736 × 3,442 (7.97 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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