File:Pumiceous orendite lamproite (Pleistocene, 1.30-1.37 Ma; Black Rock volcanic center, Leucite Hills, Wyoming, USA) 7 (48980828858).jpg
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[edit]DescriptionPumiceous orendite lamproite (Pleistocene, 1.30-1.37 Ma; Black Rock volcanic center, Leucite Hills, Wyoming, USA) 7 (48980828858).jpg |
Pumiceous orendite lamproite in the Pleistocene of Wyoming, USA. Southwestern Wyoming's Leucite Hills are a group of Pliocene to Pleistocene volcanic centers that erupted lamproite lavas, a rare extrusive igneous lithology. Based on chemistry and mineral content, the Leucite Hills lamproite lavas have been categorized as wyomingite, orendite, or madupite. This is an exposure of orendite lamproite lava at Black Rock, a volcanic center in the eastern Leucite Hills. Orendite is a diopside-sanidine-phlogopite lamproite having leucite, diopside pyroxene, phlogopite mica, sanidine, plus minor hornblende amphibole and rutile. Lavas at Black Rock include orendites and olivine orendites, the latter having noticeable to subtle, scattered olivine xenocrysts. Either lithology may be non-vesicular or vesicular (with fairly small vesicles) or pumiceous. Black Rock orendites have had their groundmass leucite partially altered to analcime. Sedimentary xenoliths of varying sizes are fairly common. Small, dark red objects are often seen - most are non-vitreous in luster and resemble jasper, while some are vitreous - I suspect they are all garnet xenocrysts (?). Chemical analysis has shown that orendite is mafic (50 to 56 wt.% silica), magnesian (<11 wt.%), potassium-rich (~10-12%), and sodium-poor. The orendites at this locality are inferred to have been derived from lherzolite-harzburgite mantle rocks that were metasomatically enriched in phlogopite veins at >1.2 Ga (the latter event may have been caused by Precambrian subduction along the Wyoming Craton margin). Volcanism in the Leucite Hills may possibly be due to mantle melting by the subsurface fringe areas of the Yellowstone Hotspot track. Age: Pleistocene, 1.30 to 1.37 Ma Locality: northern slopes of Black Rock, eastern Leucite Hills Volcanic Province, Great Divide Basin, northeast of the town of Superior, southwestern Wyoming, USA (41° 52' 26.02" North, 108° 47' 41.13" West) Example references on Leucite Hills geology: Lange, R.A., I.S.E. Carmichael & C.M. Hall. 2000. 40Ar/39Ar chronology of the Leucite Hills, Wyoming: eruption rates, erosion rates, and an evolving temperature structure of the underlying mantle. Earth and Planetary Science Letters 174: 329-340. Schultz, A.R. & W. Cross. 1912. Potash-bearing rocks of the Leucite Hills, Sweetwater County, Wyoming. United States Geological Survey Bulletin 512. 39 pp. |
Date | |
Source | Pumiceous orendite lamproite (Pleistocene, 1.30-1.37 Ma; Black Rock volcanic center, Leucite Hills, Wyoming, USA) 7 |
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@N05/48980828858 (archive). It was reviewed on 7 November 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
7 November 2019
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Horizontal resolution | 180 dpi |
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Software used | Adobe Photoshop Elements 16.0 (Macintosh) |
File change date and time | 13:16, 29 October 2019 |
Y and C positioning | Co-sited |
Exif version | 2.21 |
Date and time of digitizing | 15:02, 6 June 2012 |
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Date metadata was last modified | 09:16, 29 October 2019 |
Unique ID of original document | 5D8A8528549F32514536CAE1A360CB28 |