Columnar-jointed orendite lamproite lava (Pleistocene, 1.30-1.37 Ma; Black Rock volcanic center, Leucite Hills, Wyoming, USA) 17 : 無料・フリー素材/写真
Columnar-jointed orendite lamproite lava (Pleistocene, 1.30-1.37 Ma; Black Rock volcanic center, Leucite Hills, Wyoming, USA) 17 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | 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.Volcanism in this area may possibly be due to Yellowstone Hotspot fringe melting of the mantle. The lamproites appear to be derived from lherzolite-harzburgite mantle rocks that were metasomatically enriched in phlogopitic veins at >1.2 Ga (the latter may be caused by Precambrian subduction along the Wyoming Craton margin).Seen here is a volcanic center in the eastern Leucite Hills called Black Rock. It is composed of olivine orendite. Orendite is a diopside-sanidine-phlogopite lamproite having leucite, diopside pyroxene, phlogopite mica, sanidine, plus minor hornblende amphibole and rutile. Chemical analysis shows that orendite is mafic (50 to 56 wt.% silica), magnesian (<11 wt.%), potassium-rich (~10-12%), and sodium-poor. Orendite at Black Rock has had its groundmass leucite partially altered to analcime. Olivine occurs as occasional to scattered xenocrysts.The photo shows the summit of Black Rock, which consists of columnar-jointed orendite lava. Columnar jointing is most common in basalt lava flows (e.g., Giant's Causeway in Ireland and Devils Postpile in California), but it also occurs in other lithologies (e.g., porphyritic phonolite at Devils Tower, Wyoming). It forms as lava cools and contracts, forming polygonal columns.Age: Pleistocene, 1.30 to 1.37 MaLocality: Black Rock, eastern Leucite Hills Volcanic Province, Great Divide Basin, northeast of the town of Superior, southwestern Wyoming, USA (41° 52' 26.98" North, 108° 47' 42.39" 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. |
| 撮影日 | 2012-06-06 15:19:45 |
| 撮影者 | James St. John |
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