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Shoshonite is a basaltic rock, properly a potassic trachyandesite, composed of olivine, augite and plagioclase phenocrysts in a groundmass with calcic plagioclase and sanidine and some dark-colored volcanic glass. Shoshonite gives its name to the shoshonite series and grades into absarokite with the loss of plagioclase phenocrysts and into bannakite with an increase in sanidine.〔Gest, D. E. and A. R. McBirney, ''Genetic relations of shoshonitic and absarokitic magmas, Absaroka Mountains, Wyoming,'' Journal of Volcanology and Geothermal Research, Vol 6; issues 1-2, Sept 1979. pp 85-104〕 Shoshonite was named by Iddings in 1895 for the Shoshone River in Wyoming.〔(Shoshonite: Webster's Online Dictionary )〕 Textural and mineralogical features of potash-rich basaltic rocks of the absarokite-shoshonite-banakite series strongly suggest that most of the large crystals and aggregates are not true phenocrysts as previously thought but are xenocrysts and microxenoliths, suggesting a hybrid origin involving assimilation of gabbro by high-temperature syenitic magma.〔Prostka, Harold J., ''Hybrid Origin of the Absarokite-Shoshonite-Banakite Series, Absaroka Volcanic Field, Wyoming,'' 1973 GSA Bulletin February, 1973 v. 84 no. 2 p. 697-702 (abstract )〕 ==Chemical characteristics== Igneous rocks with shoshonitic chemical characteristics must be:〔Morrison, Gregg, 1980, ''Characteristics and tectonic settings of shoshonite rock association,'' Lithos, 13, 97-108〕 #Near-saturated in silica; #Low iron enrichment; #High total alkalies (Na2O + K2O > 5%); #High K2O/Na2O; #Steep positive slope for K2O versus SiO2 at low SiO2; #Enrichment in P, Rb, Sr, Ba, Pb, light rare earth elements; #Low TiO2; #High but variable Al2O3; #High Fe2O3/FeO. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Shoshonite」の詳細全文を読む スポンサード リンク
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