Contrasting Sodic and Potassie Glassy Inclusions in Apatite Crystals from an Ijolite |
| |
Authors: | LE BAS M J; ASPDE J; WOOLLEY A R |
| |
Institution: | 1 Department of Geology, University of Leicester Leicester LEI 7RH, England
2 Department of Mineralogy, British Museum (Natural History) London SW7 5BD, England |
| |
Abstract: | Electron probe analysis of isotropic to weakly birefringentglassy inclusions in apatite crystals within the Usaki ijoliteof western Kenya, indicates that two contrasting compositionsexist. These inclusions are thought to represent samples oforiginal silicate melts. One is rich in K2O(6 weight per cent),poor in Na2O(0.3 weight per cent), and oversaturated with respectto silica; and the other is rich in Na2O(614 weight percent), poor in K2O(0.2 weight per cent), has an antipatheticrelation between Na2O and CaO (together they usually total 15weight per cent) and is undersaturated with respect to silica.One inclusion shows these two compositions co-existing, apparentlyin an immiscible relationship. Other inclusions show compositionsintermediate between the Na-rich and K-rich types, and theyare interpreted as the result of reduced immiscibility. Thepresence of halides and calcium phosphate is considered to enhancethe immiscibility process. The parental composition, estimatedon a volatile-free basis is: SiO2 54.9, Al2O3, 27.4, CaO 7.3,Na2O 3.4, K2O 6.9, which corresponds to a lime-rich aluminoussyenite. |
| |
Keywords: | |
本文献已被 Oxford 等数据库收录! |
|