Summary
The mineral chemistry of the pyroxene from representative suites of leucite-bearing and related assemblages occurring in south-west Uganda, Roman Region, Australia and Antarctica is considered in terms of some serial characteristics of the host rocks. The pyroxene compositions show distinct and systematic chemical variations, which are evaluated in terms of the ratios Ti/Al and (2−Si)/Al=Td, calculated from the structural formula. Both ratios generally increase from early- to late-crystallized pyroxene compositions but the variations are typical of individual rock series and depend on the level of alkalinity of the host rocks, i.e. (Na+K)/Al and the pressure under which the pyroxene crystallized. Low Ti/Al and Td values result largely from the influence of pressure, while Ti/Al>0.5 and Td>1.0 reflect the chemistry of the host rock, particulary in terms of high (Na+K)/Al ratio. Some experimental data bearing on the genetic interpretation of the pyroxene chemistry from the above assemblages are reappraised.
Zusammenfassung
Die Mineralchemie des Pyroxens aus repräsentativen Leuzit-führenden und verwandten Gesteinen in Südwest-Uganda, in der Romana, in Australien und in der Antarktis steht in Beziehung zur Charakteristik der Muttergesteine. Die Zusammensetzungen der Pyroxene zeigen klare und systematische chemische Variationen, die auf der Basis der aus der Strukturformel berechneten Verhältniszahlen Ti/Al und (2-Si)/Al=Td bewertet werden. Beide Verhältniszahlen nehmen grundsätzlich von früh- zu spätkristallisierten Pyroxenen zu, jedoch sind diese Variationen typisch für bestimmte Gesteinsserien und abhängig vom Grad der Alkalinität des Muttergesteins, d.h. (Na+K)/Al und vom Druck unter dem der Pyroxen kristallisierte. Niedrige Ti/Al und Td-Werte resultieren vor allem aus dem Einfluß des Druckes, während Ti/Al>0,5 und Td>1,0 die chemische Zusammensetzung des Muttergesteins reflektieren, besonders im Hinblick auf hohe Na+K/Al-Verhältnisse. Einige experimentelle Daten zur genetischen Interpretation des Pyroxen-Chemismus aus den oben genannten Vorkommen werden im Lichte dieser neuen Ergebnisse betrachtet.
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References
Aoki, K., Kushiro, I., 1968: Some clinopyroxenes from ultramafic inclusions in Dreiser Weiher, Eifel. Contr. Min. Petrol.18, 326–337.
Bailey, D. K., 1969: The stability of acmite in the presence of H2O. Amer. J. Sci.267-A, 1–16.
Barton, M., Hamilton, D. L., 1979: The melting relationships of a Modupite from the Leucite Hills, Wyoming, to 30 kb. Contr. Min. Petrol.69, 133–142.
—,van Bergen, M. J., 1981: Green clinopyroxenes and associated phases in a potassium-rich lava from the Leucite Hills, Wyoming. Contr. Min. Petrol.77, 101–114.
Brown, F. H., Carmichael, I. S. E., 1969: Quaternary volcanoes of the Lake Rudolf region: The basanite-tephrite series of the Korath Range. Lithos2, 239–260.
Carmichael, I. S. E., 1967: The mineralogy and petrology of the volcanic rocks from the Leucite Hills, Wyoming. Contr. Min. Petrol.15, 24–66.
—,Nicholls, J., 1967: Iron-titanium oxides and oxygen fugacities in volcanic rocks. J. Geophys. Res.72, 4665–4687.
Cundari, A., 1973: Petrology of the leucite-bearing lavas in New South Wales. J. Geol. Soc. Austr.20, 465–492.
—, 1975: Mineral chemistry and petrogenetic aspects of the Vico lavas, Roman volcanic Region, Italy. Contr. Min. Petrol.53, 129–144.
—, 1979: Petrogenesis of leucite-bearing lavas of the Roman volcanic Region, Italy. Contr. Min. Petrol.70, 9–21.
—, 1982: Petrology of clinopyroxenite ejecta from Somma-Vesuvius and their genetic implications. Tschermaks Min. Petr. Mitt.30, 17–35.
—,Le Maitre, R. W., 1970: On the petrogeny of the leucite-bearing rocks of the Roman and Birunga volcanic Regions. J. Petrol.11, 33–47.
Dawson, J. B., Smith, J. V., Hervig, R. L., 1977: Late-stage diopside in kimberlite groundmass. N. Jb. Min. Mh.12, 529–543.
Edgar, A. D., Green, D. H., Hibberson, W. O., 1976: Experimental petrology of a highly potassic magma. J. Petrol.17, 339–356.
—,Condliffe, E., Barnett, R. L., Shirran, R. J., 1980: An experimental study of an olivine ugandite magma and mechanisms for the formation of its K-enriched derivatives. J. Petrol.21, 475–497.
Ferguson, A. K., 1973: On hour-glass sector zoning in clinopyroxene. Min. Mag.39, 321–325.
—, 1977: The natural occurrence of aegirine-neptunite solid solution. Contr. Min. Petrol.60, 247–253.
Ferguson, A. K., 1978a: Mineral chemistry and petrological aspects of some leucite-bearing lavas from Bufumbira, south-west Uganda, and related suites. Unpublished Ph.D. thesis, University of Melbourne.
—, 1978: Ca-enrichment in olivine from volcanic rocks. Lithos11, 189–194.
—,Cundari, A., 1975: Petrological aspects and evolution of the leucite-bearing lavas from Bufumbira, south-west Uganda. Contr. Min. Petrol.50, 25–46.
Ferguson, A. K., Sewell, D. K. B., 1978: An overlay program for the online operation of a JEOL JXA.5A electron microprobe using a modifiedMason et al. 2AF correction program. Dept. Geol. Univ. Melbourne, Publ. No. 5.
Hartman, P., 1969: Can Ti4+ replace Si4+ in silicates? Min. Mag.37, 366–369.
Holmes, A., Harwood, H. F., 1937: The volcanic area of Bufumbira. Part II. Mem. geol. Surv. Uganda3, 300 pp.
Lloyd, F. E., 1981: Upper-mantle metasomatism beneath a continental rift: clinopyroxenes in alkali mafic lavas and nodules from south-west Uganda. Min. Mag.44, 315–323.
Lloyd, F. H., Bailey, D. K., 1975: Light element metasomatism of the continental mantle: the evidence and consequence. Phys. Chem. Earth9, 389–416.
Mason, P. K., Frost, M. T., Reid, S. J. B., 1969: Computer programs for calculating correlations in quantitative X-ray microanalysis. Nat. Phys. Lab. (U.K.) IMS. Rep. 2.
Mattias, P. P., 1965: Lave dell'Apparato Vulsino. Per. Mineralogia34, 137–199.
Rønsbo, J. B., Pedersen, A. K., Engell, J., 1977: Titan-aegirine from early Tertiary ash layers in northern Denmark. Lithos10, 193–204.
Sheraton, J. W., Cundari, A., 1980: Leucitites from Gaussberg, Antarctica. Contr. Min. Petrol.71, 417–427.
Streckeisen, A. L., 1967: Classification and nomenclature of igneous rocks. N. Jb. Min. Abh.107, 144–214.
Thompson, R. N., 1972: Oscillatory and sector zoning in augite from a Vesuvian lava. Carnegie Inst. Wash., Yearb.71, 463–470.
—, 1974: Some high-pressure pyroxenes. Min. Mag.39, 768–787.
—, 1977: Primary basalts and magma genesis: III Alban Hills, Roman Comagmatic Province, Central Italy. Contr. Min. Petrol.60, 91–108.
Wade, A., Prider, R. T., 1940: The leucite-bearing rocks of the West Kimberley area, Western Australia. J. Geol. Soc. Lond.96, 39–98.
Washington, H. S., 1906: The Roman Comagmatic Region. Publ. Carnegie Inst. Wash. 57.
Whitford, D. J., Nicholls, I. A., Taylor, S. R., 1979: Spatial variations and geochemistry of Quaternary lavas across the Sunda arc in Java and Bali. Contr. Min. Petrol.70, 341–356.
Wimmenauer, W., 1966: The eruptive rocks and carbonatites of the Kaiserstuhl, Germany. In: Carbonatites (Gittens, J., Tuttle, O. F., eds.), pp. 183–204. New York: Interscience.
Yagi, K., Onuma, K., 1967: The join CaMgSi2O6−CaTiAl2O6 and its bearing on the titanaugites. J. Hokkaido Univ. Fac. Sci.13, 463–483.
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Cundari, A., Ferguson, A.K. Significance of the pyroxene chemistry from leucite-bearing and related assemblages. TMPM Tschermaks Petr. Mitt. 30, 189–204 (1982). https://doi.org/10.1007/BF01082329
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DOI: https://doi.org/10.1007/BF01082329