Summary
The results of microprobe analyses of clinopyroxenes from alkaline melasyenites and layered melagabbros, produced by intra-plate magmatism of Paleocene age at Punta delle Pietre Nere, are here given and discussed.
The analysed pyroxenes range from diopsidic to acmite-rich compositions.
The first crystallized pyroxenes (diopside) show AlVI contents suggesting shallow depths of crystallization. In addition pyroxenes from melasyenite and those from melagabbro display different Cr contents, Al/Ti and Mg/(Mg+Fe2++Fe3+) ratios confirming their crystallization from melts produced by different parental liquids.
Diopsides and salites show an overall trend towards high Al, Ti and Fe3+, suggesting that the crystallization occurred under decreasing SiO2/Al2O3 ratios and under relatively highpH2O−pO2 conditions.
Pyroxenes from the Pietre Nere melasyenite show a progressive variation towards acmite rich compositions at Mg/(Mg+Fe2++Fe3+) lower than 0.5; those from the layered melagabbro, instead, show a continuous enrichment in Ca Fe3+ AlSiO6. This different behaviour is due to the co-crystallization, with the latest pyroxenes, of phases with different K/Na and Si/Al ratios.
Zusammenfassung
Es werden die Ergebnisse der Mikrosonden-Untersuchungen von Klinopyroxenen aus Alkali-Melasyeniten und schichtigen Alkali-Melagabbros, die durch “Intra-plate”-Magmatismus paläozenen Alters auf Punta delle Pietre Nere entstanden sind, beschrieben und erörtert.
Die untersuchten Pyroxene reichen von diopsidischen bis zu Akmit-reichen Zusammensetzungen.
Die zuerst kristallisierten Pyroxene (Diopsid) zeigen AlVI-Gehalte, die auf geringe Tiefe des Kristallisationsvorganges hinweisen. Dazu zeigen die Pyroxene aus dem Melasyenit und aus dem Melagabbro unterschiedliche Cr-Gehalte; die Al/Ti- und Mg/(Mg+Fe2++Fe3+)-Verhältnisse bestätigen deren Kristallisation aus Schmelzen, die aus unterschiedlichen Ursprungsmagmen stammen.
Die Diopside und Salite zeigen eine einheitliche Tendenz zu hohem Al-, Ti- und Fe3+-Gehalt; dies deutet darauf hin, daß die Kristallisation unter abnehmenden SiO2/Al2O3-Verhältnissen und unter relativ hohenpH2O−pO2-Bedingungen stattfand.
Die Pyroxene aus dem Punta delle Pietre Nere-Melasyenit zeigen eine zunehmende Änderung zu Akmit-reichen Zusammensetzungen bei weniger als 0,5 Mg/(Mg+Fe2++Fe3+); die Pyroxene aus dem schichtig differenzierten Melagabbro zeigen dagegen eine allmähliche Zunahme von CaFe3+AlSiO6. Dieses unterschiedliche Verhalten rührt daher, daß Mineralphasen mit unterschiedlichen K/Na- und Si/Al-Verhältnissen zugleich mit den zuletzt gebildeten Pyroxenen kristallisierten.
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References
Akasaka, M., Onuma, K., 1980: The join CaMgSi2O6−CaFeAlSiO6−CaTiAl2O6 and its bearing on the Ti-rich fassaitic pyroxenes. Contr. Min. Petrol.71, 301–312.
Aoki, K., 1964: Clinopyroxenes from alkaline rocks of Japan. Amer. Min.49, 1199–1223.
De Fino, M., La Volpe, L., Piccarreta, G., 1981: Geochemistry and petrogenesis of the paleocene platform magmatism at Punta delle Pietre Nere (Southern Italy). N. Jb. Min. Abh. (In press.)
Finger, L. W., 1972: The uncertainty in the calculated Ferric iron content of a microprobe analysis. Carnegie Inst. Washington71, 600–603.
Frisch, T., Schmincke, H., 1969: Petrology of clinopyroxene-amphibole inclusions from the Roque Nublo volcanics, Gran Canaria, Canary Islands (petrology of Roque Nublo volcanics, I). Bull. Vulcanol.33, 1073–1088.
Gibb, F. G. F., 1973: The zoned clinopyroxenes of the Shiant Isles Sill, Scotland. J. Petrol.14, 203–230.
Gupta, A. K., Onuma, K., Yagi, K., Lidiak, E. G., 1973: Effect of silica concentration on the diopsidic pyroxenes in the system diopside CaTiAl2O6−SiO2. Contr. Min. Petrol.41, 333–344.
Hamilton, D. L., Anderson, G. M., 1967: Effect of water and oxygen pressures on the crystallization of basaltic magmas. In: Basalt (Hess, H. H., Poldervaart, A., eds.), pp. 445–482. New York: Interscience Publishers.
Hamm, H. M., Vieten, K., 1971: Zur Berechnung der kristallchemischen Formel und des Fe3+-Gehaltes von Klinopyroxenen aus Elektronenstrahl-Mikroanalysen. N. Jb. Min. Mh.7, 310–314.
Hanson, G. N., 1977: Geochemical evolution of the suboceanic mantle. J. Geol. Soc. London134, 235–253.
Hawkesworth, C. J., Vollmer, R., 1979: Crustal contamination versus enriched mantle:143Nd/144Nd and87Sr/86Sr evidence from the Italian volcanics. Contr. Min. Petrol.69, 151–165.
Kushiro, I., 1969: Clinopyroxene solid solutions formed by reactions between diopside and plagioclase at high pressure. Min. Soc. Amer. Spec. Pap.2, 179–191.
Lloyd, F. E., Bailey, P. K., 1975: Light element metasomatism of the continental mantle: the evidence and consequences. Physics and Chemistry of the Earth9, 389–416.
Magonthier, M. C., Velde, D., 1976: Mineralogy and petrology of some Tertiary leuciterhonite basanites from central France. Min. Mag.40, 817–826.
Marinelli, G., 1975: Magma evolution in Italy. C. H. Squyres, the Earth Sci. Soc. of the Libyan Arab Republic, Tripoli.
Nash, W. P., Wilkinson, J. F. G., 1970: Shonkin Sag Laccolith, Montana. I. Mafic minerals and estimates of temperature, pressure, oxygen fugacity and silica activity. Contr. Min. Petrol.25, 241–269.
Papike, J. J., Cameron, K., Baldwin, K., 1974: Amphiboles and pyroxenes: characterization of other than quadrilateral components and estimates of ferric iron from microprobe data. Geol. Soc. Am., abstract with programs6, 1053–1054.
Thompson, R. N., 1972: Oscillatory and sector zoning in augite from a Vesuvian lava. Carnegie Inst. Wash. Year Book71, 463–470.
Vollmer, R., 1976: Rb−Sr and U−Th−Pb systematics of alkaline rocks: the alkaline rocks of Italy. Geochim. Cosmochim. Acta40, 283–295.
Yagi, K., 1966: The system acmite-diopside and its bearing on the stability relations of natural pyroxenes of the acmite-hedembergite series. Amer. Min.51, 976–1000.
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De Fino, M., La Volpe, L. & Piccarreta, G. Crystallization trends of pyroxenes from alkaline subvolcanites of Punta delle Pietre Nere (Gargano, Southern Italy). TMPM Tschermaks Petr. Mitt. 29, 177–192 (1982). https://doi.org/10.1007/BF01084641
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DOI: https://doi.org/10.1007/BF01084641