Summary
A new occurrence of basalt (minimum K/Ar age 57.9 ± 2.2 m.y.) is reported from Budaliget, near Budapest. Major and minor element concentrations show that the basalts are alkaline and potassic in nature ranging from olivine tholeiite to moderately undersaturated basanite. High mg-values and concentrations of Ni and Cr indicate that some of the samples may represent primary compositions. High pressure accidental xenoliths, xenocrysts and cognate megacrysts are frequent and the chemical zoning patterns of olivine and pyroxene phenocrysts indicate a complex evolution and polibaric conditions for the crystallization. The discovery of the new basalt occurrence is important from a geodynamical point of view: prior to the last two major geodynamical events (Plio-Pleistocene rifting with associated alkali basaltic volcanism and collision of microplates with associated Miocene calk-alkaline volcanism) the continental lithosphere below NE Transdanubia may have experienced another rifting period in the Paleocene or Upper Cretaceous.
Zusammenfassung
Aus der Nähe von Budapest (Budaliget) wird ein neues Basaltvorkommen (minimum K/Ar Alter 57.9 ± 2.2 m. J.) beschrieben. Die Konzentrationen der Haupt- und Spurenelemente zeigen dass die Basalte Kali-betont sind und dass sie zwischen Olivintholeiiten und mässig untersättigten Basaniten variieren. Hohe mg-Zahlen sowie Ni- und Cr-Konzentrationen sprechen dafür, dass die Proben zum Teil primäre Zusammensetzungen aufweisen. Xenolithe mit Hochdruckparagenesen, Xenokristalle und cognate Megakristalle kommen haufig vor. Der chemische Zonarbau von Olivinund Pyroxenphenokristallen deutet auf eine komplexe Kristallisationsgeschichte bei wechselnden Druck hin. Die Entdeckung dieses neuen Basaltvorkommens ist von geodynamischer Bedeutung: Vor den letzten zwei geodynamischen Ereignissen (a) Entstehung von Rifttekonik im Plio-Pleistozän mit alkalibasaltischem Vulkanismus und (b) Kollision von verschiedenen Mikroplatten begleitet von miozänem kalkalkalischem Vulkanismus war die Lithossphäre unterhalb von NE Transdanubien einer weiteren Riftperiode im Paleozän oder in der oberen Kreide ausgesetzt.
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Embey-Isztin, A., Dobosi, G., Noske-Fazekas, G. et al. Petrology of a new basalt occurrence in Hungary. Mineralogy and Petrology 40, 183–196 (1989). https://doi.org/10.1007/BF01164488
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DOI: https://doi.org/10.1007/BF01164488
Keywords:
- Alkali basalt
- peridotite xenolith
- major and trace element geochemistry
- chemical zoning in phenocrysts
- K/Ar age