The Petrogenesis of Pliocene Alkaline Volcanic Rocks from the Pannonian Basin, Eastern Central Europe

• Published in: Journal of petrology 1993-04, Vol.34 (2), p.317-343
• Main Authors: EMBEY-ISZTIN, A., DOWNES, H., JAMES, D. E., UPTON, B. G. J., DOBOSI, G., INGRAM, G. A., HARMON, R. S., SCHARBERT, H. G.
• Format: Article
• Language: English
• Subjects: Crystalline rocks; Earth sciences; Earth, ocean, space; Exact sciences and technology; Igneous and metamorphic rocks petrology, volcanic processes, magmas; Isotope geochemistry; Isotope geochemistry. Geochronology
• ISSN: 0022-3530; 1460-2415
• DOI: 10.1093/petrology/34.2.317

Late Tertiary post-orogenic alkaline basalts erupted in the extensional Pannonian Basin following Eocene-Miocene subduction and its related calc-alkaline volcanism. The alkaline volcanic centres, dated between 11⋅7 and 1⋅4 Ma, are concentrated in several regions of the Pannonian Basin. Some are near the western (Graz Basin, Burgenland), northern (Nógrád), and eastern (Transylvania) margins of the basin, but the majority are concentrated near the Central Range (Balaton area and Little Hungarian Plain). Fresh samples from 31 volcanic centres of the extension-related lavas range from slightly hy-normative transitional basalts through alkali basalts and basanites to olivine nephelinites. No highly evolved compositions have been encountered. The presence of peridotite xenoliths, mantle xenocrysts, and high-pressure megacrysts, even in the slightly more evolved rocks, indicates that differentiation took place within the upper mantle. Rare earth elements (REE) and 87Sr/86Sr, 143Nd/144Nd, δ18O, δD, and Pb isotopic ratios have been determined on a subset of samples, and also on clinopyroxene and amphibole megacrysts. Sr and Nd isotope ratios span the range of Neogene alkali basalts from western and central Europe, and suggest that the magmas of the Pannonian Basin were dominantly derived from asthenospheric partial melting, but Pb isotopes indicate that in most cases they were modified by melt components from the enriched lithospheric mantle through which they have ascended. δ18O values indicate that the magmas have not been significantly contaminated with crustal material during ascent, and isotopic and trace-element ratios therefore reflect mantle source characteristics. Incompatible-element patterns show that the basic lavas erupted in the Balaton area and Little Hungarian Plain are relatively homogeneous and are enriched in K, Rb, Ba, Sr, and Pb with respect to average ocean island basalt, and resemble alkali basalts of Gough Island. In addition, 207Pb/204Pb is enriched relative to 2O6Pb/204Pb. In these respects, the lavas of the Balaton area and the Little Hungarian Plain differ from those of other regions of Neogene alkaline magmatism of Europe. This may be due to the introduction of marine sediments into the mantle during the earlier period of subduction and metasomatism of the lithosphere by slab-derived fluids rich in K, Rb, Ba, Pb, and Sr. Lavas erupted in the peripheral areas have incompatible-element patterns and isotopic characteristics different from