|
The 400 km long Eger Rift is one of the major extensional structures in Central Europe and is associated with abundant Tertiary to Quaternary volcanic rocks occurring both within the rift and mainly on its NW uplifted flank. Geochemical and isotopic data from lavas covering the whole rift are presented. Primitive lavas predominate with compositions ranging from alkali basalts to nephelinites and melilitites. Lavas in the rift basin show similar Si-undersaturation, incompatible element enrichment, and Sr, Nd, and Pb isotope compositions as rocks on the flanks of the Eger Rift suggesting similar degrees of partial melting and mantle sources. Crustal assimilation is abundant and increases with evolution of the magmas. The Eger Rift crosses several different lithospheric units but no systematic change of magma sources appears to be related to the boundaries between the units. The Sr, Nd, and Pb isototopic compositions of the Cenozoic alkaline basalts differ from those of Cretaceous lamprophyres occurring in the same area. This suggests that the Cenozoic melts rather form from asthenospheric than from the lithospheric mantle. Three different mantle sources can be defined in the Eger Rift magmas where one is regionally restricted whereas the other two also contribute to Tertiary lavas in the northwest of the Eger Rift (Rhoen, Westerwald, Vogelsberg). The most common of these end-members resembles the suggested FOZO composition. A significant increase in the (Ce/Yb)N occurs west of about 13.5°E along the Eger Rift and apparently corresponds to the narrowing of the rift basin, i.e. less extension in its western part.
|
