Petrology and geochemistry of the Tertiary alkaline intrusive rocks at Doupov, Doupovské hory Volcanic Complex (NW Bohemian Massif)
Abstract
Geochemical variations suggest that the essexitic rocks and sodalite syenitoids do not form a common evolutionary line with nephelinolites. Nephelinolites are isotopically close to the EAR or CMR compositions and interaction of their parental magmas with the continental crust was negligible.
Magmatic evolution of nephelinolites was dominated by fractionation of clinopyroxene accompanied at the early stage by olivine and later by titanite, magnetite and apatite. Essexite is isotopically more different though still within the field of mafic lavas from DHVC.
Either its parental magma originated in heterogeneous mantle with more distinct lithospheric signature or this magma reacted with the continental crust during its ascent and fractionation. Sodalite monzosyenite displays significantly higher 87Sr/86Sr ratios.
The K–Ar ages of intrusive rocks from Doupov are 30–29 Ma.