Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Volcanostratigraphy and Geochemistry of the České středohoří Mts. basaltic rocks
Abstract
The České středohoří Mts. is an erosional relict of the Cenozoic volcanosedimentary complex in the Ohře Rift. The geochemical investigation was used to test a new volcanological model. The following volcanostratigraphical formations of superficial volcanics were recognized: 1) the Lower Formation - lavas and volcanics of basanitic character (36-26 Ma, 12% norm. Ol; Mg=65-82, aver. 75; high contents of Cr, Ni, Co, Sc; common presence of lherzolite xenoloths; low 87Sr/86Sr = 0.7033128-0.703526; high 143Nd/144Nd = 0.512738-0.512849, Nd= +2.8 to + 4.8) corresponding to low-differentiated, only weakly crust-contaminated upper mantle products; 2) the Upper Formation - lavas and pyroclastics of trachybasaltic type (31-25 Ma, 2% norm. Ol: Mg=60-72, aver. 65; low contents of Cr, Ni, Co, Sc; lack of lherzolite xenoliths; higher 87Sr/86Sr = 0.704428-0.704649; lower 143Nd/144Nd = 0.512679-0.512742, Nd=+1.5 to + 2.6) representing differential and partly crust-contamined evolved products; 3) the probable Uppermost Formation - flow(s) of basanite (24 Ma) similar in geochemical characteristics to those of the Lower Formation. The Group 4) of the Late Miocene Intrusives (13 Ma) similar to those of the - Lower Formation (13 Ma, 16% norm. Ol; Mg=70-79, aver. 75; high contents of Cr, Ni, Co, Sc; somewhat higher 87Sr/86Sr = 0.703651 - 0.703761; somewhat lower 143 Nd/144 Nd = 0.512845 - 0.512847, Nd = +4.4 to + 4.3) primitive magma probably associated with rejuvenation of tectonic movements in the OR or pulsation of magmatic activity, was used for comparison.
