Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Jaromír Ulrych, Edvín Pivec, Pavel Povondra, Jozef Rutšek

Upper-mantle xenoliths in melilitic rocks of the Osečná Complex, North Bohemia

Journal of the Czech Geological Society, volume 45 (2000), issue 1-2, 79 - 83

The melilitic Osecna Complex (79-49 Ma), located at the intersection of the Ohře Rift with the Lužice Fault in N Bohemia, originated from an upper mantle source. Associated diatremes (and maars?) filled with pelletal lapilli-ash tuff of olivine melilitite composition predate the formation of the Osečná Complex (olivine melilitolite - polzenite - melilite-bearing olivine nephelinite). Xenoliths of upper-mantle origin occur in both the massive rocks and pelletal lapilli-ash tuff of diatreme filling. Dunite to harzburgite in melilite-bearing olivine nephelinites represent depleted mantle. Glimmerite to mica clinopyroxenite in polzenite are possibly representatives of metasomatised upper mantle products. Garnet serpentinite, eclogite?, norite and ferro-dunite xenoliths are entrained from the local crystalline basement and occur in the diatreme filling only. They come from rocks of primary upper-mantle origin. The upper-mantle-xenolith suite indicates the presence of both depleted and enriched (metasomatised) upper mantle beneath the northern part of the Bohemian Massif. The associated ultramafic xenoliths of upper-mantle-derived rocks that intrude the local crystalline basement are indicative for lithospheric plate boundary.