Abstract
The ca. 30 Ma Steinberg basanite occurs at the NE termination of the Eger (Ohře) Rift in the NW Bohemian Massif, Central Europe, and belongs to the Cenozoic alkaline Central European Volcanic Province. The basanite hosts a suite of mantle xenoliths, most of which are harzburgites containing relatively magnesian olivine (Fo 90.5–91.6) and Al-poor (0.04–0.13 a pfu) orthopyroxene (mg# 0.90–0.92). Some of these harzburgites also contain volumetrically minor clinopyroxene (mg# 0.92–0.95, Al 0.03–0.13 a pfu) and have U-shaped LREE-enriched REE patterns. The Steinberg harzburgites are typical for the Lower Silesian - Upper Lusatian domain of the European subcontinental lithospheric mantle. They represent residual mantle that has undergone extensive partial melting and was subsequently affected by mantle metasomatism by mixed carbonatite-silicate melts. The Steinberg xenolith suite comprises also dunitic xenoliths affected by metasomatism by melt similar to the host basanite, which lowered the Fo content in olivine to 87.6 %. This metasomatism happened shortly before xenolith entrainment in the erupting lava. One of the xenoliths is a wehrlite (olivine Fo 73 %, clinopyroxene mg# 0.83–0.85, subordinate orthopyroxene mg# 0.76–0.77). Its clinopyroxene REE pattern is flat and slightly LREE-depleted. This wehrlite is considered to be a tholeiitic cumulate. One of the studied harzburgites contains clinopyroxene with similar trace element contents to those in wehrlite. This type of clinopyroxene records percolation of tholeiitic melt through harzburgite. The tholeiitic melt might be similar to Cenozoic continental tholeiites occurring in the Central European Volcanic Province (e.g., Vogelsberg, Germany).
Highlights
Mantle xenoliths, brought to the surface by volcanic eruptions, are common in the alkaline lavas of the Cenozoic Central European Volcanic Province (CEVP)
The degree of partial melting cannot be estimated on the basis of trace element composition of clinopyroxene, its YbN/LaN ratio follows the fractional melting trend in spinel stability field defined by Norman (1998)
The xenolith suite from Steinberg in Upper Lusatia is dominated by aluminium-poor and highly magnesian harzburgites, which appear to be the dominant lithology of the Lower Silesian – Upper Lusatian domain of European lithospheric mantle
Summary
Brought to the surface by volcanic eruptions, are common in the alkaline lavas of the Cenozoic Central European Volcanic Province (CEVP). Their Bsampling^ by the erupting lavas is accidental, and their position in the vertical profile of the subcontinental lithospheric mantle (SCLM) is usually difficult to ascertain. The lateral inhomogeneity of the lithospheric mantle beneath Europe has already been documented by Downes (2001), and different lithological Bdomains^ were identified in Massif Central (Lenoir et al 2000).
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