Depleted subcontinental lithospheric mantle and its tholeiitic melt metasomatism beneath NE termination of the Eger Rift (Europe): the case study of the Steinberg (Upper Lusatia, SE Germany) xenoliths

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 Alpoor (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).

Crustal lithology vs. thermal state and Moho heat flow across the NE part of the European Variscan orogen: a case study from SW Poland

“…spinel peridotite facies). The case studies of mantle xenolith suites from the area (Puziewicz et al 2011;Matusiak-Małek et al 2010, 2014, 2017aKukuła et al 2015) show that the lava flow through the mantle was channelized in fissures of centimetric to decimetric thickness, and the melt percolated pervasively in the neighbouring mantle peridotite. To model this situation, we assume that the discussed hypothetical mantle was instantly injected with melt.…”

Subcontinental lithospheric mantle beneath Central Europe

“…The data presented in this paper come from published (Puziewicz et al 2011;Ćwiek et al 2013;Kukuła et al 2013;Matusiak-Małek et al 2014) and unpublished studies. Modal composition of peridotites from Księginki and Krzeniów was estimated by using digital method of image analysis by Higgins (2000) and that of peridotites from other localities by JMicroVision software on high-resolution scans of one thick section per xenolith.…”

Lithospheric mantle beneath NE part of Bohemian Massif and its relation to overlying crust: new insights from Pilchowice xenolith suite, Sudetes, SW Poland

“…This mantle domain is dominated by depleted harzburgites, overprinted by "Fe-metasomatism" and subsequently by alkaline silicate or silicate-carbonate metasomatism related to Cenozoic alkaline volcanism (Puziewicz et al 2015). Numerous local variations in rock composition and style of their metasomatic overprint occur within the Lower Silesian mantle domain (e.g., Puziewicz et al 2011;Matusiak-Małek et al 2014;Kukuła et al 2015a). The study of individual xenolith suites contribute to the detailed characteristics of lithospheric mantle, enabling better insight into its geological history.…”