Petrological And Seismic Studies Of The Lithosphere In The Earthquake Swarm Region Vogtland-Nw Bohemia, Central Europe
Journal Article: Petrological And Seismic Studies Of The Lithosphere In The Earthquake Swarm Region Vogtland-Nw Bohemia, Central Europe
AbstractNew petrological and geochemical data of upper mantle and lower crustal xenoliths from a Quaternary tephra deposit in M_tina, Czech Republic, are discussed in the frame of previous geophysical results (receiver functions, reflection seismology) of the western Eger/Ohre Rift area. The Vogtland/NW Bohemia region is well known for intraplate earthquake swarms, which are usually associated with volcanic activity. As previously reported, 3He/4He data of CO2 emissions in mofettes and mineral-water springs point at ongoing magmatic processes in this area. Using teleseismic P receiver functions, an approximately 40-km-wide Moho updoming (from 31 to 27 km) and indications for a seismic discontinuity at 50 to 60 km depth were observed beneath the active CO2-degassing field. The studied xenolith suite probes a lithospheric profile within the structural and gas geochemical anomaly field of the western Eger Rift. With regard to texture, composition, p-T estimates and origin, five xenolith groups can be discriminated. Upper crustal xenoliths (quartzites, phyllites, mica schists) resemble crystalline country rocks at surface. One noritic xenolith (6 kbar, 800°C) could represent a sample of the lower crust. Clinopyroxenites and hornblendites probably represent cumulates of the nephelinitic magma or fragments of magmatic veins. Porous wehrlites and one hornblende peridotite xenolith reflect a metasomatied upper mantle. Megacrysts of Ti-rich amphibole, olivine, clinopyroxene, and phlogopite could be fragments of pegmatitic veins or high-pressure phenocrysts. Most of the ultramafic nodules (xenoliths and megacrysts) formed at pressures between 6 and 11 kbar (22 to 38 km depth), at temperatures well above regional geotherms of the Bohemian Massif calculated from surface heat flow studies. Orthopyroxene-bearing spinel-lherzolite xenoliths were not observed. Our petrographical, geochemical, and thermobarometric results indicate a lithospheric mantle strongly altered by magmatic processes. This metasomatism can cause slower than typical uppermost-mantle seismic velocities in a greater area and might help to explain observed seismic anomalies.
- W. H. Geissler, H. Kampf, W. Seifert and P. Dulski
- Published Journal
- Journal of Volcanology and Geothermal Research, 2007
- Not Provided
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W. H. Geissler,H. Kampf,W. Seifert,P. Dulski. 2007. Petrological And Seismic Studies Of The Lithosphere In The Earthquake Swarm Region Vogtland-Nw Bohemia, Central Europe. Journal of Volcanology and Geothermal Research. (!) .