Coexisting Miocene alkaline volcanic series associated with the Cheb-Domažlice Graben (W Bohemia): Geochemical characteristics

Jaromír Ulrych, Jana Štěpánková, Felicity E. Lloyd, Kadosa Balogh

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Abstract

The Middle to Late Miocene intraplate alkaline volcanism of W Bohemia is associated with the uplift of the NE flank of the Cheb-Domažlice Graben. Two coexisting cogenetic volcanic series have been recognized there: (i) weakly alkaline series (WAS) basanite-trachybasalt-(basaltic) trachyandesite-trachyte-rhyolite (15.9-11.4 Ma) and (ii) strongly alkaline series (SAS) olivine nephelinite-tephrite (16.5-8.3 Ma). Similar patterns in olivine nephelinite and basanite Primitive Mantle-normalized incompatible trace elements point to a single mantle source that was geochemically similar to Enriched Mantle. Negative Rb and K anomalics probably reflect residual amphibole in the source. Magma modelling showed that olivine nephelinite and basanite could form by different degrees of partial melting of the mantle source, with amphibole, garnet, olivine and clinopyroxene in the residuum. The mantle source was probably represented by lithospheric mantle metasomatized by plume-like material. Evolution of the SAS is limited in extent and rather unclear. The WAS is well developed and its evolution can be modelled by fractionation of olivine, clinopyroxene, Fe-Ti oxide, and a small proportion of plagioclase, and in late stages by alkali feldspar, Fe-Ti oxide, clinopyroxene and apatite. Crustal contamination cannot be ruled out but there is no substantial evidence of this in felsic derivatives.

Original languageEnglish
Pages (from-to)53-64
Number of pages12
JournalGeologica Carpathica
Volume54
Issue number1
Publication statusPublished - Feb 1 2003

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Keywords

  • Alkaline rocks
  • Geochemistry
  • Miocene volcanism
  • W Bohemia

ASJC Scopus subject areas

  • Geology

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