Rock-forming minerals of alkaline volcanic series associated with the Cheb-Domažlice Graben, West Bohemia | Szegedi Tudományegyetem, Ásványtani, Geokémiai és Kőzettani Tanszék

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Mai névnapok:

Kende, Eufrozina

Rock-forming minerals of alkaline volcanic series associated with the Cheb-Domažlice Graben, West Bohemia

Acta Mineralogica-Petrographica, Szeged 2002, Vol. 43, pp. 1-18

J. Ulrich
Novák J.K.
F. E. Lloyd
Balogh K.
Buda György

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 recognised: (i) weakly alkaline series basanite – trachybasalt – (basaltic) trachyandesite – trachyte – rhyolite (15.9-11.4 Ma) and (ii) strongly alkaline series olivine nephelinite – tephrite (16.5-8.3 Ma). The chemistry of the minerals characteristically reflects the differentiation development of the above rock series. Early crystallization in the mafic rocks is manifested by olivine phenocrysts (Fo66-76), melilite, Timagnetite and (Ti,Fe3+)-diopside to fassaite; in the intermediate rocks by diopside; and in the felsic rocks by (Mn,Ti)-magnetite, diopside, and high-temperature K-oligoclase (phenocryst cores). Continuing to late crystallisation in mafic to intermediate rocks is represented by kaersutite, nepheline (at T <700oC; also occurs with melilite in ijolite pegmatoidal segregations) and labradorite to andesine, with K-andesine to K-oligoclase rims in transitional rocks. In the felsic compositions, ongoing crystallisation is characterised by Mn-magnesioriebeckite, Mn-winchite and Mg-biotite; feldspars are prevalently anorthoclase (perthite), which occasionally mantles K-oligoclase and is succeeded by Na-sanidine (matrix or rare rims to anorthoclase phenocrysts). Feldspars and quartz in the matrix of the felsic rocks terminate crystallization. Late magmatic minerals are analcime, replacing plagioclase and nepheline, carbonates and barite in the mafic rocks. Mnoxyhydroxide, nontronite, rare sulphur and organic matter reflect crystallization in the postmagmatic stage.




acta2002, alkaline volcanism, Bohemia, Cheb-Domažlice Grabben, magnetite, Rock-forming minerals




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