International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

WHOLE-ROCK CHEMISTRY AND GENETIC TYPOLOGY OF THE WEST-CARPATHIAN VARISCAN GRANITES

Pages: 79 - 90

Authors: IGOR BROSKA, PAVEL UHER

Abstract: The geochemistry of 166 new whole-rock analyses from West-Carpathian Variscan granitic rocks are presented on the basis of their division into four principal groups: S-, I-, A- and specialized S-type (SS). The contribution shows some discrimination diagrams which are useful for the recognition of these principal granite groups and also give a possible outline of the geodynamic scenario of their origin. All studied groups belong to mainly crustal aluminic (SS-, S-type) and aluminocafemic (I-, A-, partly S-type) associations, mantle-derived cafemic dioritic rocks are rare. Generally, the S- and I-type groups show predominantly Na2O/K2O ratio > 1, whereas A- and SS-type granites usually exhibit Na2O/K2O < 1. I-types are more Si-poor and Fe, P-rich than other groups, however, a part of the SS-type group belongs to the P-rich evolved granites (>0.2 wt. % P2O5) and the A-types are generally very poor in P. The Zr vs. SiO2 diagram clearly discriminates Zr and Si-rich hypersolvus A-type from other groups, similarly the A-types show the highest Zr/Hf-ratio and Y contents (>20 ppm). Ba-Sr and Sr-Rb diagrams successfully divide plagioclase-rich I-type from S,A-type and especially from K,Na-feldspar-rich SS-type. The newly modified Rb-Ba-Sr diagram reliably discriminates the groups: poorly (I, S), mildly (S, A, rarely I) and strongly evolved granites (SS, rarely S and A) were recognized. REE rock/chondrite normalized diagram discriminate all groups: REE-rich I-type without Eu-anomaly, from REE-rich A-type with negative Eu-anomaly and REE-poor S- and especially SS-type with pronounced negative Eu-anomaly. In this sense of the geotectonic position, the S- and I-type can be considered as orogenic granites, in contrast, the A-type and SS type granites are post-orogenic members.

Keywords: Western Carpathians, geochemistry, granitic rocks, S-types, I-types, A-types, Ss - types

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