IMMOBILE TRACE ELEMENTS DISCRIMINATION DIAGRAMMS WITH ZEOLITIZED VOLCANICLASTICS FROM THE EVROS - THRACE - RHODOPE VOLCANIC TERRAIN
The Rhodope and Evros areas of the Thrace Region in north-eastern Greece and the adjusted areas in Bulgaria are characterized by wide spread volcanic formations of Upper Eocene to Miocene in age. The volcaniclastic materials associated with such formations have, in some cases, undergone inter alia a notable zeolitization process. The mineralogy of the altered volcaniclastics is often dominated by clinoptilolite -heulandite type of minerals. The Winchester and Floyd (1977) plots indicating rhyodacite/dacite to trachyandesite parent materials, while the similar diagram, as modified by Pearce (1986), indicate andesite to trachyandesite precursors. The alkalinity index (Nb/Y ratio) seems to coincide between the two types of diagrams, but, there is a notable difference of the differentiation index, i.e. the Zr/TiO2 ratio. The Th-Co diagram (Hastie et al., 2007) unfolds a clearer picture for the nature of the precursors and reveals a clear progression of a calc-alkaline to a high-K calc alkaline affinity of the parental volcanic materials.