Geochemistry of the high-K calc-alkaline basaltic sills and dykes in the South Rhodope Massif (N Greece)

In this paper mafic sills and dykes found in Palaeogenic sedimentary rocks of the South Rhodope Massif (Greece) are studied. Their mineralogy is represented mainly by plagioclases (An₄₅-An₈₈), amphiboles (Mg-hornblende, Mg-hastingsite) and clinopyroxenes of salitic compositions with subordinate biotite. Chemistry and corresponding discriminant diagrams (Ti-Zr-Y, Ti-Zr-Sr) and discriminant functions (F₁-F₂ from pyroxene) classify them as basalts and basaltic andesites of the high-K calc-alkaline rocks series. According to their geochemical and petrological features an orogenic nature results for the rocks in study. REE abundances show an enrichement of LREE and a moderate fractionation in HREE patterns. The above together with the non significant europium anomalies (Eu/Eu*=0,92–0,85) and the relatively high contents of K, Ba and Sr in these rocks indicate a magma genesis by partial melting of an upper mantle source already enriched in LILE. A K-Ar determination on hornblende phenocrysts gave a Lower Oligocene age (33,5±1.2 m.y.) which is in accordance with the age of the andesitic lavas extended to the northwest of the studied area.