Petrogenesis of the Oligocene volcanics from the Central Rhodope massif (N. Greece)
European Journal of Mineralogy Volume 7 Number 5 (1995), p. 1169 - 1182
published: Oct 5, 1995
manuscript accepted: Apr 18, 1995
manuscript received: Feb 28, 1994
ArtNo. ESP147050705011, Price: 29.00 €
Abstract The Oligocene volcanic rocks of the Central Rhodope massif range in composition from basalts to rhyolites, and belong to orogenic calc-alkaline and shoshonite series. These lavas were erupted during an extensional tectonic event, in a post-collisional setting. The eastern part of the massif, the Kotani-Kalotycho area, includes mainly basic to intermediate rocks (basalts, basaltic andesites, high-K andesites, latites, trachytes), whereas the western part, the Dipotama-Kotyli and Zarkadenia areas, is of larger extent and consists of acid rocks only (high-K dacites, rhyolites). Mineralogical, petrological and geochemical data supported by isotopic data (87Sr/86Sr ratios 0.706-0.707 and δ18O values ranging mainly from + 6.2 ‰ to + 7.7 ‰) indicate that the basic to intermediate rocks evolved predominantly by assimilation/fractional crystallization of a parental magma which originated at the mantle-crust boundary according to the MASH hypothesis of Hildreth & Moorbath (1988). Geochemical data and Sr and O isotope ratios (0.708-0.709 and + 8.8 ‰ to + 12.9 ‰, respectively), as well as the geological evidence, do not favour a genetic link between the acid and the basic to intermediate rocks that can be explained by simple fractional crystallization. Instead, disequilibrium phenocryst assemblages in the high-K dacites and many of the rhyolites lead to the conclusion that these rocks were mainly derived by mixing of a basic and an anatectic silicic magma. The basaltic magma which triggered the crustal melting is considered consanguineous with the parental liquid feeding the Kotani-Kalotycho basic to intermediate lavas.