K-Ar DATING OF THE PALEOGENE LATE EXTENSIONAL MAGMATISM IN THE EASTERN RHODOPES

ABSTRACT. During the Paleogene, as a result of extension, the Central Rhodope, Kesibir and Byala reka domes formed in the Eastern Rhodopes. The East Rhodope depression, a domain of intensive intermediate and acid volcanism, is located between them and Harmanli block. Subvolcanic bodies and dikes occur in the neighboring domes. The conclusions are based on all K-Ar data of the authors (84) and those from accessible literature sources (87) for the discussed magmatism. The results for individual magmatic phases (complexes) are dispersed within an unrealistically large time interval – 7-8 Ma. However, their mean arithmetic values are close to data from more precise (Rb-Sr, Ar-Ar) methods. The time span of the Paleogene late-extensional magmatism is 42.7-25.5 Ma or 39.9.-27.3 Ma as indicated by the mean values for the individual phases. There is a tendency for migration of the magmatism from the intermediate magmatic groups from NW to SE: 39,9-32,