STRONTIUM ISOTOPE STUDIES OF THE LATE ALPINE EXTENSIONAL MAGMATISM IN EASTERN RHODOPES

Significant differences in the character of distribution of the initial strontium ratios ( 87 Sr/ 86 Sr)i between the medium acid and the acid magmatic groups (subgroups) of the late extensional magmatism are not observed. This fact may be discussed as indication for a common origin of the initial magmas from the different regions of distribution of this magmatism and of the peripheral magmatic chambers, respectively. The relatively low values of the initial strontium ratios ( 87 Sr/ 86 Sr)i for this magmatism is an indication for mantle origin. The higher values of this ratio in the initial phases of magmatism are probably a result of more pronounced pollution of the initial magma with crustal material. The latest phases of the magmatism, however, are weakly enriched or barren of crustal material and thus their initial strontium ratios e close to 0.704, which correlates with the values of this ratio for the contemporary mantle.