Geochemical and Sr-Nd isotopic evidence for the genesis of the Late Cainozoic Almopia volcanic rocks (Central Macedonia, Greece)

Major and trace element contents and Sr-Nd isotope ratios of selected volcanics of Pliocene age from the Almopia area, central Macedonia, Greece, have been determined. These rocks are mainly distinguished as two groups based on geographical, petrological and isotopic data: a) the east-central western group (E-CW) and b) the south western group (SW). The absence of contemporaneous basic volcanics in the Almopia area coupled with the considerable scatter of elements in variation diagrams rule out fractional crystallization as the dominant differentiation process. Instead, disequilibrium textures along with the positive correlation of Sr-isotope ratios with differentiation suggest mixing between a basic and an acid component combined with assimilation and fractionation. The spider diagrams of the most silica-poor volcanics show evidence of subduction-related processes, indicating that the parental magmas may have been derived from partial melting of mantle wedge enriched in LILE and LREE by subducted slab-derived fluids. Previous data on the oxygen isotope composition of the same volcanics are consistent with this genetic hypothesis. Lastly, the relatively high Sr-87/Sr-86 and low Nd-143/Nd-144 ratios (0.7080 and 0.512370, respectively) of the volcanic sample inferred to be compositionally the closest one to the parental magma of Almopia rocks suggest that the incompatible element enrichment of the mantle source is old, probably of Proterozoic age.