Evolution of the Elatia plutonite (Hellenic Rhodope Massif, N. Greece)

Among the many Tertiary granitoids intruding the basement of the Hellenic R hodope Massif in northern Greece, the Elatia plutonite to-ether with its ea stern extension, known as the Skaloti-Paranesti plutonite, comprise the big gest granitic intrusion. It is an Eocene plutonite (at least 50 Ma), althou gh whole-rock Rb-Sr errorchrons give a Cretaceous age. Its main rock-type i s a medium- to coarse-grained (homblende)-biotite granodiorite (GRD) with a marginal porphyritic phase. The GRD is intruded by dykes of fine- to mediu m-grained biotite granite to leucogranite (GR) varying in thickness from se veral centimetres to several metres. The eastern part of the plutonite cons ists of a two-mica granite (TMG) which intrudes the GRD and resembles the G R. Most of the major elements in the GRID and GR display well-correlated trend s in Harker diagrams, while in the TMG they generally show trends intersect ing with the GR trends. Trace-element variation diagrams reveal distinct tr ends with no compositional gaps between GRD and GR. Subparallel (Ba, Zr, Zn , Ce) or intersecting trends (Nb) indicate that the GR cannot be considered as an petrogenic product of GRD. Subparallel trends of TMG and GR do not s upport any evolutionary relation between these two groups. The REE patterns are very similar showing quite enrichment (La-CN = 50-250) relative to cho ndrite. LREE are enriched relative to HREE in all rocks [(La/Lu)(CN) is 16- 41]. Sigma REE, (La/Lu)(CN) and Eu/Eu* decrease with differentiation. The 5 0 Ma-based Sr initial ratios ranges from 0.70613 to 0.70656 in the GRD, fro m 0.70772 to 0.70840 in the GR, and from 0.70681 to 0.70746 in the TMG, whi le the Sr initial ratios of the metamorphic basement samples range between 0.70811 and 0.71272. The delta O-18 value increases with silica content fro m 8.45 to 10.08 parts per thousand in the GRID and from 10.23 to 10.75 part s per thousand in the GR, and is 9.3 parts per thousand in the TMG. Geological relationships, mineralogy, major and trace element geochemistry, and O and Sr isotope composition tend to support that GRID, GR and TMG com prise three distinct rock groups. The existence of a genetic relation betwe en GRD and GR is ruled out by the Zr, Ba, Th, REE and Sr isotope behaviour. A genetic relation between GR and TMG is also ruled out, since they show c ross-cutting relationships, although a genetic relation is supported by the ir REE patterns and Sr isotopes. Field geology, petrographic, mineralogical and geochemical data, as well as (Sr-87/Sr-86)(0) and delta O-18 variation s suggest an ATC evolution process for the GRD. The AFC modelling employed to test this hypothesis used the trace element abundances of the less evolv ed ORD rocks as the initial composition and metamorphic rocks of the area a s assimilant. The best fit between observed and calculated values was obtai ned for r = 0.2, when gneiss (SID-2) was the assimilant. The proposed model explains satisfactorily the geochemical behaviour of the trace elements an d the Sr isotope behaviour. To explain the increase of delta O-18 within th e ORD rocks an assimilant with a hypothetical delta O-18 value of about 18 parts per thousand must be assumed. OR rocks were also evolved through an A FC process with the same assimilant and a (r) value of 0.1.