Geochronology and origin of the Elatia plutonite (Hellenic Rhodope Massif,N. Greece) constrained by new Sr isotopic data

The Elatia plutonite constitutes the main part of the Elatia-Skaloti-Parane sti (ESP) granitic complex, which is the biggest of the Hellenic Rhodope Ma ssif (HRM) in northern Greece. It intrudes the metamorphic basement of the upper tectonic unit (UTU) of the HRM. Its main lithology is a medium- to co arse-grained (hornblende)-biotite granodiorite (GRD) with a marginal porphy ritic phase. The GRD is intruded by dykes of fine- to medium-grained biotit e granite to leucogranite (GR). The eastern part of the plutonite is occupi ed by a two-mica granite (TMG), which intrudes the GRD. The rocks have typical calc-alkaline character and they are metaluminous to peraluminous. The calculated crystallization pressure of the hornblende-be aring rocks (GRD) is about 4.6-6.3 kbar, while similar crystallization pres sure - about 6 kbar was estimated for the granites (GR-TMG). The GRD, GR an d TMG comprise three distinct rock groups without any genetic relation amon g them. The age of the ESP complex should be considered 48 Ma at least or older. Al though the whole-rock Rb-Sr errorchrons point to an Upper Cretaceous age, t he Rb-Sr biotite ages range between 34.1-43.0 Ma in GRD and between 36.9-42 .0 Ma in GR. In TMG the biotite age is 39.4 Ma, while the muscovite ages ra nge between 43.5-47.8 Ma. Accordingly, the age of the TMG should be at leas t or not too much older than 48 Ma, this age being the younger limit for th e GRD, which must be older than 48 Ma. Consequently, the plutonic magmatism in the UTU of the HRM is considerably older (Eocene or older) than that in the rest of the HRM (Oligocene-Miocene). The southwestward decrease of the Rb-Sr biotite ages could be attributed to the thrust between the upper and lower tectonic units of the HRM, which most probably happened at about 34 Ma ago. Alternatively, a "layered tilted" pluton could explain the distribu tion of the mica ages. Any metamorphic event affected the western HRM must be older than 50 Ma. The Elatia plutonite magma genesis is related to a subduction tectonic envi ronment, most likely prior to the collision. Melting of amphibolitic or bas altic rocks under pressure of 8-16 kbar and temperature of 850-1100 degrees C could produce peraluminous or metaluminous melts similar to the initial G RD magma. Potential source rocks for GR are gneisses and rocks of tonalitic composition. Melts produced by dehydration melting of tonalitic rocks unde r temperature of 825-850 degreesC and pressure of 5-8 kbar are similar in c omposition to the GR rocks.