Geochronology and origin of the Elatia plutonite (Hellenic Rhodope Massif, N. Greece) constrained by new Sr isotopic data
Soldatos, T.; Koroneos, A.; Christofides, G.; Del Moro, A.
published: Jun 22, 2001
ArtNo. ESP154017602004, Price: 29.00 €
The Elatia plutonite constitutes the main part of the Elatia-Skaloti-Paranesti (ESP) granitic complex, which is the biggest of the Hellenic Rhodope Massif (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 coarse-grained (hornblende)-biotite granodiorite (GRD) with a marginal porphyritic phase. The GRD is intruded by dykes of fine- to medium-grained biotite granite to leucogranite (GR). The eastern part of the plutonite is occupied 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-bearing rocks (GRD) is about 4.6-6.3 kbar, while similar crystallization pressure - about 6 kbar - was estimated for the granites (GR-TMG). The GRD, GR and TMG comprise three distinct rock groups without any genetic relation among them. The age of the ESP complex should be considered 48 Ma at least or older. Although the whole-rock Rb-Sr errorchrons point to an Upper Cretaceous age, the 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 range between 43.5-47.8 Ma. Accordingly, the age of the TMG should be at least or not too much older than 48 Ma, this age being the younger limit for the 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 distribution 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 environment, most likely prior to the collision. Melting of amphibolitic or basaltic rocks under pressure of 8-16 kbar and temperature of 850-1100 °C could produce peraluminous or metaluminous melts similar to the initial GRD magma. Potential source rocks for GR are gneisses and rocks of tonalitic composition. Melts produced by dehydration melting of tonalitic rocks under temperature of 825-850 °C and pressure of 5-8 kbar are similar in composition to the GR rocks.