Granitoids associated with East Vardar ophiolites (Serbia, F.Y.R. of Macedonia and northern Greece): Origin, evolution and geodynamic significance inferred from major and trace element data and Sr–Nd–Pb isotopes

Abstract

The paper presents and discusses a new set of major, trace and Sr–Nd–Pb data concerning Upper Jurassic granitoid rocks associated with the East Vardar ophiolites. These rocks form a discontinuous belt from Serbia in the north to northern Greece in the south. Two major styles of granitoid magmatism are recognized: (1) the southern granitoids form large intrusions cutting both the East Vardar ophiolites and the metamorphic rocks of the Serbo-Macedonian massif; (2) the northern granitoids are small petrogenetically variable bodies that are always spatially associated with ophiolites; these are probably multiphase, resulting in numerous low-volume granitoid intrusions within ophiolites. The southern granitoids (except at Fanos, N Greece) form an almost complete suite of decreasing radiogenic neodymium ( ɛ Nd( T) = 3.3 to − 8.9) and increasing radiogenic strontium (Sr i = 0.70740–0.71588) with increasing silica contents, and assimilation fractional crystallization (AFC) processes seem to have played an important role in their petrogenesis. Their primary magmas most probably originated by melting of a slightly enriched MORB-like mantle. The Fanos granite is a special case as it is characterized by a uniform isotopic composition for differently evolved rocks (Sr i = 0.70516–0.70559, ɛ Nd( T) = − 1.6 to − 0.7). This granite is interpreted to have derived from lower crustal melts that differentiated mainly through fractionation processes. The northern granitoid group consists of intermediate rocks (Sr i = 0.70557–0.70746, ɛ Nd( T) = − 4.5 to − 0.8), high-Sr i granites (Sr i = 0.70956–0.71602, ɛ Nd( T) = insertionofequalsignintheequationof(Nd(T)=−6to−5.1ifappropriate.-->− 6 to − 5.1, HREE- and Y-enriched) and low-Sr i granites (Sr i = 0.70330–0.70767, ɛ Nd( T) = − 5.1 to 1.5). High-Sr i granites are interpreted to have crystallized from peraluminous magmas generated by fusion of (meta)sedimentary rocks caused by obduction-induced melting. The northern intermediate rocks and the related low-Sr i granites have a wider range of composition and may be explained as genetically different rock groups. Some of them could have originated during obduction-induced melting of a source that was different from the source of high-Sr i granitoids, whereas others could be products of subduction-related volcanic arc magmatism.