RELATIVE INVOLVEMENT OF MANTLE AND CRUSTAL COMPONENTS IN THE AGACORENGRANITOID (CENTRAL ANATOLIA, TURKEY) - ESTIMATES FROM TRACE-ELEMENT AND SR-ISOTOPE DATA

Trace element contents, together with Sr-isotope ratios on a limited n umber of samples, are reported for the central part of the Agacoren gr anitoid in central Anatolia (Turkey), Trace element contents are depic ted in terms of Ocean Ridge Granitoid (ORG)-normalized elemental patte rns. The patterns display similarities to Volcanic Arc Granitoids (VAG ) and/or Collision Granitoids (COLG), and are characterized by enrichm ent in Large Ion Lithophile (LIL) elements relative to High Field Stre ngth (HFS) elements, negative Ba and positive Rb, Th and Ce anomalies, and high Th/Nb ratios. A comparison with the patterns typical of uppe r continental crust, lower continental crust and volcanic are calc-alk aline basalt implies that the Agacoren granitoid inherited its pattern essentially from the upper crust, although inheritance-in part-from a subduction modified upper mantle is also possible. Plot of Rb/Sr rati os against the initial Sr-87/Sr-86 ratios at the time of granitoid int rusion (110 Ma) suggests the derivation of granitoid from a mixture of about 70% (upper) crustal + 30% mantle components, the mixture later undergoing a maximum of about 21% fractional crystallization. The rela tive proportion of mantle and crustal components, as constrained from the isotope data, exceeds the limits-for complete hybridization-impose d by mechanical and thermal arguments, but falls into the range for co mmingling (incomplete mixing) of mafic and felsic magmas, the validity of which is also supported by the presence of mafic microgranular enc laves in the granitoid. The modeling of trace element data based on th e estimates from isotope data yield elemental patterns generally confo rmable to those displayed by granitic samples.