فاطمه سرجوقیان

All samples exhibit high Sr (av: 1227 ppm), low Y (av: 13.44 ppm) and Yb (av: 1.28 ppm) contents and high Sr/Y (av: 108.37) and La/Yb (av: 22.18), jointly indicate that the studied intrusion can be classified as adakitic rocks. However, other typical features of adakites are high Na2O contents (3.5–7.5 wt.%) and low K2O/Na2O ratio (<0.42), which clearly contrast with the K-rich compositions of the studeid intrusive complex (av: K2O/Na2O: 1.11). The following evidence indicates that these basalts do not resulted by AFC processes. Coexisting mafic rocks within the studeid intrusive complex occur in very small volumes, and it is unlikely that fractionation of such small volumes of mafic magmas could be responsible for the large volumes of granitoid rocks. Their Sr/Y and La/Yb ratios have no obvious correlations with MgO and SiO2, suggesting that high Sr/Y and La/Yb ratios were inherited from a source region rather than produced by magma differentiation. The low Rb/Sr ratios (av: 0.12) rule out an origin from a mafic magma by extensive fractional crystallization. Also, higher 87Sr/86Sr and lower 143Nd/144Nd relative to adakites from mantle, and lower 87Sr/86Sr and higher 143Nd/144Nd relative to adakites from lower crust melting suggesting the studied intrusion were proposed to have originated from partial melting of the delaminated lower continental crust (LCC), followed by interaction with the mantle peridotites.ctional crystallization and reflecting a partial melting model. We conclude that delamination could also explain the thinning of the Eocene crust in this part of Central Iran, as a consequence of sinking of eclogitic material from the base of the lithosphere into the underlying mantle. Therefore lithospheric thinning and delamination of thickened continental crust were responsible for the petrogenesis of the studied adakitic rocks