The Oligocene Avaj volcanic – plutonic complex of Central Iran: A record of magma evolution and mineral equilibria

The Avaj Oligocene volcanic – plutonic complex is part of extensive Cenozoic magmatic activity within the Urumieh-Dokhtar arc Iran. We use whole rock geochemistry, mineral compositions and crystal size distributions (CSD) in a suite co-genetic basalt, basaltic andesite gabbro to determine their petrogenesis. Ca-rich cores plagioclase (An79-86) overlap empirically modelled compositions, indicating equilibrium crystallization from melts represented by whole-rock compositions. Clinopyroxene (Mg# 74–80) are compatible with mildly fractionated mantle-derived magmas an setting. Mineral-melt inferred high Al contents close correspondence between measured DiHd predicted KdFe–Mg (0.23–0.32) clinopyroxenes, Kd(Plg/melt)(An–Ab) values (0.11–0.15). Clinopyroxene-melt thermometers indicate at 1119–1173 °C for 1099–1134 rocks. Plagioclase core saturation temperatures range 1088–1162 (volcanic) 1121–1163 (plutonic); these calculated mineral-melt temperatures. CSDs nearly straight both samples, higher nucleation density steeper slopes samples. Major element variations suggest rocks represent related fractional observed phases. minor crustal assimilation occurred during ascent deeper reservoir shallower one; CSD data longer magma residence time samples (∼117 years) compared (∼13 years).