Petrology and geochemistry of Nabijan gabbroic and dioritic plutons (south west Kaleybar, NW Iran): an implication for post-collision magmatism

The Nabijan gabbroic and dioritic plutons outcropped at the southwest Kaleybar town. According to the field studies the diorite is younger than gabbro and crosscut the gabbroic pluton. Geochemical data reveal clear geochemical difference between the Nabijan gabbroic and dioritic compositions. Variations of major oxides versus SiO2 and Mg# and trace element ratios indicate that the composition of Nabijan intrusive bodies were modified by fractional crystallization and crustal contamination (AFC) processes. However the geochemical characteristics of the Nabijan plutons suggest a same source for them. According to mineralogical and geochemical data¡ fractionation and/ or accumulation of olivine¡ orthopyroxene¡ clinopyroxene and Ca-rich plagioclase at the first stage has formed the gabbroic body. Due to fractionation of the above mentioned minerals¡ the composition of the remained magma has enriched by fluids and incompatible elements. At the final stage the Nabijan diorites has formed by crystallization of amphibole¡ biotite¡ Na-rich plagioclase accompanied with minor amounts of clinopyroxene. The fractionation/accumulation of the mentioned mineral associations has caused to possess tholeiitic and calc-alkaline character for the Nabijan gabbroic and diorites¡ respectively. The geochemical features of the Nabijan intrusive rocks show hybrid characteristics among active continental margin and within plate tectonic settings. These features can visible in continental post-collision settings.