Geochemistry and Tectonic Setting of Western Avaj Gabbros, Northwest of Iran

The western Avaj intrusive bodies, composed mainly of gabbroic rocks, have intruded into low grade regional metamorphic rocks of Razan Subzone and formed small and elongated plutons. The gabbroic rocks in the marginal part of intrusions deformed during emplacement and show mylonitic texture. The foliation in the marginal mylonitic gabbro is parallel to the foliation of host metamorphic rocks with NW-SE direction. A narrow low grade metamorphic aureole was formed around these intrusions. Petrologic relationships and the origin of the different intrusive outcrops are demonstrated by petrography and geochemical studies. Geochemical signatures on spider diagram indicate that the role of fractional crystallization on the magma evolution was more important than the contamination or partial melting. Trace element pattern on the spider diagrams suggests an extensional regime for tectonic setting of the gabbroic rocks. Seemingly, these rocks were possibly generated by partial melting of an enriched lithospheric mantle source (EM) in depth of about 50 to 60 kilometers.