Petrological characterization of the Cenozoic igneous rocks of the Tafresh area, central Urumieh-Dokhtar Magmatic Arc (Iran)

We report a petrographic and whole-rock geochemical characterization of the Cenozoic igneous rocks cropping out in the Tafresh area, central Urumieh-Dokhtar Magmatic Arc, NW Iran. The investigated rocks range mainly from basaltic andesite to dacite, and are considered to be genetically linked to a three-step, (mostly) closed-system evolutionary process. It involves first the fractionation of ferromagnesian minerals (mainly clinopyroxene and olivine) and plagioclase, followed by a second removal of plagioclase and lesser amphibole (plus minor clinopyroxene) and eventually, in the most evolved phases, the crystallization of plagioclase with lesser alkali feldspar and minor amphibole. Tafresh rocks define a typical calcalkaline series generated from a subduction-modified mantle wedge, characterized by the classical LILE-enriched and HFSE-depleted compositions. The basaltic andesite magmas do not represent primitive compositions, but are likely derived from an unsampled hydrous primitive melt equilibrated in a spinel-bearing metasomatized peridotite source, evolving at shallow to moderate crustal depths. Additional lithotypes cropping out in the Tafresh area include much rarer strongly evolved leucocratic rocks and evolved rocks with adakitic signature. The first are thought to derive from crustal anatexis of a meta-sedimentary source, whereas the latter are interpreted as the product of the melting of a meta-mafic source rock with residual garnet and amphibole. The association of magmatic rocks pointing to all such different petrogenetic processes in a relatively limited area is strongly suggestive of emplacement in a post-collisional stage.