Discussion on the Eocene bimodal Piranshahr massif of the Sanadaj–Sirjan Zone, West Iran: a marker of the end of collision in the Zagros orogen

Abstract

Mazhari et al . (2009) provide valuable geochemical and geochronological data for plutonic rocks from the Piranshar massif. This is one of a set of plutons within the Sanandaj–Sirjan zone in Iran, SW of the Urumieh–Dokhtar magmatic zone. This comment is not about the new data of Mazhari et al . (2009), but refers to their interpretation that the c . 41 Ma (Middle Eocene) intrusions in the Piranshahr massif post-date the initial collision of the Arabian and Eurasian plates by 10–20 Ma. I argue that (1) these magmatic rocks are not reliable markers of a tectonic setting post-dating initial collision, and (2) there are abundant geological data that suggest initial collision was later, most plausibly in the Late Eocene ( c . 35 Ma). The main argument presented for a tectonic setting post-dating initial collision is the A2-type chemistry of the felsic rocks within the massif. By comparison with other A2-type granitoids reviewed by Eby (1990, 1992) it is concluded that the intrusions were emplaced some 10–20 Ma after initial collision (i.e. Palaeocene to Early Eocene, …