Distinct sources for high-K and adakitic magmatism in SE Iran

Abstract

Research into Arabia-Eurasia collision zone magmatism in Kerman Province, SE Iran, has largely focused on Late Cenozoic adakitic stocks or domes, with debate around lower crustal or subducted slab origins. Contemporary hawaiite-trachyandesite lava flows have been overlooked. New analyses for domes and lavas from near Dehaj show major and trace element distributions relating to two distinct compositional series. One contains medium-K domes with SiO2 > 60 wt%, high Sr/Y and La/Yb and generally low MgO, Ni and Cr, showing high-silica adakite affinity. The other series has high-K affinity and includes both lavas and dome samples. The two suites partially mixed in the shallow crust, confirmed by fieldwork and petrography. Isotopically the two suites are indistinguishable, implying a geologically ‘young’ age for the source of the adakites. Given its geochemical signatures and non-relationship with the more mafic, mantle-derived high-K series, we consider the adakite series to be derived from melting of eclogitized mafic lower crust. The high-K series relates to dehydration melting of mantle deeper within the ~220 km thick lithosphere. We also explore adakitic magmas across Iran and their relationship to porphyry copper deposits. At Dehaj and several other Iranian centres, adakites are chemically controlled by garnet as a source or fractionating phase, and are barren, whereas the presence of amphibole as a key phase seems to correlate with Cu mineralisation. This study also shows the need for evidence from multiple datasets to constrain adakite genesis and warns of avoiding sampling bias towards felsic lithologies.