Mid-Cretaceous extensional magmatism in the Alborz Mountains, north Iran; geochemistry and geochronology of Gasht-Masuleh gabbros

Abstract In the Gasht-Masuleh area in Alborz Mountains, gabbroic magma intruded Palaeozoic metasediments and Mesozoic sediments crystallised as isotropic cumulate gabbros. LREE enrichment points to relatively low degrees of mantle melting depletion Ti, Nb Ta relative primitive an arc related component magma. Clinopyroxene compositions indicate MORB signatures. U–Pb zircon crystallisation ages 99.5 ± 0.6 Ma 99.4 phlogopite 40 Ar/ 39 Ar 97.1 0.4 Ma, 97.5 0.1 within 2σ error, that gabbro intrusion occurred (Albian-)Cenomanian (mid-Cretaceous). As active subduction did not take place Cretaceous North Iran, small volume mafic magmatism must be due local, extension-related melting. Melting was most likely caused by far field effects triggered roll-back Neo-Tethys subducting slab. took at a distance ~ 400 km (present distance) from observed geochemical signatures inherited previous event concomitant metasomatism, possibly combination with contamination crustal material.