Revistes Catalanes amb Accés Obert (RACO)

The spatial and compositional evolution of the Late Jurassic Ghorveh-Dehgolan plutons of the Zagros Orogen, Iran: SHRIMP zircon U-Pb and Sr and Nd isotope evidence

S. Yajam, P. Montero, J.H. Scarrow, J. Ghalamghash, S.M.H Razavi, F. Bea

Resum


The Ghorveh-Dehgolan plutons of the northern Sanandaj-Sirjan Zone, Zagros Orogen, comprise seven composite intrusive bodies that were generated during northeastward subduction of Neotethys beneath the Iranian sector of the Eurasian plate. Zircon U-Pb SHRIMP dating reveals that the magmatic activity spanned from ~160 to ~140Ma. It started with intrusion of arc-related calc-alkaline mafic to intermediate rocks closely followed by felsic I-type granitoids. This magmatism was post-dated by felsic alkaline A-type granites. In addition to compositional changes over time, the plutons forming the arc young towards the southwest: the north Ghorveh batholith (161 ± 4Ma) and Shanevareh (160 ± 2Ma); Qalaylan (159 ± 3Ma); then central Ghorveh, Galali and Saranjianeh (151 ± 0.2Ma to 148± 1Ma); and, lastly, the south Ghorveh batholith (147 ± 3Ma) and Bolbanabad-Havarpan (144 ± 1Ma). Whatever the process driving the changes, be it arc- or ridge-collision with the subducting system, slab roll-back, slab break-off, subduction initiation transference, etc., the progression from I-type to A-type magmatism appears to mark a significant change from a collisional to an extensional setting in the region in the Late Jurassic. Geochemical and isotopic characteristics of the Ghorveh-Dehgolan plutons indicate that Arabian-Nubian-like crust was an important component of the magmatic sources.

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