Abstract

Two calc-alkaline plutonic complexes. Bazman and Natanz, intruded through the south-eastern active and south-western ancient continental margins of Central Iran, Have been dated by the Rb-Sr whole-rock isochron method at 74 ± 2 and 24 ± 4.5 Ma, respectively. Detailed trace element studies together with low 87Sr/86Sr initial ratios (<0.706) indicate that these complexes represent parts of an Andean-type magmatic are formed in response to subduction of Tethyan oceanic crust beneath Central Iran. Geochemical data on the igneous rocks at Bazman suggest that subduction of the Oman oceanic crust was well established by the late Cretaceous. On the evidence of the Natanz rocks, the Arabian-Central Iranian collision did not occur during the late Cretaceous, but took place during late Paleogene or early Neogene time. The Natanz low-Rb diorites and gabbros cannot be comagmatic with the more salic rocks, for they have distinctly lower 87Sr/86Sr ratios and the gabbros, at least, were intruded some 10 Ma earlier.

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