Geochronology and geochemistry of Cadomian basement orthogneisses from the Tutak metamorphic Complex, Sanandaj-Sirjan Zone, Iran

A combined U-Pb geochronology, whole-rock geochemistry, and Sr-Nd isotopic study give new insights into the nature of the protolith, tectonic setting, and petrogenetic history of Cadomian orthogneisses from the Tutak metamorphic complex (TMC), Sanandaj-Sirjan Zone, Iran. U-Pb zircon dates of 535 +/- 4 Ma suggest an Early Cambrian crystallization age for the orthogneiss protoliths. Geochemical data indicate that the orthogneisses have I-type, high-K calc-alkaline, and peraluminous signatures. Depletion in Nb, Ta, Ti, Sr, and enrichment in Nd, Th, K, U relative to the primitive mantle, suggest derivation in a subduction zone environment in an active continental margin. Initial Sr-87/Sr-86 and Nd-143/Nd-144 ratios vary from 0.7045 to 0.7092 and from 0.5116 to 0.5117, respectively. Moreover, eNd( t) values range from -2.95 to -5.29, and two-stage model ages vary from 1.4 to 1.6 Ga. Taken together, these data suggest derivation of TMC orthogneisses from a metasomatic lithospheric mantle with a contribution of a crustal component generated via partial melting of a metabasite (i.e., amphibolite).

Automated summary

A study on Cadomian orthogneisses from the Tutak metamorphic complex in Iran reveals an Early Cambrian crystallization age and indicates derivation in a subduction zone environment. Isotopic data suggest a metasomatic lithospheric mantle source with a crustal component contributed via partial melting of metabasite.