Original paper

The Almogholagh pluton, Sanandaj-Sirjan zone, Iran: geochemistry, U-(Th)-Pb titanite geochronology and implications for its tectonic evolution

Shahbazi, H.; Siebel, W.; Ghorbani, M.; Pourmoafee, M.; Sepahi, A. A.; Abedini, M. Vousoughi; Shang, C. K.


Subduction related granitoids, generated during northward motion of Arabia and subduction of the Neo-Tethys ocean under the southern margin of Eurasia, are found in the Sanandaj–Sirjan zone, western Iran. The Almogholagh pluton (∼200 km2), located in the northern Sanandaj-Sirjan zone, is thought to have formed along this convergent plate boundary at some time between the late Mesozoic and early Cenozoic. The pluton is intrusive into the Triassic-Jurassic Hamedan phyllites. Here we present geochemical, Sr–Nd isotopic and U-(Th)-Pb titanite data for monzonitic rocks of this complex. The rocks are metaluminous and belong to the low-K calc-alkaline magma series. Silica-rich samples exhibit an affinity to A-type granites as testified by their high Zr, Nb, Ce, Y and low Ba and Sr concentrations. Field investigation, petrography and U-(Th)-Pb titanite dating demonstrate that the Almogholagh pluton emplaced syntectonically during regional deformation between late Jurassic and early Cretaceous times. Subsequently, parts of the pluton, along brittle-ductile shear zones, were metamorphosed under lower greenschist-facies conditions. Monzonites and monzodiorites of the Almogholagh pluton are characterized by low initial 87Sr/86Sr (0.7045, 0.7058) and positive εNd(t) values (2.7, 2.8). These features are in line with derivation by partial melting of mafic rocks in the lower crust. The overall tectonic regime was characterized by melt formation, ascent and emplacement along an active continental margin of the Sanandaj-Sirjan zone during a period of arc extension.


arc magmatismalmogholagh plutonsanandaj-sirjan zonetitanite datingsr-nd isotopes