Compositional characteristics and geodynamic significance of late Miocene volcanic rocks associated with the Chah Zard epithermal gold–silver deposit, southwest Yazd, Iran
Kouhestani, H and Ghaderi, M and Emami, MH and Meffre, S and Kamenetsky, V and McPhie, J and Zaw, K and Bezenjani, RN, Compositional characteristics and geodynamic significance of late Miocene volcanic rocks associated with the Chah Zard epithermal gold-silver deposit, southwest Yazd, Iran, Island Arc, 27, (1) Article e12223. ISSN 1038-4871 (2018) [Refereed Article]
Whole-rock geochemical and Sr–Nd isotopic data are presented for late Miocene volcanic rocks associated with the Chah Zard epithermal Au–Ag deposit in the Urumieh-Dokhtar Magmatic Arc (UDMA), Iran, to investigate the magma source, petrogenesis and the geodynamic evolution of the study area. The Chah Zard andesitic to rhyolitic volcanic rocks are characterized by significant Large Ion Lithophile Element (LILE) and Light Rare Earth Element (LREE) enrichment coupled with High Field Strength Element (HFSE) depletion. Our geochemical data indicate an adakitic-like signature for the volcanic rocks (e.g. SiO2 > 62 wt%, Al2O3 > 15 wt%, MgO < 1.5 wt%, Sr/Y > 70, La/Yb > 35, Yb < 1 ppm, and Y < 18 ppm, and no significant Eu anomalies), distinguishing them from the other volcanic rocks of the UDMA. The Chah Zard volcanic rocks have similar Sr and Nd isotopic compositions; the 87Sr/86Sr(i) ratios range from 0.704 902 to 0.705 093 and the εNd(i) values are from +2.33 to +2.70. However, the rhyolite porphyry represents the final stage of magmatism in the area and has a relatively high 87Sr/86Sr ratio (0.705 811). Our data suggest that the andesitic magmas are from a heterogeneous source and likely to result from partial melting of a metasomatized mantle wedge associated with a mixture of subducted oceanic crust and sediment. These melts subsequently underwent fractional crystallization along with minor amounts of crustal assimilation. Our study is consistent with the model that the volcanic host rocks to epithermal gold mineralization in the UDMA are genetically related to late Miocene Neo-Tethyan slab break-off beneath Central Iran.