Magmatic evolution of the migrating central Urumieh–Dokhtar arc, Iran: implications for magma production
Résumé
The Cenozoic Avaj volcano-plutonic rocks in central Urumieh-Dokhtar magmatic arc (UDMA) encompass gabbro, and basalt to rhyolite, chemically akin to those from continental arcs. U–Pb geochronology on zircon yielded ages of 23.69 ± 0.48 Ma, 24.71 ± 0.38 Ma, 20.92 ± 0.14 Ma, and 19.25 ± 0.13 Ma for gabbro, basalt, trachyandesite, and rhyolite, respectively. εHf(t) values for zircon grains are ranging from − 1.4 to + 6.2. The data display narrow ranges of initial Pb isotopic ratios and εNd(t) values, implying a fairly homogeneous source. Moderate 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, high 143Nd/144Nd ratios of the mafic samples highlight the role of mantle components. The isotopic ratios–incompatible trace elements modelings reveal ~ 2% of the melt come from the melting sediments in the petrogenesis of Avaj igneous rocks. The central UDMA with ages ranging from 42–38 Ma and 25–18 Ma, respectively, must have experienced two relatively brief periods of important magma production separated by ~ 14–15 M.y. The early period of magma production correlates with the Middle Eocene Climatic Optimum (MECO), while the second magmatic period of the central UDMA is not associated with increasing CO2 contents in the atmosphere. The plutons of the older group are generally located to the east of those from the younger group suggesting a SW-directed migration of the arc following slab rollback. No systematic change of source compositions and magma formation is observed between the older and younger rocks implying similar magma sources and subduction input from the Eocene to Miocene. The potential effect of the UDMA magmatic activity on the global climate apparently does not reflect decreasing subduction of carbonate.