Iranian Neo-Tethyan magmas as a significant CO2 source during the Middle Eocene Climatic Optimum

CO2 emissions from magmatic arcs can affect the atmosphere composition, thereby driving long-term global climate changes. Early Cenozoic climate trends are generally associated with changes in global silicate weathering related to Neo-Tethyan geodynamics, but the likely climatic effects of changes in degassing from Neo-Tethyan magmatic arcs have been poorly quantified. Here, we characterize the petrography and provide the first measures of the volatile content (CO2, H2O, F, Cl, and S) of pre-eruptive melts based on glassy, bubble-bearing and reheated melt inclusions within plagioclase and clinopyroxene crystals in Early Cenozoic trachyandesites from the Alborz and Tabriz regions (Iran). CO2 concentrations in these melt inclusions reach up to 6733 ppm, thus providing a minimum estimate of the total amount of CO2 degassed from Iranian magmas during the middle-late Eocene of 1.01 × 1019 (± 4.04 × 1017) g CO2, with a total C flux released of 0.306 (± 0.012) Mt. C/yr, which is within the carbon imbalance predictions estimated based on other proxies. Our measures validate earlier hypotheses that magmatic CO2 degassing from the targeted igneous provinces contributed to the Middle Eocene Climatic Optimum. Further measurements of the volatiles content of Neo-Tethyan magmas are thus critical to assess the drivers of Early Cenozoic climate trends and understand the global volatile cycling over geological timescales.