Large igneous province degassing contributed to elevated atmospheric CO2 concentration in the Eocene

Deep carbon recycling plays a critical role in regulating Earth’s atmospheric CO2 and climate changes through time. However, the fate of subducted carbonate and potential driving factor of elevated atmospheric CO2 concentration in the Eocene are not well constrained. Here, we report Mg-Ca isotope of the Cenozoic (48 Ma) large igneous province (LIP) in the western Tianshan, to trace recycled marine carbonates in the deep mantle and evaluate the amount of magmatic degassed CO2. The basalts possess remarkably lighter δ26Mg and δ44/40Ca values than those of mantle, suggesting a source contributed by isotopically light recycled surficial carbonates. The quantitative modeling of Mg-Ca-Sr-Nd-Pb isotope reveals the Tianshan LIP magmatic CO2 degassing flux (~1.4–4.1 Pg/year) is two orders of magnitude higher than that of arc magmas. We highlight the subducted Neo-Tethyan oceanic lithosphere provided abundant recycled carbonates into mantle source of Tianshan LIP and induced high CO2 degassing fluxes, which contributed to elevated atmospheric CO2 during the Eocene. Acknowledgements: The present study was financially supported by Hong Kong Research Grant Council Joint Laboratory Funding Scheme (JLFS/P-701/18), NSFC Major Project (41890831) and Hong Kong RGC grants (17307918 and 17308023), and HKU Internal Grants for Member of Chinese Academy of Sciences (102009906) and Distinguished Research Achievement Award (102010100). This work is a contribution of the Joint Laboratory of Chemical Geodynamics between the University of Hong Kong and Guangzhou Institute of Geochemistry, Chinese Academy of Sciences.