Journal Article

Continental Thermal Structure and Carbonate Storage of Subducted Sedimentary Origin Control on Different Increases in Atmospheric CO2 in Late Ediacaran and Jurassic

Wang, Xinxin, Yang, Jianfeng, Li, Jilei, Sun, Baolu, Chen, Ling, Zhao, Liang

2023

Overview

Carbon release during continental rifting is thought to regulate atmospheric CO2 levels. Supercontinent dispersal‐induced extensional tectonics is similar during the Late Ediacaran and Jurassic, while they exhibit different increases in atmospheric CO2 concentration. The underlying mechanism of distinct CO2 emissions remains to be understood. Here, we conduct petrological‐thermomechanical modeling to show that metamorphic decarbonation and melting of carbonates that are derived from subducted sediments are ubiquitous during continental extension. We find that the hotter lithosphere and deeper storage of these carbonates cause more significant amounts of rift‐related CO2 release through volcanoes and faults. They may cause ∼12%–77% larger decarbonation efficiency, providing an efficient driving mechanism for a ∼31% larger increase in atmospheric CO2 levels during the Late Ediacaran than throughout the Jurassic. The rapid eruption and deposition of recycled carbonatite volcanic ash may contribute to the production of Late Ediacaran marine carbonates with the largest negative δ13C (−12‰). Plain Language Summary The Late Ediacaran and Jurassic periods witnessed rapid increases in atmospheric CO2 concentration and significant negative carbon isotope excursions in marine carbonates during the Earth's history, but the dynamics of their changes remain enigmatic. In this study, we present high‐resolution petrological‐thermomechanical models of how these processes occur. Our results indicate that the extensional tectonics drives trans‐crustal faulting and thereby results in remobilized subcontinental lithospheric carbonates of subducted sedimentary origin (SLCSS) to melt and migrate upward along these faults. The efficiency of CO2 release from these carbonates via metamorphic reaction decarbonation is promoted by the deeper storage and hotter lithosphere, which can reach up to ∼12%–77% larger. Recycled carbonatite volcanic ash may rapidly erupt and deposit in shallow marine habitats following the emission of CO2 enriched in 13C, resulting in the formation of large negative δ13C in Late Ediacaran and Jurassic. We suggest that metamorphic CO2 degassing of remobilized subcontinental lithospheric mantle carbonates of subducted sedimentary origin (SLMCS) combined with a hotter lithosphere may be responsible for a 31% greater increase in atmospheric CO2 and the largest negative δ13C of −12‰ in the Late Ediacaran. Key Points Numerical modeling of decarbonation of subducted sedimentary carbonates during continental rifting Thermal structure of the continental lithosphere and carbon storage depth control the efficiency of CO2 degassing Decarbonation of stored sedimentary carbonates during continental rifting accounts for CO2 concentrations and negative δ13C in Late Ediacaran

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: atmospheric CO2 / Atmospheric models / Carbon 13 / Carbon dioxide / Carbon dioxide concentration / Carbon dioxide emissions / Carbon isotopes / Carbonates / CO2 degassing / Decarbonation / deep carbon cycle / Degassing / Earth mantle / Fault lines / Geological faults / Jurassic / Lithosphere / metamorphic decarbonation / numerical modeling / Plate tectonics / Rifting / sedimentary carbonate / Sediments / Storage / Subduction (geology) / Tectonics / Thermal structure / Thermomechanical analysis / Volcanic activity / Volcanic ash / Volcanoes