Remobilization of carbon in the lithospheric mantle during decratonization

Abstract

The sub-continental lithosphere mantle (SCLM) contains considerable amounts of carbon and is responsible for significant CO2 emissions via magmatism during major heating and rifting events. However, the role of SCLM in Earth's carbon cycle during other geological processes, such as decratonization, a process of major removal and replacement of cratonic SCLM, remains poorly understood. The North China Craton is an archetype of Archean craton having been decratonized during the Mesozoic with extensive magmatism developed. Here we show that the primary melt of Early Cretaceous Yixian basalts contained abundant CO2 (0.6 wt%), through investigating melt inclusions trapped in olivine crystals. The melt inclusions are alkalic and chemically distinct from their sub-alkalic host basalts, which could be explained by that the primary alkalic melt was reactively modified during magma ascent in the SCLM. The primary melt has geochemical characteristics consistent with partial melting of a veined carbon-rich amphibole clinopyroxenite source in the SCLM formed metasomatically during circum-craton subduction events. The findings highlight that the carbon introduced into the cratonic SCLM during subduction could be subsequently reactivated and transferred to the crust and atmosphere through decratonization-related magmatism, which might represent a major process regarding the SCLM in regulating the terrestrial carbon cycle.