The role of continental arc magmatism in driving long-term climate change

Abstract:

Earth’s long-term climate states – icehouses and greenhouses – are largely governed by shifts in the concentration of atmospheric CO_2. Silicate weathering and the burial of organic matter are primary sinks for CO₂ and metamorphic and volcanic degassing are the primary sources. Continental magmatic arcs, in particular, have the ability produce large CO₂ fluxes by liberating C preserved in continental bedrock. Assessment of a large compilation of detrital zircon U-Pb age data demonstrates systematic shifts in global zircon production that correspond with major shifts in icehouse–greenhouse climates: zircon generation is highest during greenhouses and lowest during icehouses. As zircon is predominantly produced in felsic melts in continental arc systems, these data demonstrate a first-order relationship between spatiotemporal variation in continental magmatism and major transitions in climate state. Since no clear consistent relationship can be discerned between long-term climate shifts and the paleogeographic location of continents or the global extent of uplift with regard to silicate weathering, it appears that the volcanic CO₂ flux exerts a dominant control on shifts in baseline climate. The most prominent lulls in arc magmatism coincide with dramatic glaciations (e.g, Proterozoic Snowball Earth events), whereas extensive global volcanism and magmatic flare-ups correspond with intervals of documented environmental stress and mass extinctions, illustrating the fundamental influence of plate tectonic processes on Earth’s surface environment and the evolution of the biosphere. In addition, the carbon cycle model LOSCAR is used to quantify the potential leverage of varying volcanic CO₂ flux on equilibrium atmospheric CO₂ under varying strengths and formulations of the silicate weathering feedback, which demonstrates the importance of the volcanic flux on baseline atmospheric CO₂.