Plate tectonic degassing estimated from full-plate models and age distributions of arc-related zircons

Abstract

<p>Plate tectonics regulates atmospheric greenhouse gas concentrations and surface temperatures via sources (mainly volcanic CO<sub>2</sub> degassing) and sinks (silicate weathering and carbonate deposition). To constrain arc-volcanism, the main source of CO<sub>2</sub>, we argue that normalized subduction flux calculated from full-plate models is a reliable proxy, and notable peaks are observed during greenhouse conditions (e.g. the Early Cretaceous), whereas icehouse conditions are commonly characterized by reduced subduction flux (e.g. the Late Paleozoic Ice Age). The age distributions of arc-related zircons grossly mimic subduction fluxes and we present a new approach to estimate degassing through time by rescaling the global zircon age distribution to the subduction flux. Importantly, this approach permits estimation of plate tectonic degassing in deep time when full-plate models become increasingly unreliable. Full-plate models differ vividly before the assembly of Pangea, mainly due to different longitude-calibrations of continents and synthetic (“made-up”) oceanic realms, and variations in zircon-age-frequency allow us to estimate changes in volcanic arc-activity or plate tectonic degassing much more objectively in deep time. A first attempt to quantify volcanic arc-activity in deep time shows a pattern where low (high) degassing generally corresponds to periods of icehouse (greenhouse) for the past 3.5 billion years. We recognize a major shift in volcanic arc activity during the late Neoproterozoic (700-540 Ma) and this may reflect a transition to a modern-type plate tectonic regime with cold, deep and steep subduction.</p>