Subduction fluxes through geologic time

Much of my research career has been spent working both on modern oceanic volcanic systems and at the same time looking at their Archaean counterparts. Many authors have attempted to make inferences on early Earth models based on modern processes which can be increasingly well constrained. In this short review I show how we are beginning to understand and quantify inputs to modern subduction systems and I pose some questions as to how these processes may have affected Earth’s evolution in its distant past. Geochemical models have convincingly demonstrated that sediment and altered oceanic crust must be recycled into the mantle through subduction zones. These ‘subduction factories’ use these components, along with molten mantle, to create arc magmas. The ‘residue’ from this process is recycled into the mantle and has a modified chemical and mineralogical composition. The altered oceanic crust input function in the current plate tectonic cycle seems to be relatively constant in composition, but the chemical compositions of the sediment fluxes into subduction zones vary widely and control many of the end-member compositions of arc magmas. They must also control the compositions of fluids and gases derived from these magmas and ultimately ore-deposition and atmospheric fluxes associated with arc volcanoes. There is relatively strong evidence for subduction processes for at least the past 3.5 Ma and some would argue that exogenic components have been recycled into the mantle since at least ~4.3 Ma. How might the subduction fluxes have changed through time, and how might they have influenced crust, ocean and atmospheric compositions? Can different ore regimes in temporal and spatial distribution on Earth be related to the change in inputs and residues from the subduction factory through time?