The role of crustal recycling: Coevolution of deep-mantle structure and geochemical heterogeneity

The life-cycle of an oceanic plate begins with melting and ends with subduction. These two processes constitute the primary means by which mantle heterogeneity is created and destroyed. Though the extent of their influence is obscured by the limitations of physical experiments (reproducing mantle conditions down the core remains intractable) and for empirical reasons (nonunique interpretations of the data). In trying to address these challenges, we examine the influence of crustal recycling using geodynamic models that cover a range of physical parameters, and test their fit to two major datasets: the mantle isotope array and global seismic tomography. Our models include an explicitly evolving isotopic composition that accounts for the production of enriched basalt and depleted harzburgite at spreading ridges, the recycling of those components at subduction zones and a contribution from continental sediment. The temperature and composition fields are then used to predict variations in seismic wavespeed where the uneven and incomplete resolution of tomographic model, S40RTS, is accounted for. We find that models that best explain the mantle isotope array also provide the best fit to lowermost mantle structure imaged by S40RTS.