Trace element and bulk chemistry of plumes and ridges in geodynamic simulations

Volumetrically, the most important magmatic source on Earth is beneath mid-ocean ridges, from which mid-ocean ridge basalts (MORBs) are sourced. Second to this is plume related magmatism, the source for ocean-island basalts (OIBs). Decades of geochemical analysis have discerned that MORBs exhibit low isotopic variation, which is interpreted to mean that their source is globally homogeneous at an ocean basin (and possibly global) scale. OIBs, however, exhibit strong isotopic variation not just spatially, but even temporally, indicating a compositionally heterogenous source region. Global scale numerical geodynamic models, driven by reconstructed plate motions, generate both plume and ridge structures at which melting occurs, similar to Earth, however it is not known how well dynamic models can re-create the first-order observation that ridge lavas are typically homogenous compared to plume lavas.

Using the 3D spherical mantle convection code, TERRA, constrained by plate motion reconstructions spanning 1Gyr of Earth’s history, ridge and plume structures are simultaneously generated. The location of ridges is known from the input plate reconstruction model, while plumes are identified using the simulated temperature and radial velocity fields and a combination of K-means and density-based clustering. Using our approach, we can not only compare the properties of ridges and plumes, but can also compare the properties of ridges across different ocean basins and of individual simulated mantle plumes. Analysis of the bulk composition and melting age of tracer particles associated with ridges and plumes allows us to better interpret the history of material found in these regions. We analyse the U ratio to see if recent (~600 Ma) changes in the subducted U flux are evident in differences in the U composition of plume and ridge material.