Evidence for basalt enrichment in the mantle transition zone from inversion of triplicated P- and S-waveforms

Recycling of chemically stratified oceanic lithosphere at subduction zones and mantle mixing is the main source for production long-term maintenance heterogeneities as evidenced through samples presence seismic scatterers. The transition zone (MTZ), which bound by discontinuities around 410 660 km depth that reflect mineral phase transformations in olivine system, considered to play a significant role reprocessing remixing subducted plates. However, compositional nature state MTZ generally unconstrained with models ranging from fully-equilibrated pyrolitic mechanically-mixed enriched basalt. Here, we consider regional P- S-waveforms different regions have interacted extensively are triplicated discontinuities. Because strong interaction sensitivity temperature composition, waveforms can be used probes thermochemical conditions MTZ. model considering two-endmember models: mechanical mixture depleted (harzburgite) fertile (basalt) lithologies, whose properties computed self-consistently using petrologic equilibria combination equation-of-state modeling function pressure, temperature, composition. Based on this method, invert carefully selected local one-dimensional profiles structure. In some studied regions, find both radial lateral composition show trend more lithologies mid-MTZ compositions below This line evidence provided global geodynamic support segregation accumulation basalt toward mid-MTZ. number here encompass settings, also observe lower-than-average temperatures (∼1200∘C) and, consequence, thicker-than-average (∼240–280 km). While areas appear better fit particular model, rigorous statistical analysis datafit shows average, level resolving power data, an equilibrated across large part settings favored.