Uranium-series disequilibria in MORB, revisited: A systematic numerical approach to partial melting of a heterogeneous mantle

We present computational modeling outcomes for bilithologic (peridotite and pyroxenite) mantle melting in divergent environments, considering equilibrium and disequilibrium porous flow melting of 0-50 % pyroxenite in thermal equilibrium with peridotite, potential temperatures of 1300 and 1400 degrees C, upwelling rates from 1-50 cm yr(-1), maximum porosities of 0.1-2.0 %, and four compositions that span pyroxenite melting behavior. Basalt-like pyroxenites (G2) uniquely produce low (Ra-226/Th-230) and (Pa-231/U-235) with high (Th-230/U-238), but quantities greater than similar to 10 % produce anomalously thick crust, restricting their global abundance. Silica-deficient pyroxenite (M7-16 and MIX1G) melts are more moderate, but require chemical re-equilibration during transport to resemble global basalts, while hybrid lithologies (KG1) produce melts similar to those of peridotites. Uranium-series disequilibria in partial melts can also be decoupled from trace elements by radioactive decay in two-dimensional regimes. The mantle must thus contain multiple types of pyroxenite on a global scale, with melts traveling by complex networks and experiencing heterogeneous extents of chemical re-equilibration.