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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 °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 (226Ra/230Th) and (231Pa/235U) with high (230Th/238U), but quantities greater than ~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. 

Data set of faults from southern Vietnam 

One mafic whole rock lava sample was dated using 40Ar/39Ar geochronology to determine the maximum age of faulting in the area, based on the observation that the lava flow is cross-cut by a fault. 

40Ar/39Ar isotope data measured from the groundmass of six mafic and one intermediate whole rock lava sample from south-central Vietnam to determine their eruption ages. 

We present data for lithospheric mantle xenoliths sampled from two alkali basalts in south‐central Vietnam, Pleiku and Xuan Loc, including fertile spinel peridotites. To better determine the origins of the Indochinese subcontinental lithospheric mantle (SCLM), including impacts of posited tectonic extrusion, we present major and trace elements, and 87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb in xenolith mineral separates. Most peridotites from Pleiku and Xuan Loc have fertile major element compositions, “depleted” and “spoon‐shaped” rare earth element (REE) patterns, interpreted to record prior melt depletion followed by melt metasomatism, and variable but generally depleted isotopic signatures (e.g., 87Sr/86Sr = 0.70238–0.70337 and 143Nd/144Nd = 0.512921–0.514190). A small group of refractory peridotites have “enriched” REE patterns suggesting more extensive metasomatism and enriched isotope ratios (87Sr/86Sr = 0.70405 and 143Nd/144Nd = 0.512755–0.512800). The presence of both fertile and refractory xenoliths records a heterogeneous SCLM beneath Vietnam. Based on geothermobarometry calculations, fertile xenoliths have equilibrium temperatures of 923–1,034°C and pressures of 11.7–15.8 kbar, while refractory xenoliths have comparable temperatures of 923–1,006°C, but lower pressures of 7.1–10.0 kbar, suggesting refractory rocks are dominantly present at shallower depths. We suggest that the lithospheric mantle has experienced variable melt extraction around 1.0–1.3 Ga, producing heterogeneous major element compositions. While we cannot rule out partial removal and replacement of the lithosphere, large‐scale delamination is not necessary to explain observed characteristics. The entire SCLM was more recently metasomatized by melts resembling Cenozoic basalts, suggesting recent asthenospheric melting has modified the SCLM by melt infiltration. 

Radiogenic isotopes (Sr-Nd-Pb-Hf) as well as major and trace elements were measured in whole-rock lava samples from south-central Vietnam. 

Radiogenic isotope data measured in lithospheric mantle xenolith whole rocks from south-central Vietnam. Samples are peridotite xenoliths from two alkali basalt locations in Vietnam, Pleiku and Xuan Loc. Data are radiogenic isotopes measured by TIMS and MC-ICP-MS in clinopyroxene mineral separates. 

Major element data measured by electron probe analysis in crystal separates for lithospheric mantle xenoliths from south-central Vietnam. Samples are peridotite xenoliths from two alkali basalt locations in Vietnam, Pleiku and Xuan Loc. Data are major elements measured by EPMA in mineral separates. 

Trace element data measured by LA-ICP-MS analysis in crystal separates for lithospheric mantle xenoliths from south-central Vietnam. Samples are peridotite xenoliths from two alkali basalt locations in Vietnam, Pleiku and Xuan Loc. Data are trace elements measured by LA-ICP-MS in mineral separates.