An experimental study of peridotite dissolution in eclogite-derived melts: Implications for styles of melt-rock interaction in lithospheric mantle beneath the North China Craton

Interaction between eclogite-derived melt and peridotite has played an important role in modifying the cratonic lithospheric mantle and generation of high-Mg igneous rocks. To better understand the effect of peridotite physical state on melt-peridotite interaction, we conducted reaction experiments of lherzolite with two basaltic andesites and a ferro-basalt at temperatures of 1300 °C, 1375 °C, and 1425 °C and a pressure of 2 GPa using the reaction couple method. At 1300 °C, when lherzolite is subsolidus, its dissolution rate is slow, and it is mineralogically and texturally unchanged. Garnet and clinopyroxene precipitate at the melt-rock interface. The low-temperature reaction enriches the melt with SiO2 and Na2O, and depletes the melt with Al2O3, FeO, and CaO. At 1375 °C and 1425 °C, when the lherzolite is partially molten, the dissolution and re-equilibration rates are fast due to grain-scale process that involves dissolution, precipitation, and reprecipitation. Dissolution of olivine and precipitation of orthopyroxene produce a melt-bearing orthopyroxene-rich lithology at the melt-rock interface followed by a melt-bearing harzburgite and a melt-bearing lherzolite. The lithology near the interface can be an orthopyroxene-rich harzburgite or an orthopyroxenite depending on the reacting melt composition. The high-temperature reaction produces melt with increased MgO, FeO, CaO, and Mg#, and decreased SiO2, Al2O3, and Na2O. The dissolution rate obtained from the experiments is used to assess the survival of mantle xenoliths in the early Cretaceous high-Mg diorites. Combined with field observations from mantle samples, the experimental results provide insight into the style of eclogite-derived melt and peridotite interaction in the lithospheric mantle beneath the North China Craton. At the lithosphere-asthenosphere boundary, the reaction is dominated by the high-temperature regime, which produces orthopyroxene-rich lithologies such as orthopyroxene-rich harzburgite and orthopyroxenite-veined peridotite. Above the lithosphere-asthenosphere boundary where peridotite is subsolidus, the reaction is characterized by the low-temperature regime, which produces garnet-bearing or garnet-rich lithologies such as garnet pyroxenite, garnetite, and high-Mg granulite. Interactions between eclogite-derived melts and peridotite in the two regimes are responsible for the geochemical features of the early Cretaceous high-Mg igneous rocks from the North China Craton.