CO2-Rich Rejuvenated Stage Lavas on Hawaiian Islands

Abstract

Sedimentary carbonates are sent to the deep mantle if they are not completely destroyed at subduction zones, and subducted carbonates may contribute to plume volcanism. To better constrain the role of recycled carbonates in Hawaiian volcanism, we report high-precision olivine and whole-rock geochemical compositions of shield and rejuvenated stage lavas from Kauai, Oahu and Maui Islands. The studied rejuvenated stage whole-rocks have low SiO2 and high CaO concentrations, and are depleted in high field strength elements, such as, Nb and Zr, consistent with a role of carbonated melt. Rejuvenated stage olivines have Ni abundance lower than and CaO and MnO contents similar to those of shield stage at a given Fo. The calculated partition coefficients of Ca(Do1-meltCa) and Mn (Do1-meltMn) between olivine and shield melts are consistent with those of a dry melt system. However, the low Do1-meltCa and Do1-meltMn for rejuvenated lavas can only be explained by a volatile-rich melt system. Based on the observed Do1-meltCa and Do1-meltMn in rejuvenated lavas, and considering the effect of H2O, our modeling calculation shows that rejuvenated primary magmas contain up to ∼10 wt% CO2, indicating a CO2-rich mantle source. Using olivine-spinel aluminum exchange thermometry, we show that the rejuvenated primary magma temperatures are similar to those of shield stage. We posit that the CO2-rich rejuvenated stage lavas with lower olivine Ni than those of shield stage lavas were originated from melting of carbonated peridotites in the plume. The carbonated melts that metasomatized the peridotites were likely derived from subducted ancient carbonate-bearing lithospheric mantle.