Ocean Basalt Simulator version 1 (OBS1): Trace element mass balance in adiabatic melting of a pyroxenite-bearing peridotite

Abstract:

We present a new numerical mass balance model for estimating the source conditions of a primary ocean basalt from adiabatic melting of a pyroxenite-bearing peridotite. The Ocean Basalt Simulator version 1 (OBS1) uses a thermodynamic model of adiabatic melting of a pyroxenite-bearing peridotite with experimentally parameterized liquidus–solidus and melting intervals and thermodynamically/experimentally parameterized source mineralogy of pyroxenite and peridotite. OBS1 uses a sequence of adiabatic melting with pyroxenite melting, melt metasomatism in the host peridotite, and melting of the metasomatized peridotite. OBS1 explores (1) the fractions of peridotite and pyroxenite, (2) mantle potential temperature T_p, (3) depth of termination of melting P_mt, (4) degree of melting F, and (5) residual mode Xa of the sources. The model also examines the mass balance of 26 incompatible trace elements in the sources and in the generated basalt. OBS1 can also calculate Sr–Nd–Hf–Pb isotope compositions in the sources and in the melt. OBS1 is coded in an Excel spreadsheet and runs with VBA macros. Using OBS1, we examine the source conditions of the mid oceanic ridge basalts (MORBs), plume-influenced ocean ridge basalts in Galápagos, Loihi–Loa–Koolau basalts in the Hawaiian hotspot, high-mu (HIMU) basalt from the St. Helena hotspot, and Shatsky Rise and Jurassic Mikabu oceanic plateau basalts and picrites. OBS1 is a unique model that provides an opportunity to examine the source mantle conditions using incompatible trace elements and relevant isotopes, which are key factors in global mantle recycling.