The Magma Chamber Simulator (MCS) is a thermodynamic tool for modeling the evolution of magmatic systems that are open with respect to assimilation of partial melts or stoped blocks, magma recharge + mixing, and fractional crystallization. MCS is available for both PC and Mac. In the MCS, the thermal, mass, and compositional evolution of a multicomponentmultiphase composite system of resident magma, wallrock, and recharge reservoirs is tracked by rigorous self-consistent thermodynamic modeling. A Recharge-Assimilation (Assimilated partial melt or Stoped blocks)-Fractional Crystallization (R n AS n FC; n tot ≤ 30) scenario is computed by minimization or maximization of appropriate thermodynamic potentials using the family of rhyolite-and pMELTS engines coupled to an Excel Visual Basic interface. In MCS, during isobaric cooling and crystallization, resident magma thermally interacts with wallrock that is in internal thermodynamic equilibrium. Wallrock partial melt above a user-defined percolation threshold is homogenized (i.e., brought in to chemical potential equilibrium) with resident magma. Crystals that form become part of a cumulate reservoir that remains thermally connected but chemically isolated from resident melt. Up to 30 instances (n ≤ 30) of magma mixing by recharge and/or bulk assimilation of stoped wallrock blocks can occur in a single simulation; each recharge magma or stoped block has a unique user-defined composition and thermal state. Recharge magmas and stoped blocks hybridize (equilibrate) with resident melt, yielding a single new melt composition and temperature. MCS output includes major and trace element concentrations and isotopic ratios (Sr, Nd, Hf, Pb, Os, and O as defaults) of wallrock, recharge magma/stoped blocks, resident magma melt, and cumulates. The chemical formulae of equilibrium crystalline phases in the cumulate reservoir, wallrock, and recharge magmas/stoped blocks are also output. Depending on the selected rhyolite-MELTS engine, the composition and properties of a possible supercritical fluid phase (H 2 O and/or CO 2 ) are also tracked. Forward modeling of theoretical magma systems and suites of igneous rocks provides quantitative insight into key questions in igneous petrology such as mantle versus crustal contributions to terrestrial magmas, the record of magmatism preserved in cumulates and exsolved fluids, and the chronology of RASFC processes that may be recorded by crystal populations, melt inclusions, and whole rocks. Here, we describe the design of the MCS software that focuses on major element compositions and phase equilibria (MCS-PhaseEQ). Case studies that involve fractional crystallization, magma recharge + mixing, and crustal contamination of a depleted basalt that resides in average upper crust illustrate the major element and phase equilibria consequences of these processes and highlight the rich array of data produced by MCS. The cases presented here, which represent an infinitesimal fraction of possible RASFC processes and bulk compositions, show that the rec...

We examine the fractional crystallization of intermediate depth (~160-260 km), impact-induced magma oceans on Mars, and find that residual liquids become denser than normal Martian mantle. Fractional crystallization near 3 GPa establishes inverted density distributions that can generate melt descent within the mantle. Liquid compositions produced by~45-80 wt% crystallization become dense enough to descend to the core-mantle boundary and could form a stably stratified thermochemical boundary layer (TCBL). If this layer crystallizes, its mineralogy would be dominated by either garnet and ferropericlase or stishovite and ringwoodite. Although the size of Mars' core remains uncertain, the addition of such a thermal boundary layer would impede stabilization of (Mg, Fe)SiO 3 -perovskite at the base of the mantle. A TCBL would both elevate the inferred temperature of the core and inhibit heat flow out of the core, with a potentially causal relation with the current lack of an internally generated Martian magnetic field. Plain Language SummaryWe modeled the crystallization of magma oceans on Mars that reach depths of a few hundred kilometers. As the magma ocean crystallizes, the residual liquids become denser than the crystallizing minerals and solid mantle material. The liquids can become dense enough to sink to the base of Mars' mantle and form a chemically distinct layer around the core. This layer would raise the inferred temperature of the core and reduce heat flow out of the core, which could potentially explain the current lack of an internally generated Martian magnetic field.

A comprehensive analysis of experimental data and theoretical simulations on the partial molar volume of water in silicate melt indicates that finite strain theory successfully describes the compression of the H2O component dissolved in silicate melt at high pressures and temperatures. However, because of the high compressibility of the water component, a fourth order equation of state fit is required to accurately simulate experimental results on water's volume in silicate melts at a deep upper mantle, transition zone, and lower mantle pressures. Data from previous shock compression experiments on hydrous minerals in which melting occurs along the Hugoniot are used to provide an experimental constraint on the partial molar volume of water in silicate melt at deep mantle temperatures and pressures. The equation of state of the water component indicates that, depending on elastic averaging technique, the amount of water that could be present in neutrally or negatively buoyant mafic/ultramafic melts above the 410 km seismic discontinuity is upper‐bounded at 5.6 wt%: smaller than previously inferred, and consistent with melt being confined to a narrow depth range above the 410 km discontinuity. If melt is predominantly distributed along grain boundaries in low aspect ratio films, extents of melting as low as 2% could produce observed seismic velocity reductions. The ability of the lowermost mantle to contain negatively buoyant hydrous liquids hinges on the trade‐off between iron content and hydration: at these depths, substantially higher degrees of hydration could be present within partial melts.

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