Shaping the Mantle: The Role of Superheated Core After Giant Impacts

TL;DR

This study tests whether a superheated core formed by a Moon-forming–scale giant impact can drive secondary mantle melting and basal melt layer (BML) formation by coupling Earth-sized SPH simulations with a parameterized mantle-melting model that uses core heat contents $Q_c$, mantle heat requirements $Q_m$, and a heat flux $F_c$ to regulate melting. Across a systematic suite of impacts, the authors find three plausible fates for the post-impact mantle: a fully molten mantle, a basal melt layer, or an early superplume, with rapid core-to-mantle heat transfer driving basal melting on timescales of hundreds to thousands of years and BML thicknesses of hundreds of kilometers. In the canonical Moon-forming scenario, the superheated core can induce partial remelting of the lower mantle within roughly $277$ to $5983$ years, forming a BML whose evolution may lead to a fully molten mantle or a long-lived basal magma ocean, depending on viscosity and subsequent dynamics. These results imply that primordial lower-mantle heterogeneity would be largely erased and have significant implications for Earth's long-term thermal evolution and geodynamo, with potential applicability to other terrestrial planets via similar core–mantle thermal resetting mechanisms.

Abstract

The Moon-forming giant impact significantly influenced the initial thermal state of Earth's mantle by generating a global magma ocean, marking the onset of mantle evolution. Recent Smoothed Particle Hydrodynamics (SPH) simulations indicate that such a collision would produce a superheated core, whose cooling would strongly influence subsequent mantle dynamics. Here, we present systematic SPH simulations of diverse giant-impact scenarios and show that the superheated core formed after the impact can trigger secondary mantle melting, thereby governing the final state of the magma ocean. To further quantify this effect, we employ a parameterized mantle-melting model to evaluate the influence of secondary melting on the lower mantle. Our results suggest three possible outcomes: complete mantle melting, the formation of a basal melt layer, or the initiation of an early superplume. Combined with recent two-phase magma-ocean solidification models, we infer that all three scenarios would result in basal melt layers of varying thickness, partially retaining the thermal energy of the superheated core. In the canonical Moon-forming scenario, the superheated core would rapidly transfer heat to Earth's lower mantle, causing secondary mantle melting within approximately 277-5983 years and generating either a basal melt layer or a fully molten mantle. Both outcomes would effectively erase primordial heterogeneities in the lower mantle and impose distinct pathways for its subsequent thermal evolution.

Figures (12)

• Figure 1: Schematic illustration of the parameterized mantle melting model. The left side shows the high-temperature core region, represented by red and yellow blocks, whereas the right side illustrates the cooler, solid mantle in green. Gray lines within the core denote the computational layers used to calculate internal heat transfer, each corresponding to a fixed temperature decrement along the core’s adiabatic profile at the core–mantle boundary (CMB). Black lines on the mantle side depict the progressive expansion of the basal mantle melting layer. The green line represents the rheological transition temperature, which was derived from the solidus and liquidus curves adopted in monteux2016. Markers 1 through 3 indicate different stages in the evolution of this melt layer, characterized by decreasing temperature and increasing thickness. Red arrows show the direction and progression of the upward and outward growth of the basal melting layer over time. This schematic conceptually links the core’s thermal structure to the dynamic melting response of the overlying mantle.
• Figure 2: Typical Giant Impact-Induced Mantle Melting States. This figure presents a cross-sectional view of three representative mantle melting states, as shown in Panels A, B, and C. The mantle particles are confined within a radial distance of $-0.1R_{\oplus} < R < 0.1R_{\oplus}$ along the Z-axis and projected onto the X–Y plane. Blue particles represent solid-phase material, while red particles indicate molten material or regions exceeding the melting temperature. The melting criterion is determined by Equations \ref{['equation17']}–\ref{['equation18']}.
• Figure 3: Thermal state of the proto-Earth following Moon-forming giant impacts. The top row shows results from the canonical impact model, while the bottom row corresponds to the sub-Earth impact model. In each row, the left panel presents a two-dimensional temperature distribution, with the color bar indicating temperature. The right panel displays the radial profile of mean temperature, where particles are color-coded according to their material origin: target core, target mantle, impactor core, and impactor mantle. Black lines indicate the average temperature profiles of the core and mantle. Impact parameters are listed in Supplementary Table \ref{['tab:summary']}, consistent with previous Moon-forming giant impact models canup2001origincanup2012forming.
• Figure 4: Melting of the solid lower mantle induced by a superheated core following the canonical impact. The left panel shows the post-impact mantle state, where the lower mantle remains solid. Simulation parameters are listed in Table \ref{['tab:symbols']}. The right panel illustrates the melting of the lower mantle driven by heat transfer from the superheated core. The horizontal axis denotes the melting timescale, and the vertical axis (BML radius) represents the distance from the core to the upper boundary of the basal melt layer (BML).
• Figure 5: Melting process of the lower mantle under the different viscosity assumption. Different colored lines represent different viscosities, resulting in varying melting times and melting behaviors.