Thermal effects of late accretion to the crust and mantle of Mercury

TL;DR

This study models the thermal impact of late accretion impacts on Mercury, showing that large impacts caused significant crustal melting and mantle heating, explaining observed volcanic regions and the erasure of ancient cratering.

Contribution

It introduces a 3D transient heating model to quantify impact-induced melting and mantle heating on Mercury during late accretion, linking impacts to volcanic and surface features.

Findings

Large impacts caused crustal melting and mantle heating.

Impact heating can produce high-magnesium melts matching observed volcanic regions.

Resurfacing and melting explain the erasure of ancient cratering record.

Abstract

Impact bombardment on Mercury in the solar system late accretion phase (ca. 4.4 to 3.8 Ga) caused considerable mechanical, chemical and thermal reworking of its silicate reservoirs (crust and mantle). Depending on the frequency, size and velocity of such impactors, effects included regional and global scale crustal melting, and thermal perturbations of the mercurian mantle. We use a 3D transient heating model to test the effects of two bombardment scenarios on early (pre Tolstojan) Mercury mantle and crust. Results show that rare impacts by the largest (greater than 100 km diameter) bodies deliver sufficient heat to the shallow mercurian mantle producing high-temperature ultra-magnesian (komatiitic s.s.) melts. Impact heating leading to effusive (flood) volcanism can account for eponymous High-Magnesium Region (HMR) observed during the MErcury Surface, Space Environment, GEochemistry Ranging (MESSENGER) mission. We find that late accretion to Mercury induced volumetrically significant crustal melting (less than 58 vol.percent), mantle heating and melt production, which, combined with extensive resurfacing (less than 100 percent), also explains why its oldest cratering record was effectively erased, consistent with crater-counting statistics.