The Tharsis mantle source of depleted shergottites revealed by 90 million impact craters

A Lagain,K Servis,E K Sansom,H A R Devillepoix,A Rajšic,L S Doucet,M C Towner,K Miljković,P A Bland,G K Benedix,D Baratoux

doi:10.1038/s41467-021-26648-3

Abstract

The only martian rock samples on Earth are meteorites ejected from the surface of Mars by asteroid impacts. The locations and geological contexts of the launch sites are currently unknown. Determining the impact locations is essential to unravel the relations between the evolution of the martian interior and its surface. Here we adapt a Crater Detection Algorithm that compile a database of 90 million impact craters, allowing to determine the potential launch position of these meteorites through the observation of secondary crater fields. We show that Tooting and 09-000015 craters, both located in the Tharsis volcanic province, are the most likely source of the depleted shergottites ejected 1.1 million year ago. This implies that a major thermal anomaly deeply rooted in the mantle under Tharsis was active over most of the geological history of the planet, and has sampled a depleted mantle, that has retained until recently geochemical signatures of Mars’ early history.

Highlights

The only martian rock samples on Earth are meteorites ejected from the surface of Mars by asteroid impacts
Considering that olivine phenocrysts in the ol-phyric depleted shergottites are in near-equilibrium with their parental melt, the potential mantle temperature (Tp) can be estimated from 1714 to 1835 °C28,29
On Earth, the broad range of potential mantle temperatures reflects the diversity of mantle melting environment, such as hot spots or large igneous provinces above mantle plume, mid-oceanic ridges or fluid-enhanced melting at subduction zones

Summary

Introduction

The only martian rock samples on Earth are meteorites ejected from the surface of Mars by asteroid impacts. It would be possible that a rock sampled at a given place by a meteoritic impact had been previously transported by other processes (such as a previous impact with no evidence of shock), we will assume here that the rocks were generated at the impact location by magmatic processes This group includes basaltic and poikilitic textures but is largely dominated by olivine-phyric shergottites and is characterized by a common depletion in REE. The variability of crystallization ages and peak shock pressures reported for this group of depleted shergottites launched 1.1 Myr ago[4] imply that a wide diversity of volcanic rocks was ejected from different geological units exposed at the surface of Mars or at shallow depths. Numerical simulations suggest that impact events capable of producing such fragments would form craters larger than ~3 km in diameter on the Martian surface[9,10]

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Results

Conclusion