Early crustal processes revealed by the ejection site of the oldest martian meteorite

Abstract

The formation and differentiation of the crust of Mars in the first tens of millions of years after its accretion can only be deciphered from incredibly limited records. The martian breccia NWA 7034 and its paired stones is one of them. This meteorite contains the oldest martian igneous material ever dated: ~4.5 Ga old. However, its source and geological context have so far remained unknown. Here, we show that the meteorite was ejected 5-10 Ma ago from the north-east of the Terra Cimmeria-Sirenum province, in the southern hemisphere of Mars. More specifically, the breccia belongs to the ejecta deposits of the Khujirt crater formed 1.5 Ga ago, and it was ejected as a result of the formation of the Karratha crater 5-10 Ma ago. Our findings demonstrate that the Terra Cimmeria-Sirenum province is a relic of the differentiated primordial martian crust, formed shortly after the accretion of the planet, and that it constitutes a unique record of early crustal processes. This province is an ideal landing site for future missions aiming to unravel the first tens of millions of years of the history of Mars and, by extension, of all terrestrial planets, including the Earth.

Fig. 1. Summary of NWA 7034 and paired stone radiometric ages, and chronology of major events experienced by the breccia.

Dates from each study are reported in Supplementary Data 1. The ejection event is constrained from ²²Ne/²¹Ne cosmic ray exposure ages^, . Whole rock (w.r), zircon and or baddeleyite (zr.b), apatite (ap), and augite (aug) on which ages have measured are also mentioned. The different chronometers used in these studies are reported (Sm-Nd, Pb-Pb, U-Pb, K-Ar, U-Th/He, U-Th-Sm/He). Note that green, red and blue boxes correspond to resetting ages of the noted chronometer. Reset ages in green are widely interpreted as the disruption induced by an impact-derived heating event that has excavated the oldest components of the breccia ~1.5 ago^{, , ,} , although its precise age is still unconstrained due to the wide range of isotopic dates reported in the literature.

Fig. 2. Distribution of the most likely crater sources for martian meteorites.

a Global context of the 19 crater candidates (Supplementary Table 1) and location of provinces and rovers (yellow triangles) referred to in the present study. Background: Mars Orbiter Laser Altimeter (MOLA) shaded relief (https://astrogeology.usgs.gov/search/map/Mars/GlobalSurveyor/MOLA/Mars_MGS_MOLA_DEM_mosaic_global_463m). b, c: Magnetic field intensity and remanent magnetization at the surface from ref. . d, e Potassium and Thorium concentration at the surface from ref. ^,. Beige area corresponds to discarded provinces due to the weathered basaltic surface contribution (Methods).

Fig. 3. The NWA 7034 launch site geological context.

a Perspective view (Context Camera mosaic) and cross-section through Karratha along a SW-NE axis (Supplementary Fig. 5b) as interpreted from numerical modelling simulations. Shades of colors denote impactites (impact melt and in situ breccia; ejecta and fall-back breccia). b Schematic of chronological events experienced by the host terrain of the regolith breccia.