On the iron isotope composition of Mars and volatile depletion in the terrestrial planets

Iron is the most abundant multivalent element in planetary reservoirs, meaning its isotope composition (expressed as δ57Fe) may record signatures of processes that occurred during the formation and subsequent differentiation of the terrestrial planets. Chondritic meteorites, putative constituents of the planets and remnants of undifferentiated inner solar system bodies, have δ57Fe ≈ 0‰; an isotopic signature shared with the Martian Shergottite–Nakhlite–Chassignite (SNC) suite of meteorites. The silicate Earth and Moon, as represented by basaltic rocks, are distinctly heavier, δ57Fe≈+0.1‰. However, some authors have recently argued, on the basis of iron isotope measurements of abyssal peridotites, that the composition of the Earth’s mantle is δ57Fe = +0.04 ± 0.04‰, indistinguishable from the mean Martian value. To provide a more robust estimate for Mars, we present new high-precision iron isotope data on 17 SNC meteorites and 5 mineral separates. We find that the iron isotope compositions of Martian meteorites reflect igneous processes, with nakhlites and evolved shergottites displaying heavier δ57Fe(+0.05 ± 0.03‰), whereas MgO-rich rocks are lighter (δ57Fe≈−0.01 ±0.02‰). These systematics are controlled by the fractionation of olivine and pyroxene, attested to by the lighter isotope composition of pyroxene compared to whole rock nakhlites. Extrapolation of the δ57Fe SNC liquid line of descent to a putative Martian mantle yields a δ57Fe value lighter than its terrestrial counterpart, but indistinguishable from chondrites. Iron isotopes in planetary basalts of the inner solar system correlate positively with Fe/Mn and silicon isotopes. While Mars and IV-Vesta are undepleted in iron and accordingly have chondritic δ57Fe, the Earth experienced volatile depletion at low (1300 K) temperatures, likely at an early stage in the solar nebula, whereas additional post-nebular Fe loss is possible for the Moon and angrites

What Martian Meteorites Reveal About the Interior and Surface of Mars

Martian meteorites are the only direct samples from Mars, thus far. Currently, there are a total of 262 individual samples originating from at least 11 ejection events. Geochemical analyses, through techniques that are also used on terrestrial rocks, provide fundamental insights into the bulk composition, differentiation and evolution, mantle heterogeneity, and role of secondary processes, such as aqueous alteration and shock, on Mars. Martian meteorites display a wide range in mineralogy and chemistry, but are predominantly basaltic in composition. Over the past 6 years, the number of martian meteorites recovered has almost doubled allowing for studies that evaluate these meteorites as suites of igneous rocks. However, the martian meteorites represent a biased sampling of the surface of Mars with unknown ejection locations. The geology of Mars cannot be unraveled solely by analyzing these meteorites. Rocks analyzed by rovers on the surface of Mars are of distinct composition to the meteorites, highlighting the importance of Mars missions, especially sample return. The Mars 2020 Perseverance rover will collect and cache—for eventual return to Earth—over 30 diverse surface samples from Jezero crater. These returned samples will allow for Earth‐based state‐of‐the‐art analyses on diverse martian rocks with known field context. The complementary study of returned samples and meteorites will help to constrain the evolution of the martian interior and surface. Here, we review recent findings and advances in the study of martian meteorites and examine how returned samples would complement and enhance our knowledge of Mars

Mesoproterozoic reworking of palaeoproterozoic ultrahigh-temperature granulites in the Central Indian Tectonic Zone and its implications

In the southern periphery of the Sausar Mobile Belt (SMB), the southern component of the Central Indian Tectonic Zone (CITZ), a suite of felsic and aluminous granulites, intruded by gabbro, noritic gabbro, norite and orthopyroxenite, records the polymetamorphic evolution of the CITZ. Using sequences of prograde, peak and retrograde reaction textures, mineral chemistry, geothermobarometric results and petrogenetic grid considerations from the felsic and the aluminous granulites and applying metamorphosed mafic dyke markers and geochronological constraints, two temporally unrelated granulite-facies tectonothermal events of Pre-Grenvillian age have been established. The first event caused Ultrahigh-temperature (UHT) metamorphism (M1) (T ∼950°C) at relatively deeper crustal levels (P ∼9 kbar) and a subsequent post-peak near-isobaric cooling P–T history (M2). M1 caused pervasive biotite-dehydration melting, producing garnet–orthopyroxene and garnet–rutile and sapphirine–spinel-bearing incongruent solid assemblages in felsic and aluminous granulites, respectively. During M2, garnet–corundum and later spinel–sillimanite–biotite assemblages were produced by reacting sapphirine–spinel–sillimanite and rehydration of garnet–corundum assemblages, respectively. Applying Electron Microprobe (EMP) dating techniques to monazites included in M1 garnet or occurring in low-strain domains in the felsic granulites, the UHT metamorphism is dated at 2040–2090 Ma. Based on the deep crustal heating–cooling P–T trajectory, the authors infer an overall counterclockwise P–T path for this UHT event. During the second granulite event, the Palaeoproterozoic granulites experienced crustal attenuation to ∼6•4 kbar at T ∼675°C during M3 and subsequent near-isothermal loading to ∼8 kbar during M4. In the felsic granulites, the former is marked by decomposition of M1 garnet to orthopyroxene–plagioclase symplectites. During M4, there was renewed growth of garnet–quartz symplectites in the felsic granulites, replacing the M3 mineral assemblage and also the appearance of coronal garnet–quartz–clinopyroxene assemblages in metamorphosed mafic dykes. Using monazites from metamorphic overgrowths and metamorphic recrystallization domains from the felsic granulite, the M4 metamorphism is dated at 1525–1450 Ma. Using geochronological and metamorphic constraints, the authors interpret the M3–M4 stages to be part of the same Mesoproterozoic tectonothermal event. The result provides the first documentation of UHT metamorphism and Palaeo- and Mesoproterozoic metamorphic processes in the CITZ. On a broader scale, the findings are also consistent with the current prediction that isobarically cooled granulites require a separate orogeny for their exhumation

Consolidated Chemical Provinces on Mars: Implications for Geologic Interpretations

International audienceChemical provinces were defined on Mars a decade ago using orbital nuclear spectroscopy of K, Th, Fe, Si, Ca, Cl, and H2O. However, past multivariate analyses yielded three sets of provinces, suggesting methodologic variability. Province-stability to the inclusion of Al and S is also unknown, presenting additional uncertainties for geologic insight. Here we consolidate key multivariate methods to define the first cross-validated provinces. In southern highlands, the highly incompatible K and Th show non-uniform distribution with higher values in mid Noachian and Hesperian than late Noachian – early Hesperian volcanic terrains. Silica- and Al-depletion trends from Noachian to Amazonian indicate highly differentiated mantle with variable degree of melting. Late Hesperian lowlands are highly depleted in Al and enriched in K and Th, consistent with volcanic resurfacing from a low-degree partially melted, garnet-rich mantle. Furthermore, older volatile-rich regions such as Medusae Fossae Formation exhibit igneous geochemistry, consistent with water-limited isochemical weathering throughout Mars's history

2001 Mars Odyssey Gamma Ray Spectrometer Element Concentration Maps

Chemical provinces were defined on Mars a decade ago using orbital nuclear spectroscopy of K, Th, Fe, Si, Ca, Cl, and H2O. However, past multivariate analyses yielded three sets of provinces, suggesting methodologic variability. Province-stability to the inclusion of Al and S is also unknown, presenting additional uncertainties for geologic insight. Here we consolidate key multivariate methods to define the first cross-validated provinces. In southern highlands, the highly incompatible K and Th show non-uniform distribution with higher values in mid Noachian and Hesperian than late Noachian – early Hesperian volcanic terrains. Silica- and Al-depletion trends from Noachian to Amazonian indicate highly differentiated mantle with variable degree of melting. Late Hesperian lowlands are highly depleted in Al and enriched in K and Th, consistent with volcanic resurfacing from a low-degree partially melted, garnet-rich mantle. Furthermore, older volatile-rich regions such as Medusae Fossae Formation exhibit igneous geochemistry, consistent with water-limited isochemical weathering throughout Mars\u27s history

Boulder fall activity in the Jezero crater, Mars

International audienceJezero crater is the landing site for the Mars 2020 Perseverance rover. We report 63 boulder fall tracks within the crater using High Resolution Imaging Science Experiment (HiRISE) images. The boulder tracks have both fresh and faded morphologies similar to those reported elsewhere on Mars, but reported for the first time in Jezero crater. We combine observations from 16 boulder‐tracks on the western delta deposit with 47 in the surrounding regions to infer possible process (es) of boulder destabilization, which can be tested with rover observations. This newly‐found hazard should be taken into account for rover operations. Boulders associated with tracks are geologically “recent falls”, so it is possible that the surfaces of these boulders may provide an opportunity to sample material less exposed to radiation than other rocks at the martian surface and could be ideal targets to analyze for organics