Enstatite chondrites are a small clan of meteorites, only ~ 1% out of all meteorite collection. However, they are the most reduced meteorites and have almost identical isotopic compositions to those ...of the Earth, suggestive of significant contributions to the latter and other terrestrial planets. Enstatite chondrites contain a unique mineral inventory of sulfides of typical lithophile elements, Si-bearing metal, silicide and phosphide, which record the nebular processes and the thermal metamorphism in asteroidal bodies under extremely reducing environments. EH group is mainly characteristic of the higher Si content of metallic Fe–Ni and the higher MnS contents of sulfides than EL group, indicative of a more reducing condition than the latter. However, the fugacity p
H2S
could be the same in both EH and EL regions, because it was buffered by kamacite and troilite. The majority of sulfides condensed from the nebula, partially enclosing schreibersite micron-spherules formed probably by early melting. Another part of troilite, sphalerite and djerfisherite, intergrown with perryite, were produced via sulfidation of metallic Fe–Ni. Minor exotic components were also found in enstatite chondrites, including Ca-, Al-rich inclusions and FeO-rich silicate clasts. The Ca-, Al-rich inclusions are identical to those in carbonaceous chondrites except for the alteration under reducing environments, and the FeO-rich silicate clasts show reduction reactions, both suggestive of migration of dust in the protoplanetary disk. The highly reducing conditions (as C/O ratios) might be established via repeating evaporation and condensation of water ice and organic matter across the snow line along the protoplanetary disk, but need to find evidence. Another issue is the preservation of submicron-to-micron-sized presolar grains during high-temperature condensation of the major constituent minerals. After accretion, the parent bodies of EH and EL chondrites probably experienced distinct thermal histories, indicated by their distinct petrologic-type distributions and different correlations with the closure temperatures determined by the FeS contents of sulfides in contact with troilite.
The composition of (Mg, Mn, Fe)S, a key indicator for condensation and metamorphism of enstatite chondrites.
The Moon has a magmatic and thermal history that is distinct from that of the terrestrial planets
. Radioisotope dating of lunar samples suggests that most lunar basaltic magmatism ceased by around ...2.9-2.8 billion years ago (Ga)
, although younger basalts between 3 Ga and 1 Ga have been suggested by crater-counting chronology, which has large uncertainties owing to the lack of returned samples for calibration
. Here we report a precise lead-lead age of 2,030 ± 4 million years ago for basalt clasts returned by the Chang'e-5 mission, and a
U/
Pb ratio (µ value)
of about 680 for a source that evolved through two stages of differentiation. This is the youngest crystallization age reported so far for lunar basalts by radiometric dating, extending the duration of lunar volcanism by approximately 800-900 million years. The µ value of the Chang'e-5 basalt mantle source is within the range of low-titanium and high-titanium basalts from Apollo sites (µ value of about 300-1,000), but notably lower than those of potassium, rare-earth elements and phosphorus (KREEP) and high-aluminium basalts
(µ value of about 2,600-3,700), indicating that the Chang'e-5 basalts were produced by melting of a KREEP-poor source. This age provides a pivotal calibration point for crater-counting chronology in the inner Solar System and provides insight on the volcanic and thermal history of the Moon.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
Micrometeorite impacts and solar wind irradiation, the dominant space weathering (SW) processes, largely modified compositions and microtexture of soil materials on the Moon. Here, we report the SW ...characteristics of the Chang'e‐5 lunar soils from mid‐high latitude (43.06°N). All mineral phases exposed on the surface of a single basalt clast have a vapor deposit layer, whereas the textures of the solar wind irradiation‐damaged zone are dependent on the host mineral species. Nanophase Fe (npFe0) particles are spherical in the amorphized zone of pyroxenes, elongated in ilmenite, and irregular on the jagged surface of iron sulfide, but not found in Fe‐poor merrillite. Vesicles were found in the damaged zone of ilmenite and merrillite, but with different shapes. The observations were compared to Apollo samples and demonstrate no significant altitude‐dependent effects on the SW, which is important for decoding the reflectance spectra of the Moon.
Plain Language Summary
The lunar surface has been suffering intense meteorite impacts and solar wind irradiation for billions of years, which heavily modifies its physical properties, chemical compositions and mineralogical features, and in turn, the optical reflectance spectra of the Moon. The meteorite impacts are random events, but the intensity of solar wind irradiation is latitude dependent. However, all Apollo and Luna missions landed in a narrow and low range of lunar latitude. The Chang'e‐5 (CE‐5) mission returned lunar soil samples from a middle latitude (43.06°N), providing unique samples for study of lunar space weathering (SW). In this paper, we report the SW features of various minerals from a single basaltic clast of the CE‐5 sample. Our observations reveal phase‐dependent effects on the SW. Furthermore, the CE‐5 lunar soil shows no significant differences from those of Apollo samples, suggestive of little latitude‐dependent effects on lunar SW.
Key Points
The space weathering (SW) characteristics of lunar soils returned by Chang'e‐5 landing at the mid‐high latitude site are reported
Microscopic textures of SW depend on mineral species but show no relationship with the latitude of sampling site
The SW products by micrometeorite impacts and solar wind irradiation are distinguished
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
This study focuses on using the chemical compositions of plagioclase to further investigate the petrogenesis of Chang'E-5 young mare basalts and constrain its parental melt composition. Together with ...previously published data, our results show that the plagioclase in mare basalts overall displays large variations in major and trace element concentrations. Inversion of the plagioclase data indicates that the melt compositions parental to Chang'E-5 basalts have high rare earth elements (REE) concentrations similar to the high-K KREEP rocks (potassium, rare earth elements, and phosphorus). Such a signature is unlikely to result from the assimilation of KREEP components, because the estimated melt Sr shows positive correlations with other trace elements (e.g., Ba, La), which are far from the KREEP end-member. Instead, the nearly parallel REE distributions and a high degree of trace element enrichment in plagioclase indicate an extensive fractional crystallization process. Furthermore, the estimated melt REE concentrations from plagioclase are slightly higher than those from clinopyroxene, consistent with its relatively later crystallization. Using the Ti partition coefficient between plagioclase and melt, we estimated the parental melt TiO2 content from the earliest crystallized plagioclase to be ∼3.3 ± 0.4 wt%, thus providing robust evidence for a low-Ti and non-KREEP origin for the Chang'E-5 young basalts in the Procellarum KREEP terrane.
Lunar paleoregolith was formed by repeated asteroid impact and space weathering and then buried by later lava flows, serving as important records for early solar system history. However, direct ...observational evidence for the paleoregolith layer is rather limited. We present the evidence for the existence of the paleoregolith layer by processing 60 MHz lunar penetrating radar data acquired by the Chang’E‐3 Yutu rover. We find successive reflections with reversed polarities due to a low permittivity (paleoregolith) layer sandwiched in two high permittivity (lava) layers. From modeling and migration imaging of radar reflections, we determine an ultra‐thick paleoregolith layer (∼5–9 m) beneath the Eratosthenian unit and on the top of the Imbrian unit, suggesting a high regolith production rate of 5.8–10.5 m/Ga between late Imbrian and early Eratosthenian periods compared to the previous estimation ∼2 m/Ga, implying fast regolith formation and possible high meteoric flux during these periods.
Plain Language Summary
The surface of the Moon experienced multiple volcano eruptions since its birth and the large basin was filled with dark lava flows. Within this period due to repeated asteroid impact and space weathering between lava flows, the paleoregolith layers will be likely formed and buried by younger lava flows. The paleoregolith layers have been undisturbed since their formation thus are critical for determining early impacting and volcano history of the Moon and are regarded as important records for uncovering early Moon's history and early solar system history. We present the evidence for the existence of the paleoregolith layer in the northern Mare Imbrium basin by processing 60 MHz lunar penetrating radar data acquired by the Chang’E‐3 Yutu rover. From modeling and migration imaging of radar reflections, we determine an ultra‐thick paleoregolith layer (∼5–9 m) beneath the Eratosthenian unit and on the top of the Imbrian unit, implying fast regolith formation and possible high meteoric flux during these periods.
Key Points
Successive reflections with reversed polarities due to a low permittivity layer sandwiched in two high permittivity layers
An ultra‐thick paleoregolith layer (∼5–9 m) beneath Eratosthenian unit and on the top of Imbrian unit
A high regolith production rate of 5.8–10.5 m/Ga between late Imbrian and early Eratosthenian periods compared to previous estimate ∼2 m/Ga
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The distribution of water in the Moon's interior carries implications for the origin of the Moon
, the crystallization of the lunar magma ocean
and the duration of lunar volcanism
. The Chang'e-5 ...mission returned some of the youngest mare basalt samples reported so far, dated at 2.0 billion years ago (Ga)
, from the northwestern Procellarum KREEP Terrane, providing a probe into the spatiotemporal evolution of lunar water. Here we report the water abundances and hydrogen isotope compositions of apatite and ilmenite-hosted melt inclusions from the Chang'e-5 basalts. We derive a maximum water abundance of 283 ± 22 μg g
and a deuterium/hydrogen ratio of (1.06 ± 0.25) × 10
for the parent magma. Accounting for low-degree partial melting of the depleted mantle followed by extensive magma fractional crystallization
, we estimate a maximum mantle water abundance of 1-5 μg g
, suggesting that the Moon's youngest volcanism was not driven by abundant water in its mantle source. Such a modest water content for the Chang'e-5 basalt mantle source region is at the low end of the range estimated from mare basalts that erupted from around 4.0 Ga to 2.8 Ga (refs.
), suggesting that the mantle source of the Chang'e-5 basalts had become dehydrated by 2.0 Ga through previous melt extraction from the Procellarum KREEP Terrane mantle during prolonged volcanic activity.
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Volcanic history of the Imbrium basin Zhang, Jinhai; Yang, Wei; Hu, Sen ...
Proceedings of the National Academy of Sciences - PNAS,
04/2015, Volume:
112, Issue:
17
Journal Article
Peer reviewed
Open access
We report the surface exploration by the lunar rover Yutu that landed on the young lava flow in the northeastern part of the Mare Imbrium, which is the largest basin on the nearside of the Moon and ...is filled with several basalt units estimated to date from 3.5 to 2.0 Ga. The onboard lunar penetrating radar conducted a 114-m-long profile, which measured a thickness of ∼5 m of the lunar regolith layer and detected three underlying basalt units at depths of 195, 215, and 345 m. The radar measurements suggest underestimation of the global lunar regolith thickness by other methods and reveal a vast volume of the last volcano eruption. The in situ spectral reflectance and elemental analysis of the lunar soil at the landing site suggest that the young basalt could be derived from an ilmenite- rich mantle reservoir and then assimilated by 10–20% of the last residual melt of the lunar magma ocean.
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Akimotoite (Mg,Fe)SiO3-ilmenite was encountered in shock-induced melt veins of Grove Mountains (GRV) 052082, a highly equilibrated low iron ordinary chondritic meteorite (L6). Coexistence of ...ringwoodite, majorite, and majorite-pyrope solid solution indicates the shock pressure at 18-23 GPa and temperature of 2000-2300 °C during the natural dynamic event. Most low-Ca pyroxene clasts entrained in the melt veins have been partially or entirely transformed into akimotoite-pyroxene glass assemblages, which contain micrometer-sized areas with various brightness in the backscattered electron images, different from the chemically homogeneous grains in the host-rock (Fs20.5-21.3). The transmission electron microscopy study of a focused ion beam (FIB) slice from the heterogeneous areas shows that the assemblages are composed of FeO-depleted and heterogeneous akimotoite (Fs6-19) crystals (100 nm up to 400 nm in size) scattered in FeO-enriched and relatively homogeneous pyroxene glass (Fs31-39). All analyses of the akimotoite-pyroxene glass assemblages plot on a fractionation line in FeO-MgO diagram, with the host-rock pyroxene at the middle between the compositions of FeO-depleted akimotoite and the FeO-enriched pyroxene glass. These observations are different from previous reports of almost identical compositions of akimotoite, bridgmanite (Mg,Fe)SiO3-perovskite, or pyroxene glass to the host rock pyroxene (Chen et al. 2004; Ferroir et al. 2008; Ohtani et al. 2004; Tomioka and Fujino 1997), which is consistent with solid-state transformation from pyroxene to akimotoite and preexisting bridgmanite that could be vitrified. The observed fractionation trend and the granular shapes of akimotoite suggest crystallization from liquid produced by shock melting of the host-rock pyroxene, and the pyroxene glass matrix was probably quenched from the residual melt. However, this interpretation is inconsistent with the static experiments that expect crystallization of majorite (Mg,Fe)SiO3-garnet, instead of akimotoite, from pyroxene liquid (Sawamoto 1987). Our discovery raises the issue on formation mechanisms of the high-pressure polymorphs of pyroxene and places additional constraints on the post-shock high-pressure and high-temperature conditions of asteroids.
The Carlin-type gold deposit is best known in Nevada (USA) and SW China. In this paper, we report detailed field geology and mineral geochemical studies of gold-bearing pyrites from Lannigou ...Carlin-type Au deposit, SW China. Geological observations indicate that Lannigou Au deposit is a sediment-hosted gold deposit with quartz veins and controlled by steeply-dipping NW-trending F3, F6 fault and the intersection of F3 fault and NE-striking F2 fault, or secondary faults. As the main host mineral, arsenic pyrite is characterized by core-rim structure. And there is significant zonation in pyrite rim. EPMA data shows that core is characterized by low As, Au, Cu and higher Ni concentration. In contrast, rim has elevated concentration of As, Au and Cu. NanoSIMS mapping reveals the zonation of elements distribution including As, Au and Cu. According the textures and distributions of As and Au, we recognized three main stages of pyrites and late stage sulfides. Stage 1 pyrites were formed prior mineralization process. Stage 2, arsenic pyrites precipitated without Au. Stage 3, main Au precipitation taken place. Line scan of pyrite rims reveal that the peaks of As and Au were coupled with valley of δ34S in stage 3a and the correlations between As and Au are different in stage 3a and 3b. These observations indicate that Au precipitation mainly caused by fluid mixing. S isotope analyzed by NanoSIMS reveals a mixing trend between a magmatic-related fluid with δ34S value about 0‰ and a basin fluid with δ34S value about 18‰.
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•The distribution of ore-related elements and δ34S across individual pyrite crystals, from representative Carlin-type gold deposit in SW China, are determined by NanoSIMS.•The complex Au-As relationships revealed by NanoSIMS indicate multiple mechanisms of Au precipitation during mineralization.•The significant variation of δ34S value across individual pyrite grains reveal a mixing process of hydrothermal ore fluids. One of the origin could be trace element enriched fluid with mantle-like δ34S and another is a crustal fluid with elevated δ34S.
Sulfur isotope signatures of Au-bearing pyrite from Lannigou Au deposit, a typical Carlin-type Au deposit in SW China, provide valuable information about the origin of the ore-forming minerals. Analysis by NanoSIMS was used to determine S isotope compositions of Au-bearing pyrite and to map the grain-scale distributions of Au, Cu, As and S in pyrite from the deposit. Based on different textural pattern of pyrites revealed by back-scattered electron (BSE) images, they are divided into three types: Py-1 diagenetic pyrite without core-rim structure, Py-2 pyrite with an Au-free core and a rhythmically-zoned Au-bearing rim, Py-3 Au-bearing pyrite with rhythmic zoning across the entire grain. The element distributions and S isotope compositions of four paragenetic stages are recognized on the basis of textural observation. Py-1 grains and the Au-free homogeneous cores of zoned crystals were formed in Stage 1 while the Au-bearing rims of the zoned crystals with rhythmic zonation of As and Cu, and to a lesser degree Au, were formed in two superimposed stages: stage 2 formed the inner zone that is enriched in As alone; and stage 3 formed the outer zone that is enriched in both Au and As. Other sulfides such as realgar, cinnabar and stibnite are formed in the last stage. The relationship between Au and As distributions in pyrite rim is complicated, changing from coupled to decoupled at the nanoscale. Such complexity is interpreted to reflect fluctuation of fluid composition and temperature with time, which in turn affect the modes of occurrence of As and Au. It is inferred that As mainly occurs in the crystal lattice replacing S whereas Au is mainly present as nanoparticles that were trapped in pyrite during crystal growth. The Au-bearing rims of the zoned pyrite crystals are characterized by highly variable δ34S values from 1.1 to 18.1‰, which exceed the values of the Triassic calcareous host rocks (10–14‰). In contrast, the δ34S values of the Au-free cores of zoned pyrite crystals vary over a narrower interval and are mainly between 6 and 12‰, close to the values of pyrite crystals in the sedimentary country rocks. Our new analyses also reveals that the δ34S values of the Au-bearing fluids generally increase during the formation of the deposit. The observed S isotope variations are consistent with mixing between a magmatic-related fluid with mantle-like δ34S value (∼0‰) and a sedimentary or deep basin brine fluid with elevated δ34S value (>18‰), with an increasing contribution from the latter with time. The notably varied values of δ34S and the disseminations of Au and other trace elements such as As and Cu in pyrite crystals indicate that the process responsible for Au precipitation in this deposit occurred in an open hydrothermal system.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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