Planetary surface ages are extremely important to geologic evolution studies. For extraterrestrial bodies, the crater size-frequency distribution dating method, including a crater production function ...and a chronology function, was established based on the radiometric ages of Apollo and Luna samples from the Moon. Recently, the radiometric age of a sample from Chang'e-5 mission added a data point where there was previously a gap in sample ages, and an updated lunar chronology function was proposed. This research aims to recalculate the Martian surface dating model from the newly updated lunar chronology function. The calculation takes account of the differences in impact rates, impact velocities, surface gravities, the threshold diameters of craters' transition from the strength to gravity regime and from simple to complex crater structures on the Moon and Mars. We use the Neukum production function, although other production functions could also be implemented with our method. A series of Martian isochrons is derived, and an approximated analytical form production function is provided for convenient applications in future studies. The Martian chronology function is finally obtained through fitting crater frequencies larger than 1.0 km in diameter with the corresponding ages of the isochrons. The resultant Martian PF and CF in this research are largely comparable with previous results. Based on the refined lunar chronology function, our model will enhance the reliability of the estimating Martian surface ages and we suggest it be used in future studies.
•Martian isochrons are derived from lunar chronology function newly updated with Chang'E-5 sample data.•Difference from previous Martian chronology function is comparable to that for lunar chronology functions.•Martian isochrons are heavily influenced by the cratering ratio between the Moon and Mars.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The lunar Mg-suite magmatic rocks are commonly thought to represent mafic intrusions into the anorthositic flotation crust of the lunar magma ocean (LMO). Their geochronology is, therefore, important ...for constraining evolution models of the LMO. Petrogenetic models of the Mg-suite hold that their parent magmas were derived from primary LMO sources (Mg-cumulates, An-rich plagioclase, and melts enriched in KREEP—potassium, rare earth elements, and phosphorus). Previous radiogenic isotopic age interpretations of Mg-suite and putatively older, related ferroan anorthosites (FANs) overlap over a 200-million-year interval. The Apollo 78238 norite is an exemplary Mg-suite rock, with a relict coarse igneous texture modified by shock metamorphism. In-situ secondary ion mass spectrometry U-Pb analyses of zircon and baddeleyite in 78238 yield discordant arrays, attributed to recent impact metamorphism, with upper intercepts that constrain its crystallization age. The four oldest baddeleyite analyses give a weighted mean 207Pb/206Pb age of 4332 ± 18 Ma (2σ, MSWD = 0.06, P = 0.98), which is interpreted as the crystallization age of the norite. The overlap of the baddeleyite age with previously reported Sm-Nd and Pb-Pb mineral isochron ages for 78238 (Edmunson et al., 2009) supports a moderately fast cooling of the norite. Moreover, it is distinguishably younger than the most precisely dated sample of FAN (Apollo 60025), measured at 4360 ± 3 Ma by Sm-Nd and Pb-Pb mineral isochrons (Borg et al., 2011). Together with the baddeleyite 207Pb/206Pb age of Apollo Mg-suite troctolite 76535 at 4328 ± 8 Ma (White et al., 2020), the chronological record of the 78238 norite indicates a significant Mg-suite magmatic event at 4.33 Ga and a lower age limit on LMO differentiation.
•First SIMS U-Pb dating for Apollo norite 78238 is performed by 5 μm primary beam.•A baddeleyite grain in 78238 has a 207Pb/206Pb crystallization age of 4332 ± 18 Ma.•The 207Pb/206Pb age of 78238 is resolvably younger than the age of ferroan anorthosite 60025.•The 207Pb/206Pb age supports a pulse of the Mg-suite magmatism at ∼4330 Ma.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Although pure metallic iron (i.e. that with an Fe content of greater than 99%) commonly occurs in achondrites, and within the returned soil from asteroids or the Lunar surface, it is rarely found in ...ordinary chondrites meteorites. Abundant nanophase iron particles (np-Fe0) were identified in pyroxene glass, within the shock melt vein of Grove Mountains (GRV) 022115, which is an ordinary (L6) chondrite, with a shock stage determined as S5. The association of np-Fe0, highly defective high pressure clinoenstatite (HP-CEn), silica glass, as well as vesicles, embedded in a pyroxene glass selvage within the shock melt vein in this meteorite suggests that these phases formed as the result of decomposition of the host pyroxene grain, a process induced by the shock event that affected GRV 022115. The reaction to account for this mineral breakdown can be written as: FeSiO3 → Fe + SiO2 + 1/2O2 ↑ (MgSiO3 remain in the HP-CEn). The pressure and temperature condition attending this reaction are estimated at 20–23 GPa and over 1800 °C, as indicated by the surrounded high-pressure mineral assemblage: ringwoodite, majorite, and magnesiowüstite. This study provides evidence to the formation of np-Fe0 derived from pyroxene, and HP-CEn quenched metastably in such shocked vein could preserve the metastable phase transitions history record.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
China's first Mars mission Tianwen-1 successfully touched down the surface of the southern Utopia Planitia on 15th May 2021. In this study we investigate the geological characteristics of the target ...landing site (Site 1) and a backup landing site (Site 2) on Utopia Planitia for Tianwen-1 Mission. Site 1 is located in a topographic low and generally flat area to the southern Utopia basin, while Site 2 is located in the Utopia-Elysium transition zone. Several geological features indicative of the presence of a large reservoir of volatiles are identified and mapped in detail for both landing sites, including pitted cones, giant polygons, rampart and pancake craters. The volcanism-related morphologies, e.g., lava flows, lahars, and dikes, are also mapped for Site 2. The compositional analysis reveals little exposures of hydrous materials due to dust cover and/or lacking of data coverage over the regions. Crater counting analysis showed that the Site 1 has an absolute model age of ~3.68 Ga and ~3.45 Ga when including and excluding ghost craters, respectively. The absolute model age of Site 2 is ~3.34 Ga. Finally, the evolutionary history of the Utopia Planitia is discussed, and the related scientific hypotheses to be tested for the in situ exploration are suggested. Our study provides a framework for the Tianwen-1 in situ exploration, which will impose important constraints on the nature and evolution history of the northern lowlands.
•The detailed geological survey of the landing site of China's first Mars mission Tianwen-1 is conducted.•Various landforms within the landing site have been mapped and interpreted as the morphological indicators of water/ice.•The evolutionary history of the Utopia Planitia is discussed and the related scientific hypotheses to be tested are outlined.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Zircons and apatites in clasts and matrix from the Martian breccia NWA 7034 are well documented, timing ancient geologic events on Mars. Furthermore, in this study, zircon trace elemental content, ...apatite volatile content, and apatite volatile isotopic compositions measured in situ could constrain the evolution of those geologic events. The U‐Pb dates of zircons in basalt, basaltic andesite, trachyandesite igneous clasts, and the matrix are similar (4.4 Ga) suggesting intense volcanism on ancient Mars. However, two metamict zircon grains found in the matrix have an upper intercept date of ~4465 Ma in crystalline, whereas amorphous areas have a lower intercept date of 1634 ± 93 Ma. The younger date is consistent with the date of apatites (1530 ± 65 Ma), suggesting a metamorphic event that completely reset the U‐Pb system in both the amorphous areas of zircon and all apatites. δD values in all apatites negatively correlate with water content in a two‐endmember mixing trend. The D (δD up to 2459‰) and 37Cl heavy core (3.8‰) of a large apatite grain suggest a D‐, 37Cl‐rich fluid during the metamorphic event ~1.6 Ga ago, consistent with the trace elements Y, Hf and Ti and P in zircons. The fluid was also therefore P‐rich. The D‐, 37Cl‐poor H2O‐rich rim (<313‰) suggests the degassing of water from the Martian Cl‐poor interior at a later time. This D‐, 37Cl‐poor Martian mantle reservoir could have derived from volcanic intrusions postdating the younger metamorphic event recorded in NWA 7034.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
•The space weathering features of Apollo-15 lunar soil pyroxene and the adhered submicron-sized fragments were studied with FIB-TEM.•The npSiOx particles, as the by-product of space weathering, were ...observed for the first time in the Mg–Fe silicate fragment.•The coexisting npSiOx and npFe were probably formed directly in micrometeorite shock-induced melt, instead of in a solar-wind generated vapor deposit or irradiated rim.
Space weathering is an important process on the Moon and other airless celestial bodies. The most common space weathering effects are amorphization of the top surface of soil grains and formation of nanophase iron particles (npFe) within the partially amorphous rims. Hence, space weathering significantly affects optical properties of the surface of the Moon and other airless celestial bodies. Transmission electron microscope (TEM) analysis of Apollo 15 soil grains displays npFe (≤5 nm in size) embedded in the space-weathered rim (∼60 nm in thickness) of a pyroxene grain, consistent with previous studies. In contrast, submicron-sized fragments that adhere to the pyroxene grain show distinct space weathering features. Silicon oxide nanoparticles (npSiOx) were observed with npFe in a submicron-sized Mg–Fe silicate fragment. This is the first discovery of npSiOx as a product of space weathering. The npSiOx and the coexisting npFe are ∼10–25 nm in size, significantly larger than the typical npFe in the space weathered rim of the pyroxene grain. The coexisting npSiOx and npFe were probably formed directly in micrometeorite shock-induced melt, instead of in a solar-wind generated vapor deposit or irradiated rim. This new observation will shed light on space weathering processes on the Moon and airless celestial bodies.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The visible and near‐infrared imaging spectrometer on board the Yutu‐2 rover of Chang'E‐4 mission has conducted 2 sets of spectrophotometric measurements at two sites on its 10th lunar day. At each ...site, the reflectance spectra were measured on the same lunar regolith at different geometric configurations. The experiments reveal an increasing trend of the spectral reddening effect with the increasing phase angles, which may cause significant uncertainties on interpreting the maturity of the lunar regolith. Furthermore, the phase angles have significant effects on the 2‐μm band center and the 1‐μm band depth of the spectra, consequently on the estimation of mineral composition of the regolith. Finally, the derived average Hapke parameters using the in situ spectrophotometric measurements provide important ground‐truth for remote sensing observations.
Plain Language Summary
Olivine, pyroxenes and plagioclase, the major constituent minerals of the surface of the Moon, have diagnostic absorption features in their visible and near‐infrared reflectance spectra. These features, including the wavelength position of the absorption band center and the depth of the absorption band, can be used to identify the mineralogy of the observed surface. The slope of the reflectance spectral curve is another feature that can be used to describe the degree of how the surface materials interact with space environment. The Yutu‐2 rover on board the China's Chang'E‐4 mission has been equipped with a visible to near‐infrared spectrometer, to carry out in situ spectral measurements at varied illumination and azimuth angles. These measurements provided us an excellent chance to study the effects of measurement angles on these spectral features, which can help us better understand the mineralogical information of lunar surface.
Key Points
In situ spectrophotometric measurements by Chang'E‐4 Yutu‐2 rover show viewing geometry may affect band centers and depth of the spectra
Phase reddening coupled with space weathering effects on the spectra may cause significant uncertainties on interpreting the maturity of lunar regolith
The derived Hapke parameters from the in situ spectrophotometric measurements provide ground truth for both in situ and orbital observations
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Refractory calcium‐aluminum‐rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs) in chondritic meteorites are the earliest solids of our solar system, bearing the information of nebular ...condensation as well as accretion and asteroidal shock and metasomatism processes. While the compositions of refractory inclusions have been intensely studied for ~50 years, their physical properties such as shape and porosity are poorly constrained. Here, we present a microcomputed tomography (µCT) study on 16 refractory inclusions of condensate origin in five CV3 chondrites. We find that they are prolate or triaxial in shape with very rough morphologies. The CAIs have nodular textures and are thought to form by agglomerating individual nodules via collision‐induced bouncing and/or fragmentation, where the nodules were grown by gas–solid reactions during condensation. On the parent body, refractory inclusions from the CVR meteorite Leoville experienced intense shocks that led to the flattening of their shapes and lowering of their porosities. High‐temperature metasomatism in CVOxA meteorites and low‐temperature metasomatism in CVOxB meteorites do not seem to have large effects on the porosities of their refractory inclusions, which have similar ranges and pore‐size distributions. Instead, we infer that their pores are mostly inherited from the gas–solid condensation and subsequent agglomeration processes. The porosities of CAIs are higher than those of AOAs, which is mainly due to the high‐temperature sintering process of AOAs.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The petrologic and oxygen isotopic characteristics of calcium‐aluminum‐rich inclusions (CAIs) in CO chondrites were further constrained by studying CAIs from six primitive CO3.0‐3.1 chondrites, ...including two Antarctic meteorites (DOM 08006 and MIL 090010), three hot desert meteorites (NWA 10493, NWA 10498, and NWA 7892), and the Colony meteorite. The CAIs can be divided into hibonite‐bearing inclusions (spinel‐hibonite spherules, monomineralic grains, hibonite‐pyroxene microspherules, and irregular/nodular objects), grossite‐bearing inclusions (monomineralic grains, grossite‐melilite microspherules, and irregular/nodular objects), melilite‐rich inclusions (fluffy Type A, compact type A, monomineralic grains, and igneous fragments), spinel‐pyroxene inclusions (fluffy objects resembling fine‐grained spinel‐rich inclusions in CV chondrites and nodular/banded objects resembling those in CM chondrites), and pyroxene‐anorthite inclusions. They are typically small (98.4 ± 54.4 µm, 1SD) and comprise 1.54 ± 0.43 (1SD) area% of the host chondrites. Melilite in the hot desert and Colony meteorites was extensively replaced by a hydrated Ca‐Al‐silicate during terrestrial weathering and converted melilite‐rich inclusions into spinel‐pyroxene inclusions. The CAI populations of the weathered COs are very similar to those in CM chondrites, suggesting that complete replacement of melilite by terrestrial weathering, and possibly parent body aqueous alteration, would make the CO CAIs CM‐like, supporting the hypothesis that CO and CM chondrites derive from similar nebular materials. Within the CO3.0‐3.1 chondrites, asteroidal alteration significantly resets oxygen isotopic compositions of CAIs in CO3.1 chondrites (∆17O: −25 to −2‰) but left those in CO3.0‐3.05 chondrites mostly unchanged (∆17O: −25 to −20‰), further supporting the model whereby thermal metamorphism became evident in CO chondrites of petrologic type ≥3.1. The resistance of CAI minerals to oxygen isotope exchange during thermal metamorphism follows in the order: melilite + grossite < hibonite + anorthite < spinel + diopside + forsterite. Meanwhile, terrestrial weathering destroys melilite without changing the chemical and isotopic compositions of melilite and other CAI minerals.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Mineral olivine and Mg-rich spinel observed in Das crater were previously attributed to the excavation from the lunar lower crust or even mantle. To test this hypothesis, we developed a ...three-dimensional hydrocode SALEc to simulate the formation of such an elliptical crater. The hydrocode SALEc was examined and verified by comparing its results with experimental data and another code iSALE-2D. Based on the comparison between our SALEc's numerical results and observations, we found that Das crater can be formed by an impact with the projectile of 6.0 km in diameter, impact velocity of 10 km/s, and impact angle of 70° relative to the vertical. In the impact, the excavation depth of Das crater is ∼3.0 km, much less than the lunar crust thickness, hence the mineral olivine and Mg-rich spinel observed in this crater is unlikely originated from lunar lower crust or mantle. Numerical simulation results also show that some projectile materials can survive in this impact and are distributed in the downrange crater floor. Given the abundant olivine in many asteroids, we propose that olivine observed in Das crater is most probably originated from projectile remnants instead of excavation from the depth.
•We developed a three-dimensional hydrocode to simulate the formation of lunar craters.•Lunar Das crater was impacted by a 6.0 km-diameter projectile at an angle of 70° relative to the vertical.•The maximum excavation depth was estimated ∼3.0 km and olivine in Das crater is probably from projectile remnant.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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