North Ray Research Articles

Chemical release risk assessment in earthquake: Natech event scenario

IntroductionIn recent decades, an increase in natural disasters has led to the Natech events occurrence, which are technological accidents triggered by natural hazards. This study aims to assess the risk of chemical release of the H2S toxic gas following an earthquake from the refinery. MethodThe Natech risk assessment was carried out in potential earthquake risk scenarios via a semi-quantitative method using Rapid-N software. The reference scenario was obtained using the Australian SMUG Model, which has presented precise prioritization. FindingsThe Natech risk assessment has shown 40 possible earthquake risk scenarios from 5 enclosing Faults in Tehran (North Tehran, Mosha, North Ray, South Ray, and Kahrizak) with an extension of more than 15 km. The earthquake moment magnitudes of 7.5, 7.1, 6.5, and 5.9 were obtained on the Richter scale and at two Focal depths of 5 and 10 km. The South-Ray Fault (HSR-1) was selected as the reference scenario with a moment magnitude of 7.5 on the Richter scale at a Focal depth of 5 km and a distance of 5.5 km from the earthquake epicenter. The highest probability of Natech risk has shown the release of H2S toxic gas in an area with a radius of 6.59 km from the studied vessel in atmospheric stability conditions. ConclusionLegislation in line with risk reduction, planning for the transfer of potentially dangerous industries to outside urban areas, monitoring land use laws, and promoting coordination between the government, industries, and people in the management of risks caused by industries containing hazardous substances and processes, assessing the risk of Natech events and their consequences, strengthening risk communication and the installation of early warning systems, and public education to adopt personal and socially safe behaviors when facing natural disasters are recommended.

Slopes of Lunar Crater Size‐Frequency Distributions at Copernican‐Aged Craters

AbstractCraters on the lunar surface can provide valuable information about the timing and sequence of surface‐forming processes on the Moon. A commonly used method for age determination is the analysis of the crater size‐frequency distribution (CSFD) to which a production function (PF) is fitted that represents the size‐frequency distribution of the impactors. However, the commonly used PF of Neukum (1983) is valid for crater diameters between 10 m and 300 km. Neukum et al. (2001, https://doi.org/10.1007/978-94-017-1035-0_3) revised the PF for crater diameters of 100 m–200 km. However, it is suggested to also be valid for the diameter range of 10 m–300 km as well. To assess whether we can extend a PF to craters ≤10 m in diameter, we investigated the slopes of the CSFDs of small craters formed on ejecta of young Copernican‐aged craters Giordano Bruno, Moore F, North Ray, and South Ray. A PF for smaller diameters would allow dating of young geological units, which are typically small, and would reduce the statistical error in age determinations, since smaller craters are more abundant. However, small craters are strongly influenced by geological factors, such as target properties, crater degradation, and secondary craters. For craters between 10 and 20 m we obtain a steeper CSFD slope than Neukum's proposed −3 slope (cumulative), whereas for craters ≤10 m the slope is about −3. We conclude that the PF of Neukum (1983) provides a reasonable CSFD slope for smaller craters, although it was not developed for this crater diameter range.

Noble gas exposure ages of samples from Cone and North Ray craters: Implications for the recent lunar cratering chronology

AbstractCosmic ray exposure (CRE) ages of rocks that were ejected by the impacts that created Cone and North Ray craters provide two crucial calibration points at <100 Ma for the lunar cratering chronology function, which relates the crater density of geological units on the Moon to their absolute age. To reassess the formation ages of these two craters, we determine here the accumulated abundances of “cosmogenic” noble gas nuclides (3Hecosm, 21Necosm, 38Arcosm), as well as the corresponding CRE ages, in six Apollo 14 rocks (i.e., one breccia and five basalts) and two Apollo 16 anorthosites that were collected near the rims of Cone and North Ray craters, respectively. Although noble gas concentrations allow CRE ages to be derived, the calculated 21Ne and 38Ar exposure ages of a given sample cover a significant range of values because published empirical or theoretical production rates of cosmogenic nuclides are highly variable. Nonetheless, it is evident that mare basalts 14053 and 14072 as well as breccia 14068, which were collected near the rim of Cone crater, were exposed at the lunar surface more recently than the three KREEP basalts (14073, 14077, 14078) collected farther away. The 38Ar exposure ages of anorthosites 67075 and 67955 from North Ray crater slightly exceed those of samples 14053, 14068, and 14072. These results confirm that Cone crater is younger than North Ray crater. However, the formation ages of Cone and North Ray craters have larger uncertainties than previously acknowledged. This implies that the uncertainties of noble gas exposure ages should be taken into account when remotely dating young surfaces on the Moon and on other planetary bodies in the solar system.

Boulder Distributions Around Young, Small Lunar Impact Craters and Implications for Regolith Production Rates and Landing Site Safety

AbstractWe use Lunar Reconnaissance Orbiter Camera Narrow Angle Camera images to characterize boulder populations around six small (<1 km), young (<200 Ma) impact craters near spacecraft landing sites. The Narrow Angle Camera boulder counts are used to analyze how boulder distributions vary around craters of different sizes and ages. These comparisons inform how various properties affect the distance to which boulders are ejected and the size and density of boulders produced by an impact event. The counts show that boulder population densities decrease with crater age, with few boulders remaining at craters older than a few hundred million years, consistent with results of other studies of boulder degradation rates on the Moon. Variations in boulder distributions around younger craters may provide information regarding impact conditions; South Ray crater has a larger population of small boulders than the larger North Ray crater, which could be explained by variations in impact velocity. Large craters generally excavate more boulders than smaller craters, and the size of the largest boulder ejected is related to crater size by a power‐law function. Larger boulders occur closer to the crater rim (within 2–4 crater radii), whereas smaller boulders occur at all distances. The density of boulders is greater near the crater rim and decreases with increasing radial distance; this data can aid in establishing safe landing zones for future missions. Analyzing boulder distributions across craters of varying ages allows us to test models of boulder breakdown rates, with implications for understanding the Moon's regolith production rate.

Origin of lunar fragmental matrix breccias—Highly siderophile element constraints

AbstractEjecta at North Ray crater (Apollo 16) sampled a unique section of the lunar highlands not accessible at most other landing sites and provide important constraints on the composition of late accreted materials. New data on multiple aliquots of four fragmental matrix breccias and a fragment‐laden melt breccia from this site display a variety of highly siderophile element patterns which may represent the signatures of volatile element‐depleted carbonaceous chondrite‐like material, primitive achondrite, differentiated metal, and an impactor component that cannot be related to known meteoritic material. The latter component is prevalent in these rocks besides characterized by depletions in Re and Os compared to Ir, Ru and Pt, chondritic Re/Os, and a gradual depletion of Pd and Au. The observed characteristics are more consistent with fractionations by nebular processes, like incomplete condensation or evaporation, than with lunar crustal processes, like partial melting or volatilization. The impactor signature preserved in these breccias may stem from primitive meteorites with a refractory element composition moderately different from known chondrites. The presence of distinct impactor components within the North Ray crater breccias together with observed correlations of characteristic element ratios (e.g., Re/Os, Ru/Pt, Pd/Ir) in different impact lithologies of four Apollo landing sites constrains physical mixing processes ranging from the scale of gram‐sized samples to the area covered by the Apollo missions.

Correlations between ejecta boulder spatial density of small lunar craters and the crater age

This work explores the quantitative correlation between the ejecta boulder number density and crater age for seven craters from ∼200 m to 1 km in diameter. Using the selected set of LRO NAC images with resolution ∼0.5 m/pixel we mapped and counted the ejected boulders larger than 3 m across inside the one-crater-radius-wide concentric annulus (or its part) from crater rim, for craters South Ray, Unnamed A, Unnamed B, Cone, North Ray, Unnamed D and Camelot. This study partly repeats the work of Basilevsky et al. (2013, 2015b) on the study of spatial density of boulders of small lunar craters of known formation age, but based on the larger counting areas, thus the larger numbers of ejecta boulders were counted. The results from our study are certainly statistically more reliable.This study does not only confirm the results of Basilevsky et al. (2013, 2015b) that spatial densities of boulders generally decrease with crater age, but also find the mare craters are generally more rockiness than highland craters if given similar formation ages, which is interpreted as the effect of the higher mechanical strength of mare rocks (basalts) comparing to that of highland rocks (fragmental breccias).We also found the quantitative relations between boulder spatial density (>3 m) and the age of mare craters and highland craters, respectively. The applicability tests show that these relations are only suitable for craters smaller than 1 km in size. This is interpreted as the excavation of less fragmented bedrocks due to deeper excavation depth for large size craters (>1 km), resulting in a different boulder size distribution in comparison to that for craters < 1 km.This study improves the understanding of the boulder size distribution for crater <1 km in size, and provides a new perspective on the crater age determination using boulder spatial density.

Multi-hazard failure probability analysis of gas pipelines for earthquake shaking, ground failure and fire following earthquake

This paper was aimed to provide a quantitative failure probability analysis for multiple hazards. To achieve this, the 1724-kPa (250 Psi) gas pipelines of one of the district neighborhoods of Tehran metropolitan are analyzed to establish the probability of damage against earthquake, fire and liquefaction as a multi-hazard case study. The pipeline is approximately 4 km long and is divided into 14 segments, each of which has 300 m length. We used probabilistic analysis to identify the sources of earthquakes in the area. We calculated the probability that an earthquake with a given maximum magnitude will occur, the probability of liquefaction, that of post-earthquake fires, and the probability of pipeline failure for each segment. In order to take into account uncertainty in the location of epicenters, different points on the North Ray fault were randomly selected as epicenters, and the analysis was carried out for each point. Finally, based on the proposed method, the upper bound of failure probability of the main pipeline resulting from multiple hazards was estimated to be 65.7 %. If ductile pipelines were installed, this amount could be reduced to 32.7 % which shows a reduction of 51.79 % of the upper bound of failure probability.

Crystal accumulation in a 4.2 Ga lunar impact melt

The ages of lunar impact basins and the role of fractional crystallization in producing compositional heterogeneity of lunar melt sheets are long-standing problems with significant implications for solar system dynamics and the petrologic evolution of the lunar crust. Here we document the formation of a basin-scale impact on the Moon at 4.20±0.07Ga based on the 147Sm–143Nd isochron age of a magnesian, noritic anorthosite melt rock from lunar breccia 67955. Major element compositions of plagioclase and mafic silicates in the melt rock imply a substantial component of primary Mg-suite cumulates or related lithologies in the pre-impact crustal stratigraphy. Trace element compositions of the plagioclase, including diagnostic ratios such as Sr/Ba, are also mostly similar to those in plagioclase from Mg-suite cumulates, with a small number of grains trending toward compositions observed in ferroan anorthosites. Mineral-melt distribution coefficients applied to trace element compositions of the 67955 plagioclase and pyroxene predict parental melt compositions that contrast strongly with the bulk rock. Compared to the whole rock, parental melts calculated from the plagioclase are enriched in REE (ΣREELa–Yb=131–885, average 619ppm vs. 39.8ppm) and they have more fractionated REE patterns (La/Ybn=1.2–9.8, average 4.9 vs. 1.5) with deep negative Eu anomalies (Eu/Eu∗=0.09–0.40 vs. 1.36). Trace element data for the pyroxenes also imply incompatible-element enriched parental melts. Subsolidus equilibration between the plagioclase and the pyroxene apparently rotated the REE patterns, but the conclusion that the parental melt was highly enriched in REE relative to the whole rock appears robust. Quantitative modeling shows that fractional crystallization of the 67955 whole rock composition cannot reproduce the range of Ba, Sr, Ti, and La concentrations measured in the 67955 plagioclase. Rather, the models require an initial melt composition that was strongly enriched in these elements, and they suggest that fractional crystallization became less efficient as crystallization proceeded. The contrast between the inferred parental melt composition and the bulk rock implies formation of the 67955 noritic anorthosite as a crystal cumulate, and that the cogenetic residual melt was strongly enriched in incompatible elements. If so, this would be the first documented example of fractional crystallization in a lunar impact melt sheet. The petrological and geochemical characteristics of the 67955 noritic anorthosite suggest that it formed by an impact in the Procellarum-KREEP Terrane, and was transported to the Apollo 16 site as Imbrium ejecta. Inheritance of ejecta related to this pre-Imbrium basin may contribute to the common occurrence of ∼4.2Ga 40Ar–39Ar plateau ages in breccia clasts and regolith fragments from the rim of North Ray crater. In that case, those data may provide no constraints on the age of the Nectaris basin, despite its proximity to the Apollo 16 site.

The production of small primary craters on Mars and the Moon

We model the primary crater production of small (D<100m) primary craters on Mars and the Moon using the observed annual flux of terrestrial fireballs. From the size–frequency distribution (SFD) of meteor diameters, with appropriate velocity distributions for Mars and the Moon, we are able to reproduce martian and lunar crater-count chronometry systems (isochrons) in both slope and magnitude. We include an atmospheric model for Mars that accounts for the deceleration, ablation, and fragmentation of meteors. We find that the details of the atmosphere or the fragmentation of the meteors do not strongly influence our results. The downturn in the crater SFD from atmospheric filtering is predicted to occur at D∼10–20cm, well below the downturn observed in the distribution of fresh craters detected by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) or the Mars Reconnaissance Orbiter (MRO) Context Camera (CTX). Crater counts are conducted on the ejecta blanket of Zunil crater and the interior of Pangboche crater on Mars and North Ray and Cone craters on the Moon. Our model isochrons produce a similar slope and age estimate for the formation of Zunil crater as the Hartmann production function (∼1Ma). We derive an age of 35.1Ma for Pangboche when accounting for the higher elevation (>20km higher than Zunil), a factor ∼2 younger than estimated using the Hartmann production function which assumes 6mbar surface pressure. We estimate ages of 52.3Ma and 23.9Ma for North Ray and Cone crater respectively, consistent with cosmic ray exposure ages from Apollo samples. Our results indicate that the average cratering rate has been constant on these bodies over these time periods. Since our Monte Carlo simulations demonstrate that the existing crater chronology systems can be applied to date young surfaces using small craters on the Moon and Mars, we conclude that the signal from secondary craters in the isochrons must be relatively small at these locations, as our Monte Carlo model only generates primary craters.

Real-Time Mapping of PGA Distribution in Tehran Using TRRNet and peeqMap

Tehran megacity, the political and economical capital of Iran with population of more than eight million residents, is situated in the seismically active zone of Alborz. The seismicity pattern of this zone shows occurrence of large earthquakes in long time periods (Masson et al. , 2005). Several large earthquakes such as the 855 A.D. M s 7.1, the 958 A.D. M s 7.7, and the 1117 A.D. M s 7.2 in the historical seismic catalog of Tehran and surrounding area proves that the city has a high level of seismic risk (Fig. 1). The last disastrous example among these earthquakes was in 1830, and the city is waiting for the next large earthquake (Ambraseys and Melville, 1982; Ashtari‐Jafari, 2010). Several active faults surround Tehran including North Tehran fault, Eyvanekey fault, North and South Ray faults (Fig. 1). Apart from existence of several active faults around the city, fast growth of population and urbanization in previous decades, and lack of strong regulations for urban development increased the vulnerability of Tehran to moderate to large earthquakes (Amini‐Hosseini et al. , 2009). Figure 1. Map showing major active faults (Hessami et al. , 2003), and seismicity around Tehran. Circles, epicenters of M s>6 earthquakes; numbers, the year of earthquake occurrence. The historical earthquakes are from Ambraseys and Melville (1982). Star, the epicenter of the 17 October 2009 ( M w 4.0). NRF and SRF in the dashed square area, closely surrounding the city, refer to South Ray fault and North Ray fault, respectively. Topographic contours at 200 m intervals of the boxed area are shown in Figure 3. Mindful of the seismic risk faced by the city, the Tehran Rapid Response Network (TRRNet) has been installed in the Tehran metropolitan area …

The bombardment history of the Moon as recorded by 40Ar‐39Ar chronology

AbstractNew petrography and 40Ar‐39Ar ages have been obtained for 1–3 mm sized rock fragments from Apollo 16 Station 13 soil 63503 (North Ray crater ejecta) and chips from three rocks collected by Apollo 16 and Apollo 17 missions. Selection of these samples was aimed at the old 40Ar‐39Ar ages to understand the early history of the lunar magnetic field and impact flux. Fifteen samples were studied including crustal material, polymict feldspathic fragmental breccias, and impact melts. The impact ages obtained range between approximately 3.3 and 4.3 billion years (Ga). Polymict fragmental breccia 63503,1 exhibits the lowest signs of recrystallization observed and a probable old relic age of 4.547 ± 0.027. The plateau age of 4.293 ± 0.044 Ga obtained for impact melt rock 63503,13 represents the oldest known age for such a lithology. Possibly, this age represents the minimum age for the South Pole‐Aitken (SPA) Basin. In agreement with literature data, these results show that impact ages &gt;3.9 Ga are found in lunar rocks, especially within soil 63503. Impact exhumation of deep‐seated warm crustal material onto the lunar surface is considered to explain the common 4.2 Ga ages obtained for weakly shocked samples from soil 63503 and Apollo 17. This would directly imply that one or more basin‐forming events occurred at that time. Some rock fragments showing none to limited petrologic features indicate thermal annealing. These rocks may have lost Ar while resident within the hot‐ejecta of a large basin. Concurrent with previous studies, these results lead us to advocate for a complex impact flux in the inner solar system during the initial approximately 1.3 Ga.

How old are young lunar craters?

The accurate definition of the lunar cratering chronology is important for deriving absolute model ages across the lunar surface and throughout the Solar System. Images from the Lunar Reconnaissance Orbiter Narrow Angle Cameras and Wide‐Angle Camera and the SELENE/Kaguya Terrain Camera provide new opportunities to investigate crater size‐frequency distributions (CSFDs) on individual geological units at lunar impact craters. We report new CSFD measurements for the Copernican‐aged craters North Ray, Tycho, and Copernicus, which are crucial anchor points for the lunar cratering chronology. We also discuss possible reasons for an age discrepancy observed between the impact melt and ejecta units. Our CSFDs for North Ray and Tycho crater ejecta deposits are consistent with earlier measurements. However, for Copernicus crater and one of its rays, we find significantly lower cumulative crater frequencies than previous studies. Our new results for Copernicus crater fit the existing lunar absolute chronologies significantly better than the previous counts. Our derived model ages of the ejecta blankets of North Ray, Tycho, and Copernicus agree well with radiometric and exposure ages of the Apollo 16, 17, and 12 landing sites, respectively, and are generally consistent with a constant impact rate over the last 3 Ga. However, small variations of the impact rate cannot be resolved in our data and require further investigations.

Imbrium provenance for the Apollo 16 Descartes terrain: Argon ages and geochemistry of lunar breccias 67016 and 67455

In order to improve our understanding of impact history and surface geology on the Moon, we obtained 40Ar– 39Ar incremental heating age data and major + trace element compositions of anorthositic and melt breccia clasts from Apollo 16 feldspathic fragmental breccias 67016 and 67455. These breccias represent the Descartes terrain, a regional unit often proposed to be ejecta from the nearby Nectaris basin. The goal of this work is to better constrain the emplacement age and provenance of the Descartes breccias. Four anorthositic clasts from 67016 yielded well-defined 40Ar– 39Ar plateau ages ranging from 3842 ± 19 to 3875 ± 20 Ma. Replicate analyses of these clasts all agree within measurement error, with only slight evidence for either inheritance or younger disturbance. In contrast, fragment-laden melt breccia clasts from 67016 yielded apparent plateau ages of 4.0–4.2 Ga with indications of even older material (to 4.5 Ga) in the high-T fractions. Argon release spectra of the 67455 clasts are more variable with evidence for reheating at 2.0-2.5 Ga. We obtained plateau ages of 3801 ± 29 to 4012 ± 21 Ma for three anorthositic clasts, and 3987 ± 21 Ma for one melt breccia clast. The anorthositic clasts from these breccias and fragments extracted from North Ray crater regolith ( Maurer et al., 1978) define a combined age of 3866 ± 9 Ma, which we interpret as the assembly age of the feldspathic fragmental breccia unit sampled at North Ray crater. Systematic variations in diagnostic trace element ratios (Sr/Ba, Ti/Sm, Sc/Sm) with incompatible element abundances show that ferroan anorthositic rocks and KREEP-bearing lithologies contributed to the clast population. The Descartes breccias likely were deposited as a coherent lithologic unit in a single event. Their regional distribution suggests emplacement as basin ejecta. An assembly age of 3866 ± 9 Ma would be identical with the accepted age of the Imbrium basin, and trace element compositions are consistent with a provenance in the Procellarum-KREEP Terrane. The combination of age and provenance constraints points toward deposition of the Descartes breccias as ejecta from the Imbrium basin rather than Nectaris. Diffusion modeling shows that the older apparent plateau ages of the melt brecia clasts plausibly result from incomplete degassing of ancient crust during emplacement of the Descartes breccias. Heating steps in the melt breccia clasts that approach the primary crystallization ages of lunar anorthosites show that earlier impact events did not completely outgas the upper crust.

Petrography and geochemistry of five new Apollo 16 mare basalts and evidence for post‐basin deposition of basaltic material at the site

Abstract— We present the petrography and geochemistry of five 2–4 mm basalt fragments from the Apollo 16 regolith. These fragments are 1) a high‐Ti vitrophyric basalt compositionally similar to Apollo 17 high‐Ti mare basalts, 2) a very high‐Ti vitrophyric basalt compositionally similar to Apollos 12 and 14 red‐black pyroclastic glass, 3) a coarsely crystalline high‐Al basalt compositionally similar to group 5 Apollo 14 high‐Al mare basalts, 4) a very low‐Ti (VLT) crystalline basalt compositionally similar to Luna 24 VLT basalts, and 5) a VLT basaltic glass fragment compositionally similar to Apollo 17 VLT basalts. High‐Ti basalt has been reported previously at the Apollo 16 site; the other basalt types have not been reported previously. As there are no known cryptomaria or pyroclastic deposits in the highlands near the Apollo 16 site (ruling out a local origin), and scant evidence for basaltic material in the Apollo 16 ancient regolith breccias or Apollo 16 soils collected near North Ray Crater (ruling out a basin ejecta origin), we infer that the basaltic material in the Apollo 16 regolith originated in maria near the Apollo 16 site and was transported laterally to the site by small‐ to medium‐sized post‐basin impacts. On the basis of TiO2 concentrations derived from the Clementine UVVIS data, Mare Tranquillitatis (˜300 km north) is the most likely source for the high‐Ti basaltic material at the Apollo 16 site (craters Ross, Arago, Dionysius, Maskelyne, Moltke, Sosigenes, Schmidt), Mare Nectaris/Sinus Asperitatis (˜220 km east) is the most likely source for the low‐Ti and VLT basaltic material (craters Theophilus, Madler, Torricelli), and a large regional pyroclastic deposit near Mare Vaporum (˜600 km northwest) is the most likely source region for pyroclastic material (although no source craters are apparent in the region).

Stratigraphy and Isotope Ages of Lunar Geologic Units: Chronological Standard for the Inner Solar System

The absolute ages of cratered surfaces in the inner solar system, including Mars, are derived by extrapolation from the impact flux curve for the Moon which has been calibrated on the basis of absolute ages of lunar samples. We reevaluate the lunar flux curve using isotope ages of lunar samples and the latest views on the lunar stratigraphy and the principles of relative and absolute age dating of geologic surface units of the Moon. The geological setting of the Apollo and Luna landing areas are described as far as they are relevant for this reevaluation. We derive the following best estimates for the ages of the multi-ring basins and their related ejecta blankets and present alternative ages for the basin events (in parentheses): 3.92 ± 0.03 Gyr (or 3.85 ± 0.05 Gyr) for Nectaris, 3.89 ± 0.02 Gyr (or 3.84 ± 0.04 Gyr) for Crisium, 3.89 ± 0.01 Gyr (or 3.87 ± 0.03 Gyr) for Serenitatis, and 3.85 ± 0.02 Gyr (or 3.77 ± 0.02 Gyr) for Imbrium. Our best estimates for the ages of the mare landing areas are: 3.80 ± 0.02 Gyr for Apollo 11 (old surface), 3.75 ± 0.01 Gyr for Apollo 17, 3.58 ± 0.01 Gyr for Apollo 11 (young surface), 3.41 ± 0.04 Gyr for Luna 16, 3.30 ± 0.02 Gyr for Apollo 15, 3.22 ± 0.02 Gyr for Luna 24, and 3.15 ± 0.04 Gyr for Apollo 12. The ages of Eratosthenian and Copernican craters remain: ~ 2.1 (?) Gyr (Autolycus), 800 ± 15 Myr (Copernicus), 109 ± 4 Myr (Tycho), 50.3 ± 0.8 (North Ray crater, Apollo 16), and 25.1 ± 1.2 (Cone crater, Apollo 14). When plotted against the crater densities of the relevant lunar surface units, these data result in a revised lunar impact flux curve which differs from the previously used flux curve in the following respects: (1) The ages of the stratigraphically most critical impact basins are notably younger, (2) the uncertainty of the calibration curve is decreased, especially in the age range from about 4.0 to 3.0 Gyr, (3) any curve for ages older than 3.95 Gyr (upper age limit of the Nectaris ejecta blanket) is abandoned because crater frequencies measured on such surface formations cannot be correlated with absolute ages obtained on lunar samples. Therefore, the impact flux curve for this pre-Nectarian time remains unknown. The new calibration curve for lunar crater retention ages less than about 3.9 Gyr provides an updated standard reference for the inner solar system bodies including Mars.

Lunar nitrogen: indigenous signature and cosmic-ray production rate

Abstract Indigenous lunar nitrogen composition and abundances have been determined in old ferroan anorthosite 60025 and in anorthositic breccia 67915 from North Ray Crater, as well as in 55 cm deep volcanic glasses of 74001 double-drive core from Shorty Crater. Also included in the set is the well-documented lunar basalt 75075, collected near the Camelot Crater. Indigenous lunar N abundances are low (at ppm level), but there is some variation between glass-rich cores, mare basalts and anorthosites. The uniform indigenous N isotopic signature of δ 15 N=+13.0±1.2‰, is consistent with data reported previously for Shorty Crater samples. The indigenous δ 15 N cannot account for the light nitrogen component, observed in the lunar regolith samples. We have determined cosmic-ray production rates P ( 15 N) for the above rocks and the drill core samples. The average production rate estimate (for low shielding) of P ( 15 N)=5.8±0.6 pg 15 N/g/Ma is ∼60% higher than published lunar 15 N production rates, but consistent with the meteoritic production rate derived from silicates in the Enon meteorite, when normalized to 2π-irradiation geometry. From the observed cosmogenic 15 N excesses and the reported cosmogenic 21 Ne abundances in core 74001 we derive a ( 15 N C / 21 Ne C ) production rate ratio of 4.0±0.3 for silicates.

On the relationship between the Apollo 16 ancient regolith breccias and feldspathic fragmental breccias, and the composition of the prebasin crust in the Central Highlands of the Moon

Abstract Two types of texturally and compositionally similar breccias that consist largely of fragmental debris from meteorite impacts occur at the Apollo 16 lunar site: Feldspathic fragmental breccias (FFBs) and ancient regolith breccias (ARBs). Both types of breccia are composed of a suite of mostly feldspathic components derived from the early crust of the Moon and mafic impact‐melt breccias produced during the time of basin formation. The ARBs also contain components, such as agglutinates and glass spherules, indicating that the material of which they are composed occurred at the surface of the Moon as fine‐grained regolith prior to lithification of the breccias. These components are absent from the FFBs, suggesting that the FFBs might be the protolith of the ARBs. However, several compositional differences exist between the two types of breccia, making any simple genetic relationship implausible. First, clasts of mafic impact‐melt breccia occurring in the FFBs are of a different composition than those in the ARBs. Also the feldspathic “prebasin” components of the FFBs have a lower average Mg/Fe ratio than the corresponding components of the ARBs; the average composition of the plagioclase in the FFBs is more sodic than that of the ARBs; and there are differences in relative abundances of rare earth elements. The two breccia types also have different provenances: the FFBs occur primarily in ejecta from North Ray crater and presumably derive from the Descartes Formation, while the ARBs are restricted to the Cayley plains. Together these observations suggest that although some type of fragmental breccia may have been a precursor to the ARBs, the FFBs of North Ray crater are not a significant component of the ARBs and, by inference, the Cayley plains. The average compositions of the prebasin components of the two types of fragmental breccia are generally similar to the composition of the feldspathic lunar meteorites. With 30–31% Al2O3, however, they are slightly richer in plagioclase than the most feldspathic lunar meteorites (∼29% Al2O3), implying that the crust of the early central nearside of the Moon contained a higher abundance of highly feldspathic anorthosite than typical lunar highlands, as inferred from the lunar meteorites. The ancient regolith breccias, as well as the current surface regolith of the Cayley plains, are more mafic than (1) prebasin regoliths in the Central Highlands and (2) regions of highlands presently distant from nearside basins because they contain a high abundance (∼30%) of mafic impact‐melt breccias produced during the time of basin formation that is absent from other regoliths.

Cogenetic rock fragments from a lunar soil: Evidence of a ferroan noritic-anorthosite pluton on the Moon

The impact that produced North Ray Crater, Apollo 16 landing site, exhumed rocks that include relatively mafic members of the lunar ferroan anorthositic suite. Bulk and mineral compositions indicate that a majority of 2–4 mm lithic fragments from sample 67513, including impact breccias and monomict igneous rocks, are related to a common noritic-anorthosite precursor. Compositions and geochemical trends of these lithic fragments and of related samples collected along the rim of North Ray Crater suggest that these rocks derived from a single igneous body. This body developed as an orthocumulate from a mixture of cumulus plagioclase and mafic intercumulus melt, after the plagioclase had separated from any cogenetic mafic minerals and had become concentrated into a crystal mush (∼70 wt% plagioclase, 30 wt% intercumulus melt). We present a model for the crystallization of the igneous system wherein “system” is defined as cumulus plagioclase and intercumulus melt. The initial accumulation of plagioclase is analogous to the formation of thick anorthosites of the terrestrial Stillwater Complex; however, a second stage of formation is indicated, involving migration of the cumulus-plagioclase—intercumulus-melt system to a higher crustal level, analogous to the emplacement of terrestrial massif anorthosites. Compositional variations of the lithic fragments from sample 67513 are consistent with dominantly equilibrium crystallization of intercumulus melt. The highly calcic nature of orthocumulus pyroxene and plagioclase suggests some reaction between the intercumulus melt and cumulus plagioclase, perhaps facilitated by some recrystallization of cumulus plagioclase. Bulk compositions and mineral assemblages of individual rock fragments also require that most of the mafic minerals formed in close contact with cumulus plagioclase, not as separate layers. The distribution of compositions (and by inference, modes) has a narrow peak at anorthosite and a broader, larger peak at noritic anorthosite.Characteristics of the samples and their geochemical trends imply an origin in a system that was large relative to the (unknown) size of the impact that produced the brecccas of ferroan noritic-anorthosite composition that were excavated later by the formation of North Ray Crater, and they appear to be consistent with an origin of the suite within a perched plagioclase cumulate. If the Moon's crust formed by accumulation of plagioclase in a magma ocean, ferroan noritic anorthosite, formed as an orthocumulate, is an alternative to extensive adcumulus formation of ferroan anorthosite (>90 vol% plagioclase). This provides a relatively mafic ferroan anorthositic component (∼15 vol% mafics), which is required by mass-balance models of compositions of polymict lunar-crustal materials. The inferred bulk composition of the system of cumulus plagioclase and intercumulus melt is similar to that of ferroan regolith breccia MacAlpine Hills 88104/5, a lunar-highland meteorite, and may represent a common and widespread component of the Moon's early highland crust.

Fragments of ancient lunar crust: Petrology and geochemistry of ferroan noritic anorthosites from the Descartes region of the Moon

Clasts of ferroan noritic anorthosite from Apollo 16 breccia 67016 have mineralogical and geochemical affinities with pristine ferroan anorthosites and therefore may represent primary igneous rocks from the lunar crust. The textures of these clasts document a complex history involving magmatic crystallization, brecciation, subsolidus recrystallization, and sulfide metasomatism. Nonetheless, the major, minor, and trace element compositions of their minerals, as determined by electron and proton microprobe, show that the clasts are essentially monomict and belong to the ferroan anorthositic suite of lunar highlands rocks. The low bulk Ni contents, low Ni Co ratios, and ancient SmNd isotopic age (≥4.5 Ga; Alibert et al., 1994) of the clasts are consistent with this interpretation. Strontium and gallium contents of plagioclase in the clasts show that their parental magma was depleted in Ga relative to Sr by a factor of about 30 relative to carbonaceous chondrites. This depletion of Ga, which is both moderately volatile and moderately siderophile, probably reflects volatile loss from the Moon rather than extraction of metal. The parental magma from which these clasts originally crystallized was enriched in Sr by about 4–6X relative to proposed bulk Moon compositions, which implies either that ferroan anorthosites crystallized late in the evolution of a lunar magma ocean, or that their parental magma was a basaltic partial melt. Bulk major and trace element compositions of these clasts are remarkably similar to that of the average upper crust of the Moon, which suggests that igneous ferroan noritic anorthosite such as that found in the North Ray Crater breccias and soils may be a significant primary component of the lunar crust. The ferroan noritic anorthosite clasts in 67016 are unusual among lunar samples for their abundance of troilite, and for the evidence of metasomatic introduction of volatile chalcophile elements such as Cu, Zn, Ni, Sb, and Se. Anhydrous COSCl vapors are the most likely transport agent for these metals, which would be more consistent with an indigenous lunar origin for the volatiles rather than a cometary or meteoritic source.

Compositional variation in Apollo 16 impact-melt breccias and inferences for the geology and bombardment history of the Central Highlands of the Moon

High-precision data for the concentrations of a number of lithophile and siderophile elements were obtained on multiple subsamples from 109 impact-melt rocks and breccias (mostly crystalline) from the Apollo 16 site. Compositions of nearly all Apollo 16 melt rocks fall on one of two trends of increasing Sm concentration with increasing Sc concentration. The Eastern trend (lower Sm Sc , Mg Fe , and Sm Yb ratios) consists of compositional groups 3 and 4 of previous classification schemes. These melt rocks are feldspathic, poor in incompatible and siderophile elements, and appear to have provenance in the Descartes formation to the east of the site. The Western trend (higher Sm Sc , Mg Fe , and Sm Yb ratios) consists of compositional groups 1 and 2. These relatively mafic, KREEP-bearing breccias are a major component (~35%) of the Cayley plains west of the site and are unusual, compared to otherwise similar melt breccias from other sites, in having high concentrations of Fe-Ni metal (1–2%). The metal is the carrier of the low-Ir/Au (~0.3 × chondritic) siderophile-element signature that is characteristic of the Apollo 16 site. Four compositionally distinct groups (1M, 1F, 2DB, and 2NR) of Western-trend melt breccias occur that are each represented by at least six samples. Compositional group 1 of previous classification schemes (the “poikilitic” or “LKFM” melt breccias) can be subdivided into two groups. Group 1M (represented by six samples, including 60315) is characterized by lower Al 2O 3 concentrations, higher MgO and alkali concentrations, and higher Mg Fe and Cr Sc ratios than group 1F (represented by fifteen samples, including 65015). Group 1M also has siderophile-element concentrations averaging about twice those of group 1F and Ir Au and Ir Ni ratios that are even lower than those of other Western-trend melt rocks ( Ir Au = 0.24 ± 0.03 , CI-normalized). At the mafic extreme of group 2 (“VHA” melt breccias), the melt lithology occurring as clasts in feldspathic fragmental breccias from North Ray crater (group 2NR) is compositionally distinct from the melt lithology of dimict breccias from the Cayley plains (group 2DB) in having higher concentrations of Sc, Cr, and heavy rare earth elements and lower concentrations of siderophile elements. The distinct siderophile-element signature (high absolute abundances, low Ir Au ratio) suggest that the four groups of mafic melt breccia are all somehow related. Ratios of some lithophile elements also suggest that they are more closely related to each other than they are to melt breccias from other Apollo sites. However, none of the breccia compositions can be related to any of the others by any simple process of igneous fractionation or mixing involving common lunar materials. Thus, the origin of the four groups of mafic melt breccia is enigmatic. If they were produced in only one or two impacts, then a mechanism exists for generating regimes of impact-melt breccia in a single impact that are substantially different from each other in composition. For various reasons, including the problem of delivering large volumes of four different types of melt to the Apollo 16 site, it is unlikely that any of these breccias were produced in basin-forming impacts. If they were produced in as many as four crater-forming impacts, then the unusual siderophile-element signature is difficult to explain. Possible explanations are 1. (1) the four groups of melt breccia all contain metal from a single, earlier impact, 2. (2) they were each formed by related metal-rich meteoroids, or 3. (3) some common postimpact process has resulted in metal of similar composition in each of four melt pools. Within a compositional group, most intrasample and intersample variation in lithophile element concentrations is caused by differences among samples in the proportion of a component of normative anorthosite or noritic anorthosite. In most cases, this compositional variation probably reflects variation in clast abundance. For group 2DB (and probably 2NR), differences in abundance of a component of ferroan anorthosite (estimated Al 2O 3 ≈ 32%) accounts for the compositional variation. For groups 1M and 1F, the anorthositic component is more mafic (estimated Al 2O 3 ≈ 26%). Some group-2 samples may be related by a troctolitic component of varying abundance.