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This study presents the results of high pressure and temperature experiments to investigate the mineral–melt trace element partitioning behaviour for minerals predicted to have formed during the crystallisation of the Lunar Magma Ocean (LMO). The focus of this work has been particularly on determining partition coefficients for parent–daughter pairs of radiogenic elements, for LMO-relevant temperatures, pressures and compositions. The new experimental data are compared with previous studies for the same minerals and elements in order to establish best estimates for the partition coefficient of each element for evolving compositions of minerals as predicted in recent studies modelling LMO crystallisation. These estimates are used to calculate evolving parent–daughter ratios in the LMO residual melt and crystallising minerals for the four main long-lived radiogenic isotope systems that have been studied in lunar samples (Rb–Sr, Sm–Nd, Lu–Hf and U–Pb). The calculated 87Rb/86Sr, 147Sm/144Nd, and 176Lu/177Hf ratios are consistent with predictions for the mantle sources of lunar basalts and evolved lithologies. In contrast, it is difficult to explain the wide range of 238U/204Pb source ratios predicted from the Pb isotopic compositions of basaltic lunar samples. Potential explanations for this observation are discussed, with the conclusion that the Moon most likely experienced a significant loss of volatiles (including Pb), towards the end of LMO crystallisation, resulting in the dramatic U–Pb fractionation evidenced by recent sample analyses.

Silicate-bearing iron meteorites record metal–silicate separation and mixing processes of planetesimals. Of particular interest is the IIE group as its silicate inclusions show great petrological diversity, probably resulting from the complex petrogenesis involving early differentiation and impact-induced dynamic mixing, re-melting, and reduction. These geologic records may have been documented by individual minerals to various extents, which blurs the chronological records on the formation of IIEs. Here, by combining X-ray elemental mapping with ion microprobe dating technique, we show that two groups of phosphates are present in the Weekeroo Station IIE iron meteorite. They have distinct petrography, mineralogy, Th/U ratios, and Pb isotopic compositions, which reflects their different formation mechanisms. One group (Group 1) has a fine-grained, euhedral or acicular habit, suggesting rapid crystallization from a melt during the metal–silicate mixing. By contrast, the other group (Group 2) is intimately associated with the decomposition and reduction of pyroxene under subsolidus conditions. The Group 1 phosphates yield a precise Pb–Pb age of 4528 ± 11 Ma and they provide the first robust constraint on the timing of impact-induced metal–silicate mixing on the IIE iron meteorite parent body. The Group 2 phosphates, on the other hand, probably record a Pb–Pb age at least 50 Myr younger, and they give insight into the role of subsequent impacts on the alteration of IIE irons. Combining our results with published chronological data suggests that the formation of IIEs irons is consistent with early partial differentiation followed by multiple impact-driven metal–silicate mixing and that most of them were not shielded from subsequent impacts.

Impact glasses found in lunar soils provide a possible window into the impact history of the inner solar system. However, their use for precise reconstruction of this history is limited by an incomplete understanding of the physical mechanisms responsible for their origin and distribution and possible relationships to local and regional geology. Here, we report U-Pb isotopic dates and chemical compositions of impact glasses from the Chang’e-5 soil and quantitative models of impact melt formation and ejection that account for the compositions of these glasses. The predominantly local provenance indicated by their compositions, which constrains transport distances to

LA-ICP-MS method was applied to investigate U-Pb and Lu-Hf isotope systematics of zircon crystals from charnockitic gneiss and biotite-garnet-hypersthene enderbite that occur in the lower reaches of the Yatran river (Yatran block of the Bouh river area). According to the obtained isotope data, charnockitic gneiss hosts three zircon populations. The oldest one is represented by three crystals that have isotope age between 3125 and 3300 Ma, and εHf values between –2.3 and –7.5. The next population is well-defined, it has an age of 2038±25 Ma and large variations of Hf isotope composition: 176Hf/177Hf — from 0.28122 to 0.28261, εHf — from –9.3 до 4.6. However, the ages of most of the analyzed zircons spread along the concordia between 2300 and 2800 Ma. All zircons in this population have a similar Hf isotope composition 176Hf/177Hf = 0.28072 to 0.28092, which does not depend on the age. It is characteristic that the oldest (with preserved U-Pb isotope systematics) crystals have positive or slightly negative εHf values. Most of the U-Pb isotope analyses of zircons from enderbite fall on the discordia line that has an upper interception age of 2029 ± 18 Ma. A small number of discordant grains have 207Pb/206Pb ages up to 2500 Ma. Hafnium isotope composition in zircons from enderbite varies widely: 176Hf/177Hf = 0.28131 to 0.28151, and εHf from –6.2 to 1.8.

Apollo 16 soil-like regolith breccia 65745,7 contains two zircon-bearing clasts. One of these clasts is a thermally annealed silica-rich rock, which mineralogically has affinities with the High Alkali Suite (Clast 1), and yields zircon dates ranging from 4.08 to 3.38 Ga. The other clast is a KREEP-rich impact melt breccia (Clast 2) and yields zircon dates ranging from 3.97 to 3.91 Ga. The crystalline cores of both grains, which yield dates ofca3.9 Ga, have undergone shock pressure modification at less than 20 GPa. We interpret that the U-Pb chronometer in these zircon grains has been partially reset by the Imbrium basin-forming event when the clasts were incorporated into the Cayley Plains ejecta blanket deposit. The zircon grains in Clast 1 have been partially decomposed, resulting in a breakdown polymineralic texture, with elevated U, Pb and Th abundances compared with those in the crystalline zircon. These decomposed areas exhibit younger dates around 3.4 Ga, suggesting a secondary high-pressure, high-temperature event, probably caused by an impact in the local Apollo 16 highlands area.

The triple oxygen isotope compositions of phosphate grains in six martian meteorites have been measured by Secondary Ion Mass Spectrometry (SIMS) and combined together with their chlorine isotope and halogen concentrations have been used to constrain hydrosphere-lithosphere interactions on Mars. These samples include three enriched shergottites (Zagami, Roberts Massif 04262 and Larkman Nunatak 12011), one depleted shergottite (Tissint), an orthopyroxenite (Allan Hills 84001), and a regolith breccia (Northwest Africa 7533). The phosphates measured here have a range in δ18O [(18O/16O)sample/(18O/16O)Standard-1] × 103] from +1.0 to +6.8‰ and could be a result of indigenous mantle values, mixing with martian water, or replacement reactions taking place on the surface of Mars. Three samples have a Δ17O [δ17O-1000(1 + δ18O /1000)0.528-1] in equilibrium with the martian mantle (ALH 84001, Tissint, and Zagami), while three samples (LAR 12011, RBT 04262, and NWA 7533) have an elevated positive Δ17O outside of analytical uncertainty of the martian fractionation line (MFL). The phosphates in the latter group also have positive and negative δ37Cl [(37Cl/35Cl)sample/(37Cl/35Cl)standard – 1] × 103] and enrichments in halogens not seen in the rest of the sample suite. Perchlorate formation on Earth fractionates Cl in both positive and negative directions and generates a correlated positive Δ17O. Further, perchlorate has been detected in wt% amounts on the martian surface. Thus, these results strongly suggest the presence of multiple Cl isotope reservoirs on the martian surface that have interacted with the samples studied here over the last ca. 2 Ga of geologic time. The weighted average of Δ17O measurements from phosphate grains (n = 13) in NWA 7533, which are the explicit result of exchange reactions on the martian surface, yields a statistically robust mean value of 1.39 ± 0.19‰ (2σ, MSWD = 1.5, p = 0.13). This value likely represents an accurate estimate for an oxidized surface reservoir on Mars.

The LA-ICP-MS method was applied to investigate U-Pb and Lu-Hf isotope systematics of zircon crystals from charnockitoids that crop out in the open pits near Chausove village, Pervomaisk district. The association of enderbite gneisses, mafic and ultramafic (pyroxenite) granulites and vein bodies of pink biotite granites occur in the open pits. Enderbites are rather heterogeneous, and their composition varies from leucocratic quartzite-like rocks to enderbite-diorite. The Pervomaisk open pit is located within charnockite massif. Our data indicates that the association of enderbites and charnockites crystallised at 2850-2760 Ma from juvenile material (Hf isotope composition in zircons from enderbite-diorite is 176Hf/177Hf = 0.280915 ± 12, εHf2850 = +2; from leucocratic charnockite 176Hf/177Hf = 0.280875 ± 12, εHf2760 = –1; and from charnockite 176Hf/177Hf = 0.280875 ± 12, εHf2760 = –1). These rocks represented the newly formed Meso-Neoarchean crust, in contrast to the reworked older continental crust. This association has experienced a significant transformation in Paleoproterozoic. The last stage of transformation was accompanied by crystallisation of a new generation of zircon and formation of monazite at 2.04-2.06 Ga.

Significance We discovered a zircon record in a Martian meteorite that spans 4.2 Gyr, nearly the entire geologic history of Mars. Ancient zircons define a bimodal distribution with groupings at 4474 ± 10 Ma and 4442 ± 17 Ma, reflecting intense bombardment episodes triggered by the migration of the gas giant planets. A group of younger detrital zircons record ages from 1548.0 ± 8.8 Ma to 299.5 ± 0.6 Ma. The only plausible sources for these grains are the Elysium and Tharsis volcanic provinces that are the expressions of deep-seated mantle plumes. The chondritic-like Hf-isotope compositions of these zircons require the existence of a primitive and convecting mantle reservoir. Thus, these grains provide a tangible record of the deep Martian interior., Combining U–Pb ages with Lu–Hf data in zircon provides insights into the magmatic history of rocky planets. The Northwest Africa (NWA) 7034/7533 meteorites are samples of the southern highlands of Mars containing zircon with ages as old as 4476.3 ± 0.9 Ma, interpreted to reflect reworking of the primordial Martian crust by impacts. We extracted a statistically significant zircon population (n = 57) from NWA 7533 that defines a temporal record spanning 4.2 Gyr. Ancient zircons record ages from 4485.5 ± 2.2 Ma to 4331.0 ± 1.4 Ma, defining a bimodal distribution with groupings at 4474 ± 10 Ma and 4442 ± 17 Ma. We interpret these to represent intense bombardment episodes at the planet’s surface, possibly triggered by the early migration of gas giant planets. The unradiogenic initial Hf-isotope composition of these zircons establishes that Mars’s igneous activity prior to ∼4.3 Ga was limited to impact-related reworking of a chemically enriched, primordial crust. A group of younger detrital zircons record ages from 1548.0 ± 8.8 Ma to 299.5 ± 0.6 Ma. The only plausible sources for these grains are the temporally associated Elysium and Tharsis volcanic provinces that are the expressions of deep-seated mantle plumes. The chondritic-like Hf-isotope compositions of these zircons require the existence of a primitive and convecting mantle reservoir, indicating that Mars has been in a stagnant-lid tectonic regime for most of its history. Our results imply that zircon is ubiquitous on the Martian surface, providing a faithful record of the planet’s magmatic history.

The lunar cratering record is used to constrain the bombardment history of both the Earth and the Moon. However, it is suggested from different perspectives, including impact crater dating, asteroid dynamics, lunar samples, impact basin-forming simulations, and lunar evolution modelling, that the Moon could be missing evidence of its earliest cratering record. Here we report that impact basins formed during the lunar magma ocean solidification should have produced different crater morphologies in comparison to later epochs. A low viscosity layer, mimicking a melt layer, between the crust and mantle could cause the entire impact basin size range to be susceptible to immediate and extreme crustal relaxation forming almost unidentifiable topographic and crustal thickness signatures. Lunar basins formed while the lunar magma ocean was still solidifying may escape detection, which is agreeing with studies that suggest a higher impact flux than previously thought in the earliest epoch of Earth-Moon evolution., Lunar impact basins formed during the magma ocean solidification should have formed almost unidentifiable topographic and crustal thickness signatures, thus may escape detection. This result allows for a higher impact flux in the earliest epoch of Earth-Moon evolution.

The limited preservation of ancient crustal material poses a challenge for understanding the composition of Earth’s early crust. As a result of poor preservation and near-ubiquitous overprinting by later geological events, deciphering the early evolution of our planet often relies on the isotopic composition of resistive minerals, such as zircon. Although the isotopic information recorded by zircon grains has proved an invaluable asset to workers seeking to understand the geological evolution of the Earth, it is limited by the range of elements easily incorporated into the structure of the mineral. One way to overcome these limitations is by analysing inclusions of other minerals that were trapped within the zircon during crystallisation. Apatite has great potential in this respect, as it is commonly found as inclusions in magmatic zircon and records a variety of useful isotopic information. Here we present an approach for investigating igneous petrogenesis and crustal evolution by combining 87Sr/86Sr measurements of apatite inclusions with U–Pb and Hf isotope analysis of their host zircon crystal. The Sr isotope information contained in the apatite can be accessed by applying a novel SIMS technique we developed for this purpose. A case study applying this new approach to Eoarchean igneous rocks of the Narryer Terrane in the northern Yilgarn Craton of Western Australia demonstrates how this can be used to understand the evolution of this key locality, with implications for both regional geology and the growth of the continental crust.

Previous isotope studies of lunar samples have demonstrated that volatile loss was an important part of the early history of the Moon. The radiogenic U-Pb system, where Pb has a significantly lower T50% condensation temperature than U, has the capacity to both recognize and calibrate the extent of volatile loss but this approach has been hindered by terrestrial Pb contamination of samples. We employ a novel method that integrates analyses of individual samples by Ion Microprobe and Thermal Ionization mass spectrometry to correct for ubiquitous common Pb contamination, a method that results in significantly higher estimates for µ-values (238U/204Pb) than previously reported. Using this method, six of seven samples of low-Ti basaltic meteorites return µ-values between 1900 and 9600, values that are consistent with a re-evaluation of published results that return µ-values of 510–2900 for both low- and high-Ti basalts. While some degree of fractionation during partial melting may increase µ-values, we infer that the source region(s) for the basalts must also have had elevated µ-values by the time the lunar magma ocean solidified. Models to account for the available initial Pb isotopic compositions of lunar basalts in light of timing constraints from thermal modelling imply that their source regions had a µ-value of at least 280, consistent with the elevated µ-values of lunar basalts and that inferred for their sources. Such high µ-values are attributed to the preferential loss of more than 99% of the Pb over U relative to a precursor with a Mars-like composition in the aftermath of the giant impact. Such an extensive loss of Pb is consistent with previously reported losses of other elements with comparable volatility, namely Zn, Rb, Ga and CrO2. Finally, our modelling of highly-radiogenic lunar Pb isotopes assuming crystallization of the lunar magma ocean over 10′s of millions of years shows that the elevated µ-values allows for, but does not require, a young Moon formation age.

Glass beads formed by ejection of impact-melted lunar rocks and soils are an important component of lunar soils. These glasses range from 100s of microns to up to a few cm in diameter and contain variable, but usually relatively low (several hundred ppb to a few ppm), quantities of U. Because Pb is a volatile element, it tends to be lost from the melts, so individual impact glasses can be dated by the U-Th-Pb isotopic systems. The presence of two additional Pb components in lunar glasses, likely linked to addition of lunar Pb to the beads during their residence on the lunar surface and from terrestrial laboratory contamination, require corrections to the data before accurate formation ages of the glasses can be determined. Here we report a U-Th-Pb isotopic and geochemical study of impact glasses from the Apollo 14 soil 14163, which documents multiple impacts into chemically diverse targets that can be linked to the main groups of rocks found on the Moon, i.e., mare basalts, highlands plagioclase-rich rocks, and KREEP (from high contents of K, REE and P) enriched rocks. The impact ages show a bimodal distribution with peaks at ~3500-3700 Ma and < 1000 Ma, similar to that obtained previously by Ar-40-Ar-39 dating of other suites of lunar regolith glasses. Our data suggest two predominant age peaks at ~100 Ma and ~500 Ma, with other statistically definable clusters of ages also possible. As Pb is relatively resistant to subsolidus diffusive loss in these glasses, the age clusters probably represent primary formation ages during impact events, although processes such as preferential preservation of young glasses and impact conditions necessary for production of regolith glasses need further quantification. (C) 2021 The Authors. Published by Elsevier Ltd.

Funding: TEJ acknowledges support from the State Key Laboratory for Geological Processes and Mineral Resources, China University of Geosciences, Wuhan (Open Fund GPMR201903 ). We thank J. B. Balta and T. Prissel for their challenging reviews that led to significant improvements in the final version. Despite some 50 years of intense research on samples returned from the Apollo missions and lunar meteorites, along with remote-sensing and Earth-based observations, many questions regarding the formation and evolution of the Moon persist. These include the detailed compositional and density structure of the lunar mantle and the source and petrogenesis of the diverse suite of extrusive and intrusive igneous rocks. There is broad agreement that the primary internal structure of the Moon reflects crystallisation of a lunar magma ocean (LMO), and that an inverted density gradient within the mantle cumulates led to some reorganisation of layers by partial convective overturn. Experimental studies have provided invaluable constraints on crystallisation of the LMO, but are limited by the relatively small number of experiments that can practically be undertaken. Here we use recently-developed thermodynamic models for minerals and melt in the K2O–Na2O–CaO–FeO–MgO–Al2O3–SiO2–TiO2–Cr2O3 system to model crystallisation of a full-moon LMO based on two existing end-member bulk compositions—Taylor Whole-Moon (TWM), and Lunar Primitive Upper Mantle, LPUM—on which many experimental studies have been based. We follow several recent studies in considering equilibrium crystallisation of the first 50 vol.% and fractional crystallisation thereafter. Our results match well with experimental studies, and provide detailed constraints on the major oxide composition, mineralogy and density structure based on the two starting compositions that, while exhibiting some similarities, show important differences. The more fertile TWM composition contains significant quantities of garnet in the deep mantle, whereas the LPUM composition has none. By contrast, prior to any gravitational overturn, the uppermost mantle cumulates for TWM are strongly silica-undersaturated and contain abundant aluminous spinel, whereas those for LPUM are silica-saturated. For both starting compositions, with the exception of TiO2 and Na2O, our modelled compositions of the final dregs of fractionated melt show a reasonable match with existing estimates on the composition of urKREEP. Modelled partial melts of the upper-mantle cumulates at low to moderate melt fractions have major oxide compositions that match well with low- and intermediate-Ti lunar basalts. The correspondence is particularly good for picritic (green) glasses that likely represent melts derived from deeper levels within the upper mantle. The wide spread in TiO2 concentrations in lunar basalts and basaltic glasses is consistent with density-driven reorganisation involving ilmenite. Our simulations provide thermodynamically-robust estimates of the compositional, mineralogical and density structure of the lunar interior that are unprecedented in their detail, and which provide the foundation for several lines of future research addressing the origin and secular evolution of the Moon. Postprint

The results of a laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb dating and a Hf isotope study of zircon crystals separated from small eclogite xenoliths found in Devonian kimberlites within the Prypyat horst, Ukraine, have been reported. The studied area is located in the junction zone between the Sarmatian and Fennoscandian segments of the East European Platform. Four laser ablation sites on two zircon grains yielded Paleoproterozoic U–Pb ages between 1954 ± 24 and 1735 ± 54 Ma. In contrast, three of four Hf sites revealed negative εHf values and Paleoarchean to Mesoarchean model ages, excluding the possibility that the eclogite xenoliths represented segments of a juvenile Paleoproterozoic subducted slab or younger mafic melts crystallized in the subcontinental lithospheric mantle. A single laser ablation Hf spot yielded a positive εHf value (+3) and a Paleoproterozoic model age. Two models for eclogite origin can be proposed. The first foresees the extension of the Archean lower-crustal or lithospheric roots beneath the Sarmatia–Fennoscandia junction zone for over 200 km from the nearest known outcrop of Archean rocks in the Ukrainian Shield. The second model is that the Central Belarus Suture Zone represents a rifted-out fragment of the Kola–Karelian craton that was accreted to Sarmatia before the actual collision of these two segments of Baltica.

Sample return shows late lunar volcanism Measuring physical samples of Solar System bodies in the laboratory provides more information than is possible from remote sensing alone. In December 2020, the Chang’e-5 mission landed on the Moon, collected samples, and returned them to Earth. Che et al . analyze two fragments of volcanic lunar basalt collected by Chang’e-5. Radiometric dating using lead isotopes indicated that the rocks formed from magma that erupted about 2 billion years ago, later than other volcanic lunar samples. The abundance of extinct radioactive elements in the rock is too low for radioactive heating to have produced the magma. Another, thus far unknown, source must be responsible for the late lunar volcanism. —KTS

Orbital data indicate that the youngest volcanic units on the Moon are basalt lavas in Oceanus Procellarum, a region with high levels of the heat-producing elements potassium, thorium, and uranium. The Chang’e-5 mission collected samples of these young lunar basalts and returned them to Earth for laboratory analysis. We measure an age of 1963 ± 57 Ma for these lavas and determine their chemical and mineralogical compositions. This age constrains the lunar impact chronology of the inner Solar System and the thermal evolution of the Moon. There is no evidence for high concentrations of heat-producing elements in the deep mantle of the Moon that generated these lavas, so alternate explanations are required for the longevity of lunar magmatism.

The results of an LA-ICP-MS U-Pb dating and Hf isotope study of zircon crystals separated from small eclogite xenoliths found in Devonian kimberlites within the Prypyat horst, Ukraine, are reported. The studied area is located in the Central Belarusian Suture Zone, which represents a Paleoproterozoic belt extending along the boundary between the Sarmatian and Fennoscandian segments of the East European Platform. Four laser ablation sites on two zircon grains yielded Paleoproterozoic U-Pb ages between 1954 ± 24 Ma and 1735 ± 54 Ma. In contrast, three of four Hf sites revealed negative εHf values and Paleoarchean to Mesoarchean model ages, excluding the possibility that the eclogite xenoliths represent segments of a Paleoproterozoic subducted slab or younger mafic melts crystallized in the subcontinental lithospheric mantle. A single laser ablation Hf spot yielded a positive εHf value (+3) and a Paleoproterozoic model age. Two models for eclogite origin can be proposed. The first foresees the extension of the Archean lower-crustal or lithospheric roots beneath the Central Belarus Suture Zone for over 200 km from the nearest known outcrop of Archean rocks. The second model is that the Central Belarus Suture Zone represents a rifted-out fragment of the Kola-Karelian craton that was accreted to Sarmatia before the actual collision of these two segments of Baltica.

Precise crystallisation ages have been determined for a range of Apollo basalts from Pb-Pb isochrons generated using Secondary Ion Mass Spectrometry (SIMS) analyses of multiple accessory phases including K-feldspar, K-rich glass and phosphates. The samples analysed in this study include five Apollo 11 high-Ti basalts, one Apollo 14 high-Al basalt, seven Apollo 15 low-Ti basalts, and five Apollo 17 high-Ti basalts. Together with the samples analysed in two previous similar studies, Pb-Pb isochron ages have been determined for all of the major basaltic suites sampled during the Apollo missions. The accuracy of these ages has been assessed as part of a thorough review of existing age determinations for Apollo basalts, which reveals a good agreement with previous studies of the same samples, as well as with average ages that have been calculated for the emplacement of the different basaltic suites at the Apollo landing sites. Furthermore, the precision of the new age determinations helps to resolve distinctions between the ages of different basaltic suites in more detail than was previously possible. The proposed ages for the basaltic surface flows at the Apollo landing sites have been reviewed in light of these new sample ages. Finally, the data presented here have also been used to constrain the initial Pb isotopic compositions of the mare basalts, which indicate a significant degree of heterogeneity in the lunar mantle source regions, even among the basalts collected at individual landing sites.

U-Pb ages of zircon in four different Apollo 14 breccias (14305, 14306, 14314, and 14321) were obtained by secondary ion mass spectrometry. Some of the analyzed grains occur as cogenetic, poikilitic zircon grains in lithic clasts, revealing magmatic events at ~4286 Ma, ~4200–4220 Ma, and ~4150 Ma. The age distribution of the crystal clasts in the breccias exhibits a minor peak at ~4210 Ma, which can be attributed to a magmatic event, as recorded in zircon grains located in noritic clasts. An age peak at ~4335 Ma is present in all four breccias, as well as zircon grains from different Apollo landing sites, enhancing the confidence that these grains recorded a global zircon-forming event. The overall age distribution among the four breccias exhibits minor differences between the breccias collected farther away from the Cone Crater and the ones collected within the continuous ejecta blanket of the Cone Crater. A granular zircon grain yielded a 207Pb/206Pb age of 3936 ± 8 Ma, which is interpreted as an impact event. A similar age of 3941 ± 5 Ma (n = 17, MSWD = 0.89, P = 0.58) was obtained for a large zircon grain (~430 × 340 μm in size). This grain might have crystallized in the same impact melt sheet which formed the granular zircon or the age is representative of the final extrusion of KREEP magma. The majority of zircon grains, however, occur as isolated crystal clasts within the matrix and their ages cannot be correlated with any real events (impact or magmatic) nor can the possibility be excluded that these ages represent partial resetting of the U-Pb system.

Miller Range (MIL) 13317 is a heterogeneous basalt-bearing lunar regolith breccia that provides insights into the early magmatic history of the Moon. MIL 13317 is formed from a mixture of material with clasts having an affinity to Apollo ferroan anorthosites and basaltic volcanic rocks. Noble gas data indicate that MIL 13317 was consolidated into a breccia between 2610 ± 780 Ma and 1570 ± 470 Ma where it experienced a complex near-surface irradiation history for ~835 ± 84 Myr, at an average depth of ~30 cm. The fusion crust has an intermediate composition (Al2O3 15.9 wt%; FeO 12.3 wt%) with an added incompatible trace element (Th 5.4 ppm) chemical component. Taking the fusion crust to be indicative of the bulk sample composition, this implies that MIL 13317 originated from a regolith that is associated with a mare-highland boundary that is KREEP-rich (i.e., K, rare earth elements, and P). A comparison of bulk chemical data from MIL 13317 with remote sensing data from the Lunar Prospector orbiter suggests that MIL 13317 likely originated from the northwest region of Oceanus Procellarum, east of Mare Nubium, or at the eastern edge of Mare Frigoris. All these potential source areas are on the near side of the Moon, indicating a close association with the Procellarum KREEP Terrane. Basalt clasts in MIL 13317 are from a very low-Ti to low-Ti (between 0.14 and 0.32 wt%) source region. The similar mineral fractionation trends of the different basalt clasts in the sample suggest they are comagmatic in origin. Zircon-bearing phases and Ca-phosphate grains in basalt clasts and matrix grains yield 207Pb/206Pb ages between 4344 ± 4 and 4333 ± 5 Ma. These ancient 207Pb/206Pb ages indicate that the meteorite has sampled a range of Pre-Nectarian volcanic rocks that are poorly represented in the Apollo, Luna, and lunar meteorite collections. As such, MIL 13317 adds to the growing evidence that basaltic volcanic activity on the Moon started as early as ~4340 Ma, before the main period of lunar mare basalt volcanism at ~3850 Ma.

International audience; Large impact structures with peak rings are common landforms across the solar system, and their formation has implications for both the interior structure and thermal evolution of planetary bodies. Numerical modeling and structural studies have been used to simulate and ground truth peak-ring formative mechanisms, but the shock metamorphic record of minerals within these structures remains to be ascertained. We investigated impact-related microstructures and high-pressure phases in zircon from melt-bearing breccias, impact melt rock, and granitoid basement from the Chicxulub peak ring (Yucatán Peninsula, Mexico), sampled by the International Ocean Discovery Program (IODP)/International Continental Drilling Project (IODP-ICDP) Expedition 364 Hole M0077A. Zircon grains exhibit shock features such as reidite, zircon twins, and granular zircon including “former reidite in granular neoblastic” (FRIGN) zircon. These features record an initial high-pressure shock wave (>30 GPa), subsequent relaxation during the passage of the rarefaction wave, and a final heating and annealing stage. Our observed grain-scale deformation history agrees well with the stress fields predicted by the dynamic collapse model, as the central uplift collapsed downward-then-outward to form the peak ring. The occurrence of reidite in a large impact basin on Earth represents the first such discovery, preserved due to its separation from impact melt and rapid cooling by the resurging ocean. The coexistence of reidite and FRIGN zircon within the impact melt–bearing breccias indicates that cooling by seawater was heterogeneous. Our results provide valuable information on when different shock microstructures form and how they are modified according to their position in the impact structure, and this study further improves on the use of shock barometry as a diagnostic tool in understanding the cratering process.

Since the Apollo 14 mission delivered samples of the Fra Mauro formation, interpreted as ejecta of the Imbrium impact, defining the age of this impact has emerged as one of the critical tasks required for the complete understanding of the asteroid bombardment history of the Moon and, by extension, the inner Solar System. Significant effort dedicated to this task has resulted in a substantial set of ages centered around 3.9 Ga and obtained for the samples from most Apollo landing sites using a variety of chronological methods. However, the available age data are scattered over a range of a few tens of millions of years, which hinders the ability to distinguish between the samples that are truly representative of the Imbrium impact and those formed/reset by other, broadly contemporaneous impact events. This study presents a new set of U-Pb ages obtained for the VHK (very high K) basalt clasts found in the Apollo 14 breccia sample 14305 and phosphates from (i) several fragments of impact-melt breccia extracted from Apollo 14 soil sample 14161, and (ii) two Apollo 15 breccias 15455 and 15445. The new data obtained for the Apollo 14 samples increase the number of independently dated samples from this landing site to ten. These Apollo 14 samples represent the Fra Mauro formation, which is traditionally viewed as Imbrium ejecta, and therefore should record the age of the Imbrium impact. Using the variance of ten ages, we propose an age of 3922 ± 12 Ma for this event. Samples that yield ages within these limits can be considered as possible products of the Imbrium impact, while those that fall significantly outside this range should be treated as representing different impact events. Comparison of this age for Imbrium (determined from Apollo 14 samples) with the ages of another eleven impact-melt breccia samples collected at four other landing sites and a related lunar meteorite suggests that they can be viewed as part of Imbrium ejecta. Comprehensive review of 40Ar/39Ar ages available for impact melt samples from different landing sites and obtained using the step-heating technique, suggests that the majority of the samples that gave robust plateau ages are indistinguishable within uncertainties and altogether yield a weighted average age of 3916 ± 7 Ma (95 % conf., MSWD = 1.1; P = 0.13) and a median average age of 3919 + 14/-12 Ma, both of which agree with the confidence interval obtained using the U-Pb system. These samples, dated by 40Ar/39Ar method, can be also viewed as representing the Imbrium impact. In total 36 out of 41 breccia samples from five landing sites can be interpreted to represent formation of the Imbrium basin, supporting the conclusion that Imbrium material was distributed widely across the near side of the Moon. Establishing temporal limits for the Imbrium impact allows discrimination of ten samples with Rb-Sr and 40Ar/39Ar ages about 50 Ma younger than 3922 ± 12 Ma. This group may represent a separate single impact on the Moon and needs to be investigated further to improve our understanding of lunar impact history.

The composition of Earth's early crust is challenging to assess as only a fragmented record remains. As a consequence, deciphering the composition of early crust as a means to understand early processes on our planet often relies on the isotopic composition of resistive minerals. Here we present a new tool for investigating igneous petrogenesis and crustal evolution by combining 87Sr/86Sr measurements of apatite inclusions with U–Pb and Hf isotope analysis of their host zircon crystals. This approach takes advantage of the complementary inverse fractionation behaviour of Rb/Sr and Lu/Hf, and the cogenetic host/inclusion relationship, to link the three isotopic systems and construct an evolution model in triple isotope space. By applying this triple isotope system modelling to Mesoarchean igneous rocks from the Akia terrane in SW Greenland, we reconstruct a bulk SiO2 composition of 63-68 wt% for the precursor source crust and infer an average crustal residence time of 300–350 Ma. Our modelling implicates involvement of intermediate to felsic Paleo-Eoarchean crust in the genesis of voluminous 3.0 Ga magmatic rocks of the Akia terrane, one of the largest components of the Archean North Atlantic Craton. A further outcome of this approach is the ability to place more robust empirical constraints on the Lu/Hf ratio of the precursor crust by comparison of the modelling output to a global whole-rock dataset. The approach in this work provides a template for further application to ancient rocks in order to better understand the evolution of early Earth.

Constraining the duration of magmatic activity on the Moon is essential to understand how the lunar mantle evolved chemically through time. Determining age and initial isotopic compositions of mafic lunar meteorites is a critical step in defining the periods of magmatic activity that occurred during the history of the Moon and to constrain the chemical characteristics of mantle components involved in the sources of the magmas. We have used the in situ Pb-Pb SIMS technique to investigate eight lunar gabbros and basalts, including six meteorites from the Northwest Africa (NWA) 773 clan (NWA 2727, NWA 2700, NWA 3333, NWA 2977, NWA 773, and NWA 3170), NWA 4734, and Dhofar 287A. These samples have been selected as there is no clear agreement on their age and they are all from the dominant low titanium chemical group. We have obtained ages of 2981 +/- 12 Ma for NWA 4734 and 3208 +/- 22 Ma for Dhofar 287. For the NWA 773 clan, four samples (the fine-grained basalt NWA 2727 and the three gabbros NWA 773, NWA 2977, NWA 3170) out of six yielded isochron-calculated ages that are identical within uncertainties and yielding an average age of 3086 +/- 5 Ma. The age obtained for the fine-grained basalt NWA 2700 is not precise enough for comparison with the other samples. The gabbroic sample NWA 3333 yielded an age of 3038 +/- 20 Ma suggesting that two distinct magmatic events may be recorded in the meteorites of the NWA 773 clan. The present study aims to identify and assess all potential issues that are associated with different ways to date lunar rocks using U-Pb-based methods. To achieve this, we have compared the new ages with the previously published data set. The entire age data set from lunar mafic meteorites was also screened to identify data showing analytical issues and evidence of resetting and terrestrial contamination. The data set combining the ages of mafic lunar meteorites and Apollo rocks suggests pulses of magmatic activity with two distinct phases between 3950 and 3575 Ma and between 3375 and 3075 Ma with the two phases separated by a gap of approximately 200 Ma. The evolution of the Pb initial ratios of the low-Ti mare basalts between approximately 3400 and 3100 Ma suggests that these rocks were progressively contaminated by a KREEP-like component.

Constraining the duration of magmatic activity on the Moon is essential to understand how the lunar mantle evolved chemically through time. Determining age and initial isotopic compositions of mafic lunar meteorites is a critical step in defining the periods of magmatic activity that occurred during the history of the Moon and to constrain the chemical characteristics of mantle components involved in the sources of the magmas.We have used the in-situ Pb–Pb SIMS technique to investigate lunar gabbros and basalts, including meteorites from the Northwest Africa (NWA) 773 clan (NWA 2727, NWA 3333, NWA 2977, NWA 773 and NWA 3170), LAP 02224, NWA 4734 and Dhofar 287A. These samples have been selected as they all belong to the dominant chemical group of low-titanium mare basalts and there is no clear agreement on their age. We have obtained ages of 2978 ± 13 Ma for LAP02224, 2981 ± 12 Ma for NWA 4734 and 3208 ± 22 Ma for Dhofar 287. For the NWA 773 clan, four samples (NWA 2727, NWA 773, NWA 2977, NWA 3170) yielded isochron-calculated ages that are identical within uncertainties with an average age of 3086.1 ± 4.8 Ma. The gabbroic sample NWA 3333 yielded an age of 3038 ± 20 Ma suggesting that two distinct magmatic events are recorded in the meteorites of the NWA 773 clan.The entire age dataset from lunar mafic meteorites was screened to identify data that are problematic from an analytical viewpoint and/or show evidence of resetting and terrestrial contamination. This refined dataset combines the ages of mafic lunar meteorites and Apollo samples and suggests pulses in magmatic activity, with two main phases between 3350 and 3100 Ma and between 3900 and 3550 Ma followed by a minor phase at ~3000 Ma.The evolution of the Pb initial ratios of the low-Ti mare basalts between 3400 Ma and 3100 Ma suggests that these rocks were progressively contaminated by a KREEP-like component. Nevertheless, the ~3000 Ma mafic rocks (NWA4734 and LAP02224) show significant differences in terms of initial 204Pb/206Pb ratios that illustrates that the lunar mantle is probably more heterogeneous than has previously been assumed.

International audience; The sulfur isotope budget of Martian regolith breccia (NWA 7533) has been addressed from conventional fluorination bulk rock analyses and ion microprobe in situ analyses. The bulk rock analyses yield 865 ± 50 ppm S in agreement with LA‐ICP‐MS analyses. These new data support previous estimates of 80% S loss resulting from terrestrial weathering of NWA 7533 pyrite. Pyrite is by far the major S host. Apatite and Fe oxyhydroxides are negligible S carriers, as are the few tiny igneous pyrrhotite–pentlandite sulfide grains included in lithic clasts so far identified. A small nonzero Δ33S (−0.029 ± 0.010‰) signal is clearly resolved at the 2σ level in the bulk rock analyses, coupled with negative CDT‐normalized δ34S (−2.54 ± 0.10‰), and near‐zero Δ36S (0.002 ± 0.09‰). In situ analyses also yield negative Δ33S values (−0.05 to −0.30‰) with only a few positive Δ33S up to +0.38‰. The slight discrepancy compared to the bulk rock results is attributed to a possible sampling bias. The occurrence of mass‐independent fractionation (MIF) supports a model of NWA 7533 pyrite formation from surface sulfur that experienced photochemical reaction(s). The driving force that recycled crustal S in NWA 7533 lithologies—magmatic intrusions or impact‐induced heat—is presently unclear. However, in situ analyses also gave negative δ34S values (+1 to −5.8‰). Such negative values in the hydrothermal setting of NWA 7533 are reflective of hydrothermal sulfides precipitated from H2S/HS‐ aqueous fluid produced via open‐system thermochemical reduction of sulfates at high temperatures (>300 °C).

Despite the wide utility of apatite, Ca5(PO4)3(F,Cl,OH), in the geosciences, including tracing volatile abundances on the Moon and Mars, little is known about how the mineral responds to the extreme temperatures and pressures associated with hypervelocity impacts. To address this deficiency, we here present the first microstructural analysis and chemical mapping of shocked apatite from a terrestrial impact crater. Apatite grains from the Paasselkä impact structure, Finland, display intragrain crystal-plastic deformation as well as pervasive recrystallization—the first such report in terrestrial apatite. A partially recrystallized grain offers the opportunity to investigate the effect of shock recrystallization on the chemical composition of apatite. The recrystallized portion of the fluorapatite grain is depleted in Mg and Fe relative to the remnant non-recrystallized domain. Strikingly, the recrystallized region alone hosts inclusions of (Mg,Fe)2(PO4)F, wagnerite or a polymorph thereof. These are interpreted to be a product of phase separation during recrystallization and to be related to the reduced abundances of certain elements in the recrystallized domain. The shock-induced recrystallization of apatite, which we show to be related to changes in the mineral’s chemical composition, is not always readily visible in traditional imaging techniques (such as backscattered electron imaging of polished interior surfaces), thus highlighting the need for correlated microstructural, chemical, and isotopic studies of phosphates. This is particularly relevant for extraterrestrial phosphates that may have been exposed to impacts, and we urge the consideration of microstructural data in the interpretation of the primary or secondary nature of elemental abundances and isotopic compositions.

Supplementary data: Table 1 and Figures 1–8

A zircon population from an Archean tonalite sample from southern West Greenland has been used as a source analogue in order to test common methods and approaches applied to ancient detrital zircon populations. Measurements of U-Th-Pb, oxygen and Lu-Hf isotopes as well as rare earth element and Ti concentrations were made in these zircon crystals and, where possible, in multiple areas within a single grain. The population is dominated by oscillatory zoned cores aged 3.82 Ga with an isotopically and compositionally distinct rim that formed at 3.59 Ga. We demonstrate that multiple age components may be erroneously inferred from within these oscillatory zoned zircon cores, both from the total population and within individual grains. This has bearing on other zircon-hosted geochemical systems, as temporal correlations may be incorrectly assigned. Oxygen and Lu-Hf isotope compositions are relatively consistent through the population with only a small number of outliers. Ranges in rare earth element and Ti abundances are evident from the total population, from which apparent inverse cooling trends may be inferred. Additionally, we show that even with enhanced filtering of Ti concentrations using light rare earth element abundances, crystallisation temperatures derived from zircon grains of a single, hand sample sized rock can yield both wide and bimodal results. Since even simple, single “source rock” zircon populations may, without careful scrutiny, portray artificially complex results, particular care must be taken in the interpretation of complex ancient detrital zircon populations.

Breccia boulders scattered around the 25 Ma Cone Crater near the Apollo 14 landing site provide a potential source of material ejected from the underlying Fra Mauro formation, which is int ...

The U-Th-Pb isotopic data from detrital zircon grains from five samples of Archean quartzite from the Mt. Alfred area of the Illaara greenstone belt in the Yilgarn Craton of Western Australia are presented in this study. The zircon grains are typically fractured and contain both irregular and oscillatory zoned internal structures as revealed by cathodoluminescence imaging. Concordant 207Pb/206Pb ages range between 3109 ± 17 and 3918 ± 16 Ma (2σ), with three main age peaks at ca. 3640, 3690 and 3760 Ma. Older 207Pb/206Pb ages up to 4067 ± 5 Ma are strongly affected by at least one recent disturbance event, however one single-grain discordia yields an upper intercept age of 4107 ± 12 (MSWD = 1.2). A further sixteen zircon grains with multiple analyses define discordia that suggest U-Pb disturbance events in the Neoarchean and the Mesozoic, the latter as a result of invasive low temperature weathering solutions. The notable lack of grains with ages less than ∼3.6 Ga in the Mt. Alfred detrital zircon population differentiates it from other quartzite samples from both the Illaara Formation and the Eoarchean zircon-bearing metasedimentary rocks of the Narryer Terrane. Also, the limited spread of zircon ages between 3640 and 3760 Ma suggests a relatively uniform and possibly local source region. However, no rocks of this age have been found in the Youanmi Terrane. This implies either the distal transport of similarly aged clastic sediments at 3.1 Ga from the Narryer Gneiss Complex (NGC) to the Mt. Alfred area, or the previous existence of NGC-like rocks near the Illaara greenstone belt that are either not currently recognised or have since been destroyed.

The composition of Earth's early crust is challenging to assess as only a fragmented record remains. As a consequence, deciphering the composition of early crust as a means to understand early processes on our planet often relies on the isotopic composition of resistive minerals. Here we present a new tool for investigating igneous petrogenesis and crustal evolution by combining 87Sr/86Sr measurements of apatite inclusions with U–Pb and Hf isotope analysis of their host zircon crystals. This approach takes advantage of the complementary inverse fractionation behaviour of Rb/Sr and Lu/Hf, and the cogenetic host/inclusion relationship, to link the three isotopic systems and construct an evolution model in triple isotope space. By applying this triple isotope system modelling to Mesoarchean igneous rocks from the Akia terrane in SW Greenland, we reconstruct a bulk SiO2 composition of 63-68 wt% for the precursor source crust and infer an average crustal residence time of 300–350 Ma. Our modelling implicates involvement of intermediate to felsic Paleo-Eoarchean crust in the genesis of voluminous 3.0 Ga magmatic rocks of the Akia terrane, one of the largest components of the Archean North Atlantic Craton. A further outcome of this approach is the ability to place more robust empirical constraints on the Lu/Hf ratio of the precursor crust by comparison of the modelling output to a global whole-rock dataset. The approach in this work provides a template for further application to ancient rocks in order to better understand the evolution of early Earth.

Zircon megacrysts are commonly found in kimberlites and, together with olivine, low-Cr garnet, pyroxene, phlogopite, and ilmenite megacrysts, they constitute a mineral assemblage known as the “low-Cr suite”. The generally close similarity of ages and similar isotope geochemical characteristics of megacrysts and matrix minerals in the host kimberlites support a cognate origin. However, alteration rims commonly develop on zircon and ilmenite megacrysts, providing evidence for a lack of chemical equilibrium between the megacrysts and kimberlitic melts. Here, we report results of a detailed geochronological and geochemical study of zircon megacrysts found in the Middle Devonian Novolaspa kimberlite pipe and dyke located in the Azov Domain of the Ukrainian Shield. The concordia age of zircons is 397.0 ± 2.0 Ma, and it is 14 m.y. older than the age of kimberlite emplacement as defined by a Rb-Sr isochron on phlogopite. The average eHf(397) value for unaltered zircon megacrysts is 6.8 ± 0.14, with the alteration rims having similar Hf isotope systematics. These hafnium isotope data indicate a moderately depleted mantle source for zircon. Unaltered megacrystic zircons have low abundances of trace elements and fractionated REE, with pronounced positive Ce/Ce* anomalies and almost no Eu/Eu* anomalies. In contrast, alteration rims have very high and variable concentrations of trace elements, indicating a reaction between zircon and kimberlite melt. The melt or fluid responsible for zircon and ilmenite megacryst formation, in contrast to kimberlitic melt, was poor in incompatible trace elements, except for the HFSE (Zr, Hf, Nb, Ta, and Ti). The oxygen fugacity during crystallization of the megacryst suite was close to the FMQ buffer. Azov zircon megacrysts do not demonstrate close geochronological and isotope-geochemical similarities with their host kimberlites. They are cognate in the broad sense of being related to the same plume event, but their direct affinity is not clearly defined. The megacryst suite may have crystallized from the earliest melts/fluids that separated from the ascending mantle plume, whereas kimberlite magmas were emplaced 14 m.y. after this event.

Recent in situ Secondary Ion Mass Spectrometry (SIMS) Pb isotope analyses of lunar basalts have provided precise crystallisation ages and initial Pb isotopic compositions for these samples. In this study, the same approach has been tested in the Apollo 16 impact melt breccia 66095, referred to as the “Rusty Rock” due to its enrichments in volatile elements, including Pb. Based on these analyses of the breccia, a Pb-Pb isochron age of 3909±17 Ma (at the 95% confidence level) and an initial Pb composition for 66095 have been determined. This age is interpreted as representing the time of breccia formation that, when combined with recent studies of lunar breccias, can be linked to the Imbrium basin forming impact. The directly measured initial Pb composition of the breccia from this work is similar a modelled compositions presented previously, and likely reflects an average value for the lithologies present at the Apollo 16 landing site at the time that the Imbrium ejecta was emplaced. The 66095 initial Pb isotopic composition is compared with the compositions in other lunar samples and the nature of the endmember lithologies in this mixture has been discussed within the framework of a multiple stage model of Pb isotope evolution on the Moon. This study demonstrates the effectiveness of this technique beyond its application in crystalline basalts, opening up the possibility of obtaining precise geochronological and Pb isotopic compositions from a broader sample set than was previously recognised. GEO KAW Early Planetary Evolution

Water contents of the Martian mantle have previously been investigated using Martian meteorites, with several comprehensive studies estimating the water content in the parental melts and mantle source regions of the shergottites and Chassigny. However, no detailed studies have been performed on the Nakhla meteorite. One possible way to determine the water content of a crystallizing melt is to use the water content in nominally anhydrous minerals (NAMs) such as clinopyroxene and olivine. During or after eruption on the surface of a planetary body and during residence in a degassing magma, these minerals may dehydrate. By reversing this process experimentally, original (pre-dehydration) water concentrations can be quantified. In this study, hydrothermal rehydration experiments were performed at 2 kbar and 700 °C on potentially dehydrated Nakhla clinopyroxene crystals. Rehydrated clinopyroxene crystals exhibit water contents of 130 ± 26 (2σ) ppm and are thus similar to values observed in similar phenocrysts from terrestrial basalts. Utilizing clinopyroxene/melt partition coefficients, both the water content of the Nakhla parent melt and mantle source region were estimated. Despite previous assumptions of a relatively dry melt, the basaltic magma crystallizing Nakhla may have had up to 1.42 ± 0.28 (2σ) wt.% H 2 O. Based on an assumed low degree of partial melting, this estimate can be used to calculate a minimum estimate of the water content for Nakhla’s mantle source region of 72 ± 16 ppm. Combining this value with values determined for other SNC mantle sources, by alternative methods, gives an average mantle value of 102 ± 9 (2σ) ppm H 2 O for the Martian upper mantle throughout geologic time. This value is lower than the bulk water content of Earth’s upper mantle (∼250 ppm H 2 O) but similar to Earth’s MORB source (54–330 ppm, average ∼130 ppm H 2 O).

Secondary ion mass spectrometry (SIMS) U-Pb ages of Ca-phosphates from four texturally distinct breccia samples (72255, 76055, 76015, 76215) collected at the Apollo 17 landing site were obtained in an attempt to identify whether they represent a single or several impact event(s). The determined ages, combined with inferences from petrologic relationships, may indicate two or possibly three different impact events at 3920±3 Ma, 3922±5 Ma and 3930±5 Ma (all errors 2σ). Searching for possible sources of the breccias by calculating the continuous ejecta radii of impact basins and large craters as well as their expected ejecta thicknesses, we conclude that Nectaris, Crisium, Serenitatis and Imbrium are likely candidates. If the previous interpretation that the micropoikilitic breccias collected at the North Massif represent Serenitatis ejecta is correct, then the average 207Pb/206Pb age of 3930±5 Ma (2σ) dates the formation of the Serenitatis basin. The occurrence of zircon in the breccias sampled at the South Massif, which contain Ca-phosphates yielding an age of 3922±5 Ma (2σ), may indicate that the breccia originated from within the Procellarum KREEP terrane (PKT) and the Imbrium basin appears to be the only basin that could have sourced them. However, this interpretation implies that all basins suggested to fall stratigraphically between Serenitatis and Imbrium formed within a short (

In this paper, we compare the U-Pb zircon age distribution pattern of sample 14311 from the Apollo 14 landing site with those from other breccias collected at the same landing site. Zircons in breccia 14311 show major age peaks at 4340 and 4240 Ma and small peaks at 4110, 4030, and 3960 Ma. The zircon age patterns of breccia 14311 and other Apollo 14 breccias are statistically different suggesting a separate provenance and transportation history for these breccias. This interpretation is supported by different U-Pb Ca-phosphate and exposure ages for breccia 14311 (Ca-phosphate age: 3938 ± 4 Ma, exposure age: ~550–660 Ma) from the other Apollo 14 breccias (Ca-phosphate age: 3927 ± 2 Ma, compatible with the Imbrium impact, exposure age: ~25–30 Ma). Based on these observations, we consider two hypotheses for the origin and transportation history of sample 14311. (1) Breccia 14311 was formed in the Procellarum KREEP terrane by a 3938 Ma-old impact and deposited near the future site of the Imbrium basin. The breccia was integrated into the Fra Mauro Formation during the deposition of the Imbrium impact ejecta at 3927 Ma. The zircons were annealed by mare basalt flooding at 3400 Ma at Apollo 14 landing site. Eventually, at approximately 660 Ma, a small and local impact event excavated this sample and it has been at the surface of the Moon since this time. (2) Breccia 14311 was formed by a 3938 Ma-old impact. The location of the sample is not known at that time but at 3400 Ma, it was located nearby or buried by hot basaltic flows. It was transported from where it was deposited to the Apollo 14 landing site by an impact at approximately 660 Ma, possibly related to the formation of the Copernicus crater and has remained at the surface of the Moon since this event. This latter hypothesis is the simplest scenario for the formation and transportation history of the 14311 breccia. GEO KAW Early Planetary Evolution

Hypervelocity impact processes are uniquely capable of generating shock metamorphism, which causes mineralogical transformations and deformation that register pressure (P) and temperature (T) conditions far beyond even the most extreme conditions created by terrestrial tectonics. The mineral zircon (ZrSiO4) responds to shock deformation in various ways, including crystal-plasticity, twinning, polymorphism (e.g., transformation to the isochemical mineral reidite), formation of granular texture, and dissociation to ZrO2 + SiO2, which provide robust thermobarometers that record different extreme conditions. The importance of understanding these material processes is two-fold. First, these processes can mobilize and redistribute trace elements, and thus be accompanied by variable degrees of resetting of the U-Pb system, which is significant for the use of zircon as a geochronometer. Second, some features described herein form exclusively during shock events and are diagnostic criteria that can be used to confirm the hypervelocity origin of suspected impact structures. We present new P-T diagrams showing the phase relations of ZrSiO4 polymorphs and associated dissociation products under extreme conditions using available empirical and theoretical constraints. We present case studies to illustrate zircon microstructures formed in extreme environments, and present electron backscatter diffraction data for grains from three impact structures (Mistastin Lake of Canada, Ries of Germany, and Acraman of Australia) that preserve different minerals and microstructures associated with different shock conditions. For each locality, we demonstrate how systematic crystallographic orientation relationships within and between minerals can be used in conjunction with the new phase diagrams to constrain the P-T history. We outline a conceptual framework for a zircon-based approach to ‘extreme thermobarometry’ that incorporates both direct observation of high-P and high-T phases, as well as inferences for the former existence of phases from orientation relationships in recrystallised products, a concept we refer to here as ‘phase heritage’. This new approach can be used to unravel the pressure-temperature history of zircon-bearing samples that have experienced extreme conditions, such as rocks that originated in the Earth's mantle, and those shocked during impact events on Earth and other planetary bodies.