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  • 1.
    Alexander, Louise
    et al.
    Birkbeck College, University of London, United Kingdom.
    Snape, Joshua
    Swedish Museum of Natural History, Department of Geology.
    Joy, Katherine
    University of Manchester, United Kingdom.
    Downes, Hilary
    Birkbeck College, University of London, United Kingdom.
    Crawford, Ian
    Birkbeck College, University of London, United Kingdom.
    An analysis of Apollo lunar soil samples 12070,889, 12030,187, and 12070,891: Basaltic diversity at the Apollo 12 landing site and implications for classification of small-sized lunar samples2016In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 51, p. 1654-1677Article in journal (Refereed)
    Abstract [en]

    Lunar mare basalts provide insights into the compositional diversity of the Moon's interior. Basalt fragments from the lunar regolith can potentially sample lava flows from regions of the Moon not previously visited, thus, increasing our understanding of lunar geological evolution. As part of a study of basaltic diversity at the Apollo 12 landing site, detailed petrological and geochemical data are provided here for 13 basaltic chips. In addition to bulk chemistry, we have analyzed the major, minor, and trace element chemistry of mineral phases which highlight differences between basalt groups. Where samples contain olivine, the equilibrium parent melt magnesium number (Mg#; atomic Mg/[Mg + Fe]) can be calculated to estimate parent melt composition. Ilmenite and plagioclase chemistry can also determine differences between basalt groups. We conclude that samples of approximately 1–2 mm in size can be categorized provided that appropriate mineral phases (olivine, plagioclase, and ilmenite) are present. Where samples are fine-grained (grain size <0.3 mm), a “paired samples t-test” can provide a statistical comparison between a particular sample and known lunar basalts. Of the fragments analyzed here, three are found to belong to each of the previously identified olivine and ilmenite basalt suites, four to the pigeonite basalt suite, one is an olivine cumulate, and two could not be categorized because of their coarse grain sizes and lack of appropriate mineral phases. Our approach introduces methods that can be used to investigate small sample sizes (i.e., fines) from future sample return missions to investigate lava flow diversity and petrological significance.

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  • 2. Bellucci, Jeremy
    et al.
    Whitehouse, Martin
    Nemchin, Alexander
    Regolith breccia Northwest Africa 7533: Mineralogy and petrology with implications for early Mars2016In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, p. 1-36Article in journal (Refereed)
  • 3. Curran, N. M.
    et al.
    Joy, K. H.
    Snape, J. F.
    Pernet-Fisher, J. F.
    Gilmour, J. D.
    Nemchin, A. A.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Burgess, R.
    The early geological history of the Moon inferred from ancient lunar meteorite Miller Range 133172019In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 54, no 7, p. 1401-1430Article in journal (Refereed)
    Abstract [en]

    Abstract 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.

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  • 4. Hewins, Rodger
    et al.
    Zanda, Bridget
    Humayun, Munir
    Nemchin, Alexander
    Lorand, Jean-Pierre
    Pont, Sylvain
    Deldique, Damien
    Bellucci, Jeremy
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Regolith breccia Northwest Africa 7533: Mineralogy and petrology with implications for early Mars2016In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, p. 1-36Article in journal (Refereed)
    Abstract [en]

    Northwest Africa 7533, a polymict Martian breccia, consists of fine-grained clast- laden melt particles and microcrystalline matrix. While both melt and matrix contain medium-grained noritic-monzonitic material and crystal clasts, the matrix also contains lithic clasts with zoned pigeonite and augite plus two feldspars, microbasaltic clasts, vitrophyric and microcrystalline spherules, and shards. The clast-laden melt rocks contain clump-like aggregates of orthopyroxene surrounded by aureoles of plagioclase. Some shards of vesicular melt rocks resemble the pyroxene-plagioclase clump-aureole structures. Submicron size matrix grains show some triple junctions, but most are irregular with high intergranular porosity. The noritic-monzonitic rocks contain exsolved pyroxenes and perthitic intergrowths, and cooled more slowly than rocks with zoned-pyroxene or fine grain size. Noritic material contains orthopyroxene or inverted pigeonite, augite, calcic to intermediate plagioclase, and chromite to Cr-bearing magnetite; monzonitic clasts contain augite, sodic plagioclase, K feldspar, Ti-bearing magnetite, ilmenite, chlorapatite, and zircon. These feldspathic rocks show similarities to some rocks at Gale Crater like Black Trout, Mara, and Jake M. The most magnesian orthopyroxene clasts are close to ALH 84001 orthopyroxene in composition. All these materials are enriched in siderophile elements, indicating impact melting and incorporation of a projectile component, except for Ni-poor pyroxene clasts which are from pristine rocks. Clast-laden melt rocks, spherules, shards, and siderophile element contents indicate formation of NWA 7533 as a regolith breccia. The zircons, mainly derived from monzonitic (melt) rocks, crystallized at 4.43 ` 0.03 Ga (Humayun et al. 2013) and a 147Sm-143Nd isochron for NWA 7034 yielding 4.42 ` 0.07 Ga (Nyquist et al. 2016) defines the crystallization age of all its igneous portions. The zircon from the monzonitic rocks has a higher D17O than other Martian meteorites explained in part by assimilation of regolith materials enriched during surface alteration (Nemchin et al. 2014). This record of protolith interaction with atmosphere- hydrosphere during regolith formation before melting demonstrates a thin atmosphere, a wet early surface environment on Mars, and an evolved crust likely to have contaminated younger extrusive rocks. The latest events recorded when the breccia was on Mars are resetting of apatite, much feldspar and some zircons at 1.35–1.4 Ga (Bellucci et al. 2015), and formation of Ni-bearing pyrite veins during or shortly after this disturbance (Lorand et al. 2015).

  • 5. Lorand, Jean-Pierre
    et al.
    Labidi, Jabrane
    Rollion-Bard, Claire
    Thomassot, Emilie
    Bellucci, Jeremy J.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Nemchin, Alexander
    Humayun, Munir
    Farquhar, James
    Hewins, Roger H.
    Zanda, Brigitte
    Pont, Sylvain
    The sulfur budget and sulfur isotopic composition of Martian regolith breccia NWA 75332020In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 55, no 9, p. 2097-2116Article in journal (Refereed)
    Abstract [en]

    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 delta-33S (-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 permil) and near-zero delta-36S (0.002 ± 0.09 permil). In situ analyses also yield negative delta-33S values (-0.05 to -0.30 permil) with only a few positive delta-33S up to +0.38 permil. 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 permil). 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).

  • 6.
    merle, renaud
    Swedish Museum of Natural History.
    Annealing history of zircons from Apollo 14083 and 14303 impact breccias2018In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100Article in journal (Refereed)
  • 7.
    Merle, Renaud E.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Nemchin, A. A.
    Grange, M. L.
    Whitehouse, M. J.
    Pidgeon, R. T.
    High resolution U-Pb ages of Ca-phosphates in Apollo 14 breccias: Implications for the age of the Imbrium impact2014In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 49, no 12, p. 2241-2251Article in journal (Refereed)
    Abstract [en]

    Abstract Previous age estimates of the Imbrium impact range from 3770 to 3920 Ma, with the latter being the most commonly accepted age of this basin-forming event. The occurrence of Ca-phosphates in Apollo 14 breccias, interpreted to represent ejecta formed by this impact, provides a new opportunity to date the Imbrium event as well as refining the impact history of the Moon. We present new precise U-Pb analyses of Ca-phosphates from impact breccia sample 14311 that are concordant and give a reliable weighted average age of 3938 ± 4 Ma (2σ). Comparison with previously published U-Pb data on phosphate from Apollo 14 samples indicate that all ages are statistically similar and suggest phosphates could have been formed by the same impact at 3934 Ma ± 3 Ma (2σ). However, this age is older than the 3770 to 3920 Ma range determined for other samples and also interpreted as formed during the Imbrium impact. This suggests that several impacts occurred during a 20?30 Ma period around 3900 Ma and formed breccias sampled by the Apollo missions.

  • 8.
    Merle, Renaud E.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Nemchin, A. A.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Snape, J. F.
    Kenny, G. G.
    Swedish Museum of Natural History, Department of Geology.
    Bellucci, J. J.
    Connelly, J. N.
    Bizzarro, M.
    Pb-Pb ages and initial Pb isotopic composition of lunar meteorites: NWA 773 clan, NWA 4734, and Dhofar 2872020In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 55, no 8Article in journal (Refereed)
    Abstract [en]

    Abstract 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.

  • 9.
    Merle, Renaud
    et al.
    Curtin University.
    Nemchin, Alexander
    Curtin University.
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Pidgeon, Robert
    Curtin University.
    Grange, Marion
    Curtin University.
    Snape, Joshua
    Swedish Museum of Natural History, Department of Geology.
    Thiessen, Fiona
    Swedish Museum of Natural History, Department of Geology.
    Origin and transportation history of lunar breccia 143112017In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 52, no 5, p. 842-858Article in journal (Refereed)
    Abstract [en]

    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.

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  • 10. Pidgeon, R. T.
    et al.
    Merle, Renaud E.
    Swedish Museum of Natural History, Department of Geology.
    Grange, M. L.
    Nemchin, A. A.
    Whitehouse, M. J.
    Swedish Museum of Natural History, Department of Geology.
    Annealing of radiation damage in zircons from Apollo 14 impact breccia 14311: Implications for the thermal history of the breccia2016In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 51, no 1, p. 155-166Article in journal (Refereed)
    Abstract [en]

    Abstract Impact breccia 14311, was collected from the Apollo 14 landing site as a potential sample of the underlying Fra Mauro Formation. Published zircon U-Pb ages of >4000 Ma date the source material of the breccia and the apatite U-Pb age of ~3940 Ma is interpreted as dating thermal resetting of the apatite U-Pb systems. In this contribution we present new age information on the late stage thermal history of the breccia based on the annealing of radiation damage in the zircons. From Raman spectroscopic determination of the radiation damage within SIMS analytical spots on the zircons and the U and Th concentrations determined on these spots, we demonstrate that the radiation damage in the zircons has been annealed and we estimate the age of annealing at 3410 ± 80 Ma. This age is interpreted as a cooling age following heating of the breccia to above the annealing temperature of ~230 °C for stage 1 radiation damage in zircon, but below the temperature needed to reset the U-Pb system of apatite (~500 °C). It is proposed that this thermal event was associated with the prolonged period of Mare volcanism, from 3150 to 3750 Ma, that generated massive basalt flows in the vicinity of the sample location.

  • 11. Pidgeon, R. T.
    et al.
    Merle, Renaud
    Swedish Museum of Natural History, Department of Geology.
    Grange, M. L.
    Nemchin, A. A.
    Annealing history of zircons from Apollo 14083 and 14303 impact breccias2018In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 53, no 12, p. 2632-2643Article in journal (Refereed)
    Abstract [en]

    Abstract 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 interpreted to form from the ejecta blanket of the ~3.9 Ga Imbrium impact. However, questions remain as to whether all or some of the rocks collected are from the Fra Mauro Formation. In this contribution, we present new Raman measurements on zircons from impact breccias 14083 and 14303 that indicate a zircon radiation damage age of the breccias of 3900 ± 120 (2σ) Ma. These ages are compatible with a history of thermal shock during their emplacement as part of the Imbrium impact ejecta blanket. In contrast, previously published Raman analyses of zircons from a sample of breccia 14311 have a younger radiation damage age of 3410 ± 80 (2σ) Ma, confirming that this breccia had a different thermal history and was possibly unrelated to the Fra Mauro Formation. The radiation damage ages of breccias 14083 and 14303, in combination with previously published apatite U-Pb ages, place constraints on the thermal conditions within the Imbrium ejecta blanket.

  • 12.
    Plan, Anders
    et al.
    Department of Geology Lund University Sölvegatan 12 Lund 223 62 Sweden.
    Kenny, Gavin G.
    Swedish Museum of Natural History, Department of Geology.
    Erickson, Timmons M.
    Jacobs—JETS Astromaterials Research and Exploration Science Division NASA Johnson Space Center 2101 NASA Parkway Houston Texas 77058 USA.
    Lindgren, Paula
    Department of Geology Lund University Sölvegatan 12 Lund 223 62 Sweden.
    Alwmark, Carl
    Department of Geology Lund University Sölvegatan 12 Lund 223 62 Sweden.
    Holm‐Alwmark, Sanna
    Department of Geology Lund University Sölvegatan 12 Lund 223 62 Sweden;Niels Bohr Institute University of Copenhagen Copenhagen DK‐2100 Denmark;Natural History Museum Denmark University of Copenhagen Copenhagen DK‐2100 Denmark.
    Lambert, Philippe
    CIRIR—Center for International Research and Restitution on Impacts and on Rochechouart Sciences et Applications 218 Boulevard Albert 1er Bordeaux 33800 France.
    Scherstén, Anders
    Department of Geology Lund University Sölvegatan 12 Lund 223 62 Sweden.
    Söderlund, Ulf
    Department of Geology Lund University Sölvegatan 12 Lund 223 62 Sweden.
    Exceptional preservation of reidite in the Rochechouart impact structure, France: New insights into shock deformation and phase transition of zircon2021In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 56, no 10, p. 1795-1828Article in journal (Refereed)
    Abstract [en]

    Reidite, the high-pressure zircon (ZrSiO4) polymorph, is a diagnostic indicator of impact events. Natural records of reidite are, however, scarce, occurring mainly as micrometer-sized lamellae, granules, and dendrites. Here, we present a unique sequence of shocked zircon grains found within a clast from the Chassenon suevitic breccia (shock stageIII) from the ~200 Ma, 20–50 km wide Rochechouart impact structure in France. Our study comprises detailed characterization with scanning electron microscopy coupled with electron backscatter diffraction with the goal of investigating the stability and response of ZrSiO4 under extreme P–T conditions. The shocked zircon grains have preserved various amounts of reidite ranging from 4% up to complete conversion. The grains contain various variants of reidite, including the common habits: lamellae and granular reidite. In addition, three novel variants have been identified: blade, wedge, and massive domains. Several of these crosscut and offset each other, revealing that reidite can form at multiple stages during an impact event. Our data provide evidence that reidite can be preserved in impactites to a much greater extent than previously documented. We have further characterized reversion products of reidite in the form of fully recrystallized granular zircon grains and minute domains of granular zircon in reidite-bearing grains that occur in close relationship to reidite. Neoblasts in these grains have a distinct crystallography that is the result of systematic inheritance of reidite. We interpret that the fully granular grains have formed from prolonged exposure of temperatures in excess of 1200 °C. Reidite-bearing grains with granular domains might signify swift quenching from temperatures close to 1200 °C. Grains subjected to these specific conditions therefore underwent partial zircon-to-reidite reversion, instead of full grain recrystallization. Based on our ZrSiO4 microstructural constraints, we decipher the grains evolution at specific P–T conditions related to different impact stages, offering further understanding of the behavior of ZrSiO4 during shock.

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  • 13.
    Rider‐Stokes, B. G.
    et al.
    School of Physical Sciences The Open University Milton Keynes UK.
    Anand, M.
    School of Physical Sciences The Open University Milton Keynes UK;Department of Mineralogy The Natural History Museum London UK.
    White, L. F.
    School of Physical Sciences The Open University Milton Keynes UK.
    Darling, J. R.
    School of the Environment, Geography &amp; Geosciences University of Portsmouth Portsmouth UK.
    Tartèse, R.
    Department of Earth and Environmental Sciences The University of Manchester Manchester UK.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Franchi, I.
    School of Physical Sciences The Open University Milton Keynes UK.
    Greenwood, R. C.
    School of Physical Sciences The Open University Milton Keynes UK.
    Degli‐Alessandrini, G.
    School of Physical Sciences The Open University Milton Keynes UK.
    The impact history and prolonged magmatism of the angrite parent body2023In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100Article in journal (Refereed)
  • 14.
    Thiessen, Fiona
    Swedish Museum of Natural History, Department of Geology. Department of Geological Sciences, Stockholm University, SE-106 91, Stockholm, Sweden.
    Snape, Joshua
    Faculty of Earth and Life Sciences, VU Amsterdam, De Boelelaan 1085, 1081 HV, Amsterdam, the Netherlands.
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology. Department of Geological Sciences, Stockholm University, SE-106 91, Stockholm, Sweden.
    U-Pb SIMS ages of Apollo 14 zircon: Identifying distinct magmatic episodes2019In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 54, p. 1720-1736Article in journal (Refereed)
  • 15.
    Thiessen, Fiona
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Nemchin, Alexander
    Curtin University.
    Snape, Joshua
    Swedish Museum of Natural History, Department of Geology.
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Bellucci, Jeremy
    Swedish Museum of Natural History, Department of Geology.
    Impact history of the Apollo 17 landing site revealed by U-Pb SIMS ages2017In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 52, no 4, p. 584-611Article in journal (Refereed)
    Abstract [en]

    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 (<11 Ma) time interval, highlighting serious contradictions between global stratigraphic constraints, sample interpretation and chronological data. Alternatively, the slightly older age of the two micropoikilitic breccias may be a result of incomplete resetting of the U-Pb system preserved in some phosphate grains. Based on the currently available dataset this possibility cannot be excluded.

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    Impact history Apollo 17
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