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Shergottites have provided abundant information on the volcanic and impact history of Mars. Northwest Africa (NWA) 14672 contributes to both of these aspects. It is a vesicular ophitic depleted olivine–phyric shergottite, with average plagioclase An61Ab39Or0.2. It is highly ferroan, with pigeonite compositions En49‐25Fs41‐61Wo10‐14 like those of basaltic shergottites, for example, NWA 12335. Olivine (Fo53‐15) has discrete ferroan overgrowths, more ferroan when in contact with plagioclase than when enclosed by pyroxene. The pyroxene (a continuum of augite, subcalcic augite, and pigeonite) is patchy, with ragged "cores" enveloped or invaded by ferroan pyroxene. Magma mixing may be responsible for capture of olivine and formation of pyroxene mantles. The plagioclase is maskelynite‐like in appearance, but the original laths were (congruently) melted and the melt partly crystallized as fine dendrites. Most of the 14% vesicles occur within plagioclase. Olivine, pyroxene, and ilmenite occur in part as fine aggregates crystallized after congruent melting with limited subsequent liquid mixing. There are two fine‐grained melt components, barred plagioclase with interstitial Fe‐bearing phases, and glass with olivine dendrites, derived by melting of mainly plagioclase and mainly pyroxene, respectively. Rare silica particles contain coesite and/or quartz, and silica glass. The rock has experienced >50% melting, compatible with peak pressure >~65 GPa. It is the most highly shocked shergottite so far, at shock stage S6/7. It may belong to the group of depleted shergottites ejected at ~1 Myr from Tooting Crater. [ABSTRACT FROM AUTHOR]

Angrites are a small group of basaltic meteorites and their origin is currently disputed. Among these, Northwest Africa (NWA) 12774 is a quenched angrite that was reported having an anomalously high bulk Cr 2 O 3 content (∼0.45 wt%). However, the reason behind this anomaly, which is critical for understanding the evolution of the angrite parent body, remains unknown. Here, we performed a detailed petrographic, mineralogical, and bulk oxygen and chromium isotopic composition study on this meteorite. NWA 12774 consists of porous olivine macrocrysts, phenocrysts of olivine and Al-Ti-rich augite, and spinel micro-phenocrysts with fine-grained groundmass. The olivine macrocrysts and the magnesian cores of olivine phenocrysts show compositional correlations distinctly different from typical olivine phenocrysts. The olivine macrocrysts contain small chromite/chrome-spinel inclusions which have the highest Cr 2 O 3 content (53.2 wt%) for chromite/spinel in angrites to date. Based on these textural and chemical features, the olivine macrocrysts and the magnesian cores of olivine phenocrysts are identified as xenocrysts. Some pyroxene phenocrysts contain regions with complexly zoned microtextures, which have much larger chemical variations compared with those with simply zoned microtextures. The regions with complexly zoned microtextures are likely to be of xenocrystic origin. The bulk Cr 2 O 3 content in NWA 12774 was estimated through two approaches, both of which show the bulk Cr 2 O 3 content to be around 0.3 wt% or possibly up to ∼ 0.45 wt%, which is consistent with previously measured values. The high Cr 2 O 3 content in NWA 12774 could be attributed to both the high abundance of spinel micro-phenocrysts and their high Cr 2 O 3 contents, rather than the presence of Cr-rich xenocrysts. The calculated melt rare earth element concentration in NWA 12774 equilibrated with the most Mg-rich augite is essentially identical to those in LEW 87051 and Asuka 881371, which however have Cr 2 O 3 contents much lower than NWA 12774. We suggest that the mantle source of NWA 12774 may not be as depleted in Cr and probably other volatile elements as other angrite sources. The various Cr 2 O 3 contents in different quenched angrites probably reflect that their mantle sources have not been homogenized. [ABSTRACT FROM AUTHOR]

Northwest Africa (NWA) 13669 is a recently found nakhlite and here, we use 2‐D and 3‐D mineralogy and texture, quantitative textural analysis of pyroxene, bulk rock and mineral major and trace element compositions, and melt inclusion analyses to assess its formation and emplacement. Using these combined results, we determine that NWA 13669 is derived from a depleted mantle source common to nakhlites and modeled parental melt compositions from olivine‐ and pyroxene‐hosted melt inclusions record similar major element trends to other nakhlites, including an alkali enrichment. Homogeneous pyroxene and olivine and diffusive reequilibration of trace elements in melt inclusions provide evidence for magma storage in a crystal mush within the nakhlite plumbing system and suggest NWA 13669 has undergone extensive reequilibration. Quantitative textural analysis of NWA 13669, including crystal size distribution (CSD) profiles, CSD slope and intercepts, and residence times, are similar to the Yamato nakhlite group, and indicate that NWA 13669 likely experienced similar emplacement conditions. However, differences in bulk rock and mineral compositions suggest NWA 13669 represents a new flow or sill from a previously unsampled portion of the nakhlite igneous complex, further increasing the diversity of the nakhlite suite. [ABSTRACT FROM AUTHOR]

The Mg‐spinel‐bearing rocks are an essential component of the lunar crust. They are widely distributed on the Moon's near and far sides. The study of petrogenesis provides a rare opportunity to understand the early lunar crust‐mantle interaction. Northwest Africa 12279 is a unique Mg‐spinel‐bearing troctolitic anorthosite lunar meteorite that is unbrecciated and pristine. The modal content of the spinel‐bearing troctolitic component is ∼95%. Five hundred sixty spinels larger than 100 μm are investigated in this paper, and 38 of them are found to contain magma melt inclusions. These magma melt inclusions represent the mixed composition between mantle melt and crust material during the crystallization of a spinel. They generally show an immiscible liquid phase separation, which can be divided into a magnesium‐rich and silica‐rich phase. The former is similar in chemical composition to the lunar mantle's peridotite or plutonic ultramafic Mg‐suite. The mantle melt reacts successively with Ferroan Anorthosites in the crust to crystallize Mg‐spinel, plagioclase, olivine, pyroxene, and silica phases. The large grains of euhedral Mg‐spinels with homogeneous chemical composition indicate they are the products of equilibrium crystallization, while plagioclase, olivine, pyroxene, and silica phase are the products of differentiated crystallization of mixed magma. This reaction may represent a typical process of lunar Mg‐suite. This work is the first to find petrological evidence that the melt from the lunar mantle intrudes into the crust and then undergoes a liquid phase immiscible separation to form the Mg‐spinel‐bearing troctolitic anorthosite. Plain Language Summary: Northwest Africa 12279 (weight 1,830 g) is the only known pristine and unbrecciated lunar spinel‐bearing troctolitic anorthosite, including lunar meteorites and returned samples. These pristine samples are indispensable for understanding Moon's history and chemical evolution. The spinel‐bearing rocks are an essential component of the lunar crust. They are widely distributed on the Moon's near and far sides. The study of petrogenesis provides a rare opportunity to understand the early lunar crust‐mantle interaction. Five hundred sixty spinels larger than 100 μm are investigated in three polished thin sections, and 38 contained magma melt inclusions. These magmatic inclusions represent the mixed composition between early mantle melt and crust material during the crystallization of a spinel. This work is the first to find evidence that the melt from the lunar mantle intrudes into the crust. The magnesium‐rich melt from the mantle assimilates with ferroan anorthosite (an igneous rock is composed of >90 vol.% plagioclase rich in calcium with minor iron‐rich pyroxene and olivine) from the early crust to form an Mg‐spinel‐bearing hypabyssal igneous rock. Key Points: Northwest Africa (NWA) 12279 is a unique lunar meteorite that is both unbrecciated and pristineThe magmatic melt inclusion in Mg‐spinel represents the mixed composition between lunar mantle melt and anorthositic crustThe formation of Mg‐spinel in NWA 12279 results from the interaction between the mantle material and the anorthositic crust of the Moon [ABSTRACT FROM AUTHOR]

Northwest Africa (NWA) 8418 is an unusual chondrite whose properties do not exactly match those of any other known chondrite. It has similarities to the CV (Vigarano group), CK (Karoonda group), and CL (Loongana group) chondrites, but its abundance of large calcium‐aluminum‐rich inclusions (CAIs) and the low NiO content (<0.2 wt%) of its matrix olivine ally it most closely with the CV group. The absence of grossular, monticellite, wollastonite, and sodalite from the alteration products of the CAIs; the magnesium‐rich nature of the matrix olivines (Fa38) relative to that of the CV3 chondrites (~Fa50); and the presence of secondary Na‐bearing plagioclase and chlorapatite indicate a metamorphic temperature >600 °C. NWA 8418 contains kamacite, taenite, and troilite, and lacks magnetite and pentlandite. We propose that NWA 8418 be reclassified as a reduced CV4 chondrite, which makes it the first CV chondrite of petrologic type 4. [ABSTRACT FROM AUTHOR]

Northwest Africa (NWA) 7203 is a quenched angrite, showing mineralogical features typically not present in other quenched angrites. NWA 7203 exhibits textures whose grain size varies from fine grains (<10 μm) to coarse grains (~3 mm), while other quenched angrites show only single‐sized textures. Fine‐grained and coarse‐grained lithologies have nearly the same bulk compositions. Cooling rates were estimated to be ~80 °C h−1 for fine‐grained lithologies and ~1 °C h−1 for coarse‐grained lithologies. Mg‐rich olivines (~Fo64) were found only in fine‐grained lithologies. Crystallization of NWA 7203 started in the fine‐grained lithologies with Mg‐rich olivine grains acting as seeds for crystallization. Coarse‐grained lithologies were subsequently formed under conditions of slower cooling. NWA 7203 shows clear shock metamorphic textures unlike other quenched angrites except for NWA 1670. We confirm that the oxygen isotopic ratios of NWA 7203 plot on the angrite fractionation line within uncertainty. However, the obtained Pb‐Pb age of NWA 7203 is 4543 ± 19 Ma, younger than the ages of other quenched angrites, which might be a result of disturbance by shock metamorphism. The finding of shock metamorphism of NWA 7203 suggests that some angrites might be derived from asteroids that remained large (>10 km in diameter) during the late heavy bombardment. [ABSTRACT FROM AUTHOR]

The (plagioclase) lherzolitic shergottite Northwest Africa (NWA) 7397 consists of poikilitic and non‐poikilitic lithologies. Coarse‐grained low‐Ca pyroxene oikocrysts enclose olivine and chromite grains in the poikilitic lithology. The major constituents of the non‐poikilitic lithology are olivine, Ca‐pyroxene, and plagioclase. Minor amounts of chromite, ilmenite, alkali feldspar, Ca‐phosphate, and iron‐sulfide are included in the non‐poikilitic lithology. Most plagioclase grains in the non‐poikilitic lithology have become maskelynite. A melt pocket occurs in the non‐poikilitic lithology. Plagioclase in contact with the melt pocket has dissociated into zagamiite + stishovite. Apatite and merrillite entrained in the melt pocket have transformed into tuite. Olivine in contact with the melt pocket has dissociated into bridgmanite (almost vitrified) + ferroan‐periclase. Alteration products, iron oxides and hydroxides, also occur in the dissociated olivine although it is not clear when the aqueous alteration occurred. The dissociation reactions of olivine and plagioclase into the high‐pressure polymorphs (bridgmanite, ferroan‐periclase, zagamiite, and stishovite) are found from lherzolitic shergottites for the first time. The estimated peak shock‐pressure and ‐temperature conditions recorded in melt pockets of NWA 7397 are ˜23 GPa and 2,000 °C at least, respectively, based on the high‐pressure mineral assemblages. [ABSTRACT FROM AUTHOR]

We have conducted petrological and mineralogical studies on an igneous clast in the Northwest Africa (NWA) 1685 (LL4) chondrite. This meteorite was described in the Meteoritical Bulletin as containing clasts similar to alkali‐rich clasts in LL chondritic breccias Yamato (Y)‐74442 (LL4), Bhola (LL3‐6), and Krähenberg (LL5). We carefully compared the textures, as well as mineral and matrix compositions, of the NWA 1685 clast with those of the previously described alkali‐rich clasts in the LL chondritic breccias. Olivine grains are embedded in glassy matrix and have no chemical zoning. Shock melt veins and fractures were observed only in olivine grains and did not continue into matrix. Potassium abundance of matrix glasses of the NWA 1685 clast is lower than those of alkali‐rich igneous clasts in Y‐74442, Bhola, and Krähenberg, indicating that the igneous clasts in NWA 1685 are different from the alkali‐rich clasts previously reported in the LL chondritic breccias. The NWA 1685 clast might have formed during an impact melting and quenching event on the LL‐chondrite parent body, and then been incorporated into a breccia. [ABSTRACT FROM AUTHOR]

We report bulk composition data for 235 stones of ~77 lunar meteorites from northern Africa and 33 lunar meteorites from elsewhere. About 27% of the African meteorites are typical feldspathic lunar rocks, all breccias of similar bulk composition, for example, 3–5% FeO and low concentrations of incompatible elements. Nevertheless, these meteorites have a large range in Mg' (whole‐rock mole% Mg/[Mg + Fe]), 57–77 (mean: 65.5), and this parameter does not correlate with either albite content of the plagioclase or concentrations of incompatible elements. From this observation, we conclude that feldspathic lunar meteorites do not support the hypotheses that the anorthositic, precursor plutonic rocks of the meteorite breccias all crystallized from a common magma. Among feldspathic lunar meteorites, Mg' increases with normative olivine abundance but is uncorrelated with normative pyroxene abundance, that is, high‐Mg' feldspathic rocks of the early lunar crust were troctolitic, not noritic. The NWA 5744 (Northwest Arica) clan of lunar meteorites are anorthositic troctolites (59–75% plagioclase, 15–26% olivine, Fo77–80) with very low concentrations of incompatible elements (2.6 × CI) compared to troctolites in the Apollo collection. They may represent the lower feldspathic crust or differentiated impact melt from portions of the highlands distant from the PKT (Procellarum KREEP Terrane). About 31% of the lunar meteorites from northern Africa, all breccias, are, by lunar standards, moderately mafic (5–13% FeO) but more magnesian than mixtures of typical feldspathic meteorite and mare basalt, implying that they represent moderately mafic regions of the highlands or originate from the South Pole–Aitken basin. With ~6 µg g−1 Th, two NWA meteorites likely originate from the PKT. Including the unique NWA 773 clan, at least six of the northern Africa meteorites are, or are dominated by, unbrecciated basalts and gabbros of mare affinity. We estimate that the ~341 lunar meteorite stones (Africa and elsewhere) for which there are data represent 131–147 terrestrially unpaired meteorites and 109–134 lunar launch sites. [ABSTRACT FROM AUTHOR]

The similarities between CV and CK chondrites are so substantial that some studies have argued for a common parent body origin. These similarities also mean that they are susceptible to misclassification as one another. It is, therefore, important to accurately classify CV and CK chondrites to properly compare the properties of the two groups and evaluate the single parent body hypothesis. In this study, we re‐evaluate the current classification of Northwest Africa (NWA) 2900 as a CV3 chondrite. Based on chondrule abundance (~13%), average chondrule diameter (1.11 ± 0.67 mm), iron content in chondrule olivine (Fa1 to Fa35 with a peak near ~Fa31) and matrix olivine (Fa33 to Fa36), magnetite abundance (~4 vol%), elemental abundances in olivine (Cr2O3, Al2O3, TiO2, MnO, NiO, and CaO) and magnetite (Cr2O3, Al2O3, TiO2, and NiO), and comparison with previously reported data for CV and CK chondrites, we propose that the classification of NWA 2900 be changed from CV3 chondrite to CK3 chondrite, with characteristics most similar to those of the CK3.8 subtype. We additionally suggest minor modifications to the compositional criteria used to distinguish between CV and CK chondrites and demonstrate that NWA 2900 extends the range of bulk oxygen isotope compositions of CK chondrites. [ABSTRACT FROM AUTHOR]

Northwest Africa (NWA) 032 is an unbrecciated porphyritic basalt found in the Moroccan desert in 1999. Constituent igneous minerals—olivine, pyroxene, and plagioclase—exhibit shock deformation and transformation effects. NWA 032 is among the youngest radiometrically dated sample from the Moon, with concordant Sm‐Nd and Rb‐Sr ages of 2.947 ± 0.016 Ga and 2.931 ± 0.092, respectively, representing the timing of igneous crystallization. We present the first comprehensive study of shock metamorphism in NWA 032, with a focus on the structural state of fine‐grained plagioclase feldspar, shock deformation in olivine and pyroxene, and the microtexture and mineralogy of shock melts. Micro‐Raman spectroscopy, optical properties, and electron imaging confirm that plagioclase in this meteorite has been shock amorphized, which, for calcic plagioclase (An80‐90), requires shock pressures on the order of ~25–27 GPa. Shock pressures in this range are accompanied by a postshock temperature increase <200 °C. Shock deformation in olivine and pyroxene phenocrysts comprises undulose extinction to weak mosaicism, irregular fractures, polysynthetic mechanical twinning in pyroxene, and development of planar fractures in olivine. The shock effects in mafic minerals constrain the upper limit of shock in NWA 032 to have been <30 GPa. Shock melt in NWA 032 has quenched to glass of basaltic composition, representing localized in situ melting of igneous minerals by shearing along lithological boundaries to form shock veins and shock impedance contrasts to form isolated pockets of shock melt. These melts quench‐crystallized olivine and pyroxene during the pressure release (<14 GPa). Using recent experimental data on shock amorphization of feldspars, coupled with constraints on the formation of metastable minerals associated with shock melt, we have revised the shock pressure experienced by paired meteorites NWA 10597, NWA 4734, and LaPaz Icefield 02205/02224/0226/02436/03632/04841. These largely unbrecciated, basaltic meteorites experienced an equilibration shock pressure on the order of ~22–25 GPa, constrained by partial amorphization of precursor igneous bytownite. Our results are consistent with crater pairing and ejection in a single impact cratering event. [ABSTRACT FROM AUTHOR]

Carbonatites are unusual, carbon-rich magmas thought to form either by the melting of a carbon-rich mantle source or by low-degree partial melting of a carbon-poor (<80 ppm C) mantle followed by protracted differentiation and/or immiscibility. Carbonate-bearing mantle xenoliths from Oldoinyo Lengai (East African Rift), the only active volcano erupting carbonatites, have provided key support for a C-rich mantle source. Here, we report unique microscale O and C isotopic analyses of those carbonates, which are present as interstitial grains in the silicate host lava, veins in the xenoliths, and pseudo-inclusions in olivine xenoliths. The δ18O values vary little, from 19‰ to 29‰, whereas δ13C values are more variable, ranging from -23‰ to +0.5‰. We show that such carbonate δ18O values result from the low-temperature precipitation of carbonate in equilibrium with meteoric water, rather than under mantle conditions. In this framework, the observed δ13C values can be reproduced by Rayleigh distillation driven by carbonate precipitation and associated degassing. Together with petrological evidence of a physical connection between the three types of carbonates, our isotopic data support the pedogenic formation of carbonates in the studied xenoliths by soil-water percolation and protracted crystallization along xenolith cracks. Our results refute a mechanism of C enrichment in the form of mantle carbonates in the mantle beneath the Natron Lake magmatic province and instead support carbonatite formation by low-degree partial melting of a C-poor mantle and subsequent protracted differentiation of alkaline magmas. [ABSTRACT FROM AUTHOR]

Diogenites are a group of meteorites that are derived from the interior of the largest protoplanet Vesta. They provide a unique opportunity to understanding together the internal structure and dynamic evolution of this protoplanet. Northwest Africa (NWA) 8321 was suggested to be an unbrecciated noritic diogenite meteorite, which is confirmed by our oxygen and chromium isotopic data. Here, we find that olivine in this sample has been partly replaced by orthopyroxene, troilite, and minor metal. The replacement texture of olivine is unambiguous evidence of sulfur-involved metasomatism in the interior of Vesta. The presence of such replacement texture suggests that in NWA 8321, the olivine should be of xenolith origin while the noritic diogenite was derived from partial melting of pre-existing rocks and had crystallized in the interior of Vesta. The post-Rheasilvia craters in the north-polar region on Vesta could be the potential source for NWA 8321. The authors here analyse the petrology of the meteorite NWA 8321 (parent body Vesta). They find sulfidation processes of olivine suggesting metasomatism in the Vestan interior and a partial melting origin for the host noritic diogenite. [ABSTRACT FROM AUTHOR]

Northwest Africa (NWA) 869 is the largest sample of chondritic regolith breccia, making it an ideal source for research on accretionary processes and primordial chemical mixing. One such process can be seen in detail through the first identification of a eucrite impactor clast in an L chondrite breccia. The ~7 mm diameter clast has oxygen isotope compositions (Δ17O = −0.240, −0.258‰) and pigeonite and augite compositions typical for eucrites, but with high areal abundance of silica (9.5%) and ilmenite (1.5%). The rim around the clast is a mixture of breccia and igneous phases, the latter due to either impactor‐triggered melting or later metamorphism. The rim has an oxygen isotope composition falling on a mixing line between known eucrite and L chondrite compositions (Δ17O = 0.326‰) and, coincidentally, on the Mars fractionation line. Pyroxene grains from the melt component in the rim have compositions that fall on a mixing line between the average eucrite pyroxene composition and equilibrated L chondrite composition. The margins of chondritic olivine crystal clasts in the rim are enriched in Fe as a result of diffusion from the Fe‐rich melt and suggest cooling on the scale of hours. The textures and chemical mixing observed provide evidence for an unconsolidated L chondrite target material, differing from the current state of NWA 869 material. The heterogeneity of oxygen isotope and chemical signatures at this small length scale serve as a cautionary note when extrapolating from small volumes of materials to deduce planetesimal source characteristics. [ABSTRACT FROM AUTHOR]

Kimberlites are the deepest melts produced on Earth that are erupted at the surface and can therefore provide unique insights into the composition and evolution of the mantle. Radiogenic isotopes provide ambiguous evidence for the occurrence of recycled crustal material in kimberlite sources. Oxygen isotopes can fractionate significantly only in the shallow crust, and thus represent a powerful tracer of subducted material in the sources of kimberlite. To constrain the oxygen isotope composition of kimberlite melts, we have examined olivine grains in eleven Cretaceous to Eocene archetypal kimberlites from southern Africa, Lac de Gras (Canada) and Alto Paranaiba (Brazil), which exhibit radiogenic isotope evidence for recycled crustal material in their sources including highly radiogenic Pb isotopes and Nd-Hf isotope compositions deviating below the mantle array. Olivine grains are commonly zoned between a mantle-derived xenocrystic core and one or more magmatic overgrowths, i.e. occasional internal zones, ubiquitous rims and rare rinds (moving outward from the core). The oxygen isotope composition of different olivine zones was determined in situ within separated olivine grains by secondary ion mass spectrometry (SIMS) after point selection using back-scattered electron (BSE) images combined with major and minor element analyses. With the exception of a few cores, the δ18O values of different olivine zones do not deviate from typical mantle olivine values of 5.18 ± 0.28‰ (Mattey et al., 1994). There are no correlations between oxygen isotopes and major/minor element compositions for internal zones and rims from individual localities or in the entire dataset. This indicates that the oxygen isotope composition of kimberlite melts is not affected by melt differentiation to the point of olivine rim crystallisation. However, olivine rinds from the Koala kimberlite (Canada) display an inverse correlation between δ18O and Mn-Ca concentrations, with δ18O values extending below the mantle range, which is probably due to carbonate fractionation, CO 2 degassing and/or assimilation of serpentine-rich material after kimberlite emplacement in the upper crust. The mantle-like δ18O composition of olivine internal zones and rims suggests that assimilation of mantle material and liberation of a CO 2 -rich phase during ascent in the mantle do not significantly modify the original δ18O signature of kimberlite melts. Modelling of oxygen isotope fractionation shows that up to 15 wt% of CO 2 can be lost by kimberlites en route to the upper crust. Our results combined with mass balance calculations indicate that only a limited amount (<5–10 wt%) of recycled crustal material could occur in the source of kimberlites from southern Africa, Lac de Gras and Alto Paranaiba, or that the recycled material had an oxygen isotope composition similar to the mantle. [ABSTRACT FROM AUTHOR]

Northwest Africa (NWA) 10414 is an unusual shergottite with a cumulate texture. It contains 73% coarse prismatic pigeonite, plus 18% interstitial maskelynite, 2% Si‐rich mesostasis, 2% merrillite, and minor chromite‐ulvöspinel. It contains no olivine, and only ~3% augite. Phase compositions are pigeonite (En68‐43Fs27‐48Wo5‐15) and maskelynite An~54‐36, more sodic than most maskelynite in shergottites. Chromite‐ulvöspinel composition plots between the earliest and most fractionated spinel‐group minerals in olivine‐phyric shergottites. NWA 10414 mineralogically resembles the contact facies between Elephant Moraine 79001 lithologic units A and B, with abundant pigeonite phenocrysts, though it is coarser grained. Its most Mg‐rich pigeonite also has a similar composition to the earliest crystallized pyroxenes in several other shergottites, including Shergotty. The Shergotty intercumulus liquid composition crystallizes pigeonite with a similar composition range to NWA 10414 pigeonite, using PETROLOG. Olivine‐phyric shergottite NWA 6234, with a pure magma composition, produces an even better match to this pigeonite composition range, after olivine crystallization. These observations suggest that after the accumulation of olivine from an olivine‐phyric shergottite magma, the daughter liquid could precipitate pigeonite locally to form this pigeonite cumulate, before the crystallization of overlying liquid as a normal basaltic shergottite. [ABSTRACT FROM AUTHOR]

In part 1 of our examination of Martian meteorite Northwest Africa 8159 (NWA 8159) we illustrated many interesting mineralogical and textural attributes that make this martian basalt unique. Unlike the shergottites that illustrate a clear relationship between the extent of trace element and isotopic characteristics and oxygen fugacity (reduced, depleted magmas; oxidized, enriched magmas), NWA 8159 illustrates a decoupling of this relationship as it has oxidized and depleted signatures. In part 2, using a series of new observations and measurements (Cl isotopes, XANES, TEM, empirical modeling) we use NWA 8159 to explore the interaction between mantle-derived magmas and the martian crust. The magnetite-orthopyroxene intergrowths associated with olivine are a product of a martian subsolidus oxidation event near the QFM buffer and not a magmatic reaction in an oxidizing magma (>QFM + 3). This subsolidus event is further supported by Cr valence in the olivine, alteration of P-rich olivine, and end-member magnetite in the matrix of the meteorite. Although this subsolidus alteration makes it extremely difficult to determine the original f O 2 of the parental magma for NWA 8159, there is evidence that during the initial stages of crystallization the f O 2 was modestly reducing (∼IW + 1). Potential manifestations of more reducing magmatic conditions include P-rich cores in the olivine and low Fe3+ in silicates (plagioclase, pyroxene). Further, if analogous to all other depleted shergottites, NWA 8159 initially crystallized under reducing conditions. This decoupling between oxygen fugacity and isotopic-trace element characteristics suggests that basalts derived from the martian mantle interacted with the crust in ways that significantly influenced redox history and volatile element isotopic composition (Cl, S), without dramatically modifying many of its radiogenic isotope and trace element mantle fingerprints. [ABSTRACT FROM AUTHOR]

Introduction: Lunar meteorite Northwest Africa (NWA) 14340 was found in Algeria in 2017 as a single 8.26 gram stone that has been classified as a clast-rich, matrix-supported feldspathic breccia. A partially glassy spherule indicates that this meteorite was part of the lunar regolith. Recently, high-pressure minerals have been documented from the matrix of ten lunar meteorite breccias, which constrain the temperature-pressure conditions of the shocklithification process [1, 2]. In this study, we characterize the mineralogy and petrology of NWA 14340, with a focus on shock effects in lithic clasts, and the nature of the matrix between these macroscopic components, using electron microscopy and Raman spectroscopy. These results help to unravel the impact history of lunar regolith components and how they evolve to become coherent rocks. Results: NWA 14340 contains various types of lithic clasts including norite, olivine-gabbro, basalt, and devitrified glass, listed in descending order of abundance, and mineral fragments, that are set in a fine-grained to glassy matrix. The major minerals are plagioclase (An92.0-An98.1), olivine (Fa17.4-Fa35.4, FeO/MnO = 88.2 ± 5, N = 21), and pyroxene (En13.0-36.7Wo2.5-41.2, FeO/MnO = 52.3 ± 4, N = 26). Some pyroxene contains augite exsolution lamellae (En15.6-16.2Wo40.3-40.9, FeO/MnO = 46.5 ± 4, N = 8). Minor phases include silica, ilmenite, troilite, and FeNi metal and accessory zircon. Lithic fragments are highly shocked. Pyroxene exhibits mechanical twinning, mosaicism and planar fractures. The majority of plagioclase in lithic clasts is amorphous, found either as diaplectic glass or glass containing flow lines and vesicles. The most highly shocked clasts exhibit pyroxene / plagioclase grain boundary melting. Olivine exhibits planar fractures and mosaicism. The matrix interstitial to these clasts comprises flow-textured, vesiculated glass. Small, rounded blebs of troilite in surrounding glass are consistent with partial melting. Within the glass, 1-10 µm size crystals are heterogeneously distributed. The occurrence, grain size and grain shape of these crystals are similar to that reported by [1, 2] for other lunar regolith breccias. Some of these crystals are identified as tissintite II [3]-a high-pressure, vacancy-rich pyroxene-structured mineral enriched in Mg, Fe and Cr-compared with tissintite, which has a plagioclase composition (An58-69) [4]. Other, as yet unidentified, silicate minerals have crystallized from the melt, which will be constrained using Raman spectroscopy. Discussion: The structural state and composition of feldspar, coupled with deformation in olivine and pyroxene, constrain the conditions of shock metamorphism [5]. The shock pressures experienced by clasts in NWA 14340 range from ~25-27 GPa and <30 GPa to >45 GPa. Experimentally-formed tissintite is stable at pressures of 4.5-10 GPa and a temperature of >1273 K [6]. Other minerals, in addition to tissintite-II, that have crystallized in the NWA 14340 matrix will need to be identified in order to unravel the history of the shock-lithification process recorded in this meteorite. [ABSTRACT FROM AUTHOR]

Introduction: Northwest Africa 14713 is a new poikilitic Martian meteorite discovered in 2021 with a total mass of ~3 kg. Martian meteorites are currently the only samples of Mars available for direct study by Earth-based laboratories. The shergottites are the youngest of the Martian meteorites predominantly having formed during the late Amazonian period with crystallization ages ranging from 165 to 225 Ma [1]. They represent ~82% by mass of the known Martian meteorites and can be divided further into four distinct sub-groups: pyroxene-phyric (basaltic), olivinephyric, gabbroic and poikilitic [2]. There are currently only ~276 examples of shergottites, and of those only ~12% display a poikilitic texture (Meteoritical Bulletin Database). With such a limited number of examples available it is important that we continue to expand this sampling through the continued analysis and classification of newly discovered Martian meteorites to better understand the petrogenic relationship that exists between the shergottite subgroups and Martian meteorites in general. Diagram 1. Pyroxene ternary plot for NWA 14713; Image 1. Photograph of hand sample of NWA 14713; Image 2. BSE image of NWA 14713 converted to binary using ImageJ showing maskelynite in black. Image 3. 200x reflected light image of poikiloblastic texture with olivine chadacrysts embedded in pyroxene oikocrysts. Petrography: NWA 14713 was studied using a polished microprobe mount. Examination of the mount with electron microprobe and image analysis using ImageJ shows it contains numerous poikiloblastic olivine chadacrysts embedded within pigeonite and augite oikocrysts. Modal analysis shows ~25% igneous-zoned olivine, ~35% igneouszoned pyroxene and ~35% maskelynite. Augite is subcalcic with pyroxene phases dominated by relatively low-Ca pigeonite. No lo-Ca pyroxenes were detected. Three types of Cr-spinels were detected and analyzed: high-Cr Ti-spinel with Ti8.81, Cr17.35, high-Ti Cr-spinel with Ti4.58, Cr27.49, and low-Ti Cr-spinel with Cr38.74, Ti0.63 (all Wt%). Other minor phases observed were ilmenite, merrillite, and troilite. Geochemistry: Olivine Fa35.4±2.8 n=10; pigeonite Fs25.7±3.2Wo9.2±2.4, n=8; augite Fs16.5±1.0Wo34.6±1.3, Fe/Mn=26±3, n=3; plagioclase An54.8±1.2Ab43.9±1.2, Or 1.3±0.2, n=5. Discussion: Microprobe analysis indicates this meteorite is a Martian poikilitic shergottite. It is a Martian based on Fe/Mn ratios of both olivine and pyroxenes. It is a poikilitic shergottite based on pyroxene plots, modal abundances, and poikiloblastic embedding of olivine chadacrysts within pyroxene oikocrysts [3]. [ABSTRACT FROM AUTHOR]

Introduction: Shergottites record recent igneous activity of Mars and analyzing these samples allow us to understand magmatic compositions and their crystallization processes [e.g., 1-3]. However, the size of Martian meteorites that can be analyzed in the laboratory is limited, and mineralogical information is usually from a few cm scale of polished fs. Therefore, if we can analyze larger samples, we can better understand the diversity of the petrological texture and mineral compositions. In this study, we tried to directly analyze a NWA 13366 slab whose size is ~5 cm across by electron microprobe (EPMA) to determine textural and compositional differences on such a scale. Sample and Methods: We analyzed a polished slab of NWA 13366 (~5 x 5 cm). Elemental maps were obtained using a JEOL JXA-8900L EPMA at Univ. of Tokyo (15 kV acceleration voltage and 80 nA beam current). The elemental maps were then used for quantitative analysis of olivine and pyroxene in both poikilitic and non-poikilitic lithologies. The quantitative analysis was set up at acceleration voltage of 15 kV and beam current of 12 nA. Results: Fig. 1 shows a Ca map of the NWA 13366 slab analyed. It is obvious that NWA 13366 is a poikilitic shergottite containg scattered pyroxene oikocrysts (~5 mm) enclosing olivine chadacrysts. Most of the sample is showing a non-poikilitic texture and the poikilitic lithology is only 10-20 vol.% (region I). However, it is noted that at the upper part of the slab there is an area where pyroxene oikocrysts dominate (Fig. 1). Fig. 1 further shows that pyroxene oikocrysts have Ca-rich rims (augite) in both regions, but the core in region II is more Ca-poor than that in region I (Fig. 2). The rim of the pyroxene oikocryst in region II is thinner than that of region I and has a smaller chemical compositional range than region I. The Mg#s of olivine chadacrysts and pyroxene oikocrysts are also slightly different between regions I and II. In region I, the range of Mg# in olivine chadacrysts is 0.74-0.65 and the highest Mg# of pyroxene oikocrysts is 0.80. On the other hand, in region II, the range of Mg# in olivine chadacrysts is 0.76-0.61 and the highest Mg# of pyroxene oikocrysts is 0.81. There is no clear variation for the Mg# of olivine and pyroxene in non-poikilitic lithologies of both regions. Discussion and Conclusion: The textural and compositional differences of two regions found in the 5 cm slab of NWA 13366 suggest that Mg-rich olivine first crystallized in the magma reservoir at depth and pyroxene subsequently crystallized enclosing olivine. Some early formed crumps of such oikocrysts were accumulated to form region II. The later formed oikocrysts were similarly accumulated, but the abundance was low and mostly crystallized when oikocryst-bearing magma moved near the surface to crystallize non-poikilitic lithology forming region I. Thus, this study suggests that a wide petrological variation of poikilitic shergottite may result from a few cm scale heterogeneity of the sample [e.g., 1]. [ABSTRACT FROM AUTHOR]

Introduction: It has been inferred from experimental modelling that lunar dunites, olivine-rich rocks, crystallized as early stage cumulates from the lunar magma ocean (LMO) and make up a significant fraction of the lunar mantle [1-2]. Although basin-forming impact events on the lunar surface could have exposed lunar mantle rocks [3-4], dunite clasts are rarely observed in both Apollo [4-6] and lunar meteorite samples [7-9]. Most dunite clasts previously examined are suggested to originate either as cumulates of basaltic magmas from a shallow crustal source [4-5], or more commonly, as cumulates of Mg-suite magmas from a deep crustal source [8-9]. As it would be of great importance to identify lunar dunite clasts that are unequivocally mantle-derived [10], we investigated the petrology of a dunite clast from lunar fragmental breccia Northwest Africa (NWA) 14900 in order to constrain either a crustal or mantle source. Petrography: The 2.2 mm dunite clast is sub-angular in appearance and is crosscut by an interconnected network of cracks and veins containing terrestrial carbonate weathering products. The dunite clast is almost entirely monomineralic, consisting of ~99.2 vol. % olivine and ~0.8 vol. % chromite. It exhibits a fine-grained, granular texture (120° triple junctions are moderately observed along olivine grain boundaries) composed of interlocking, fractured olivine grains (Av. grain size ~110 μm, up to ~290 μm) enclosing sub-rounded, elongate grains of chromite (Av. grain size ~20 μm, up to ~50 μm). Geochemistry: Olivine grains in the dunite clast appear unzoned in both major and minor elements, and are compositionally uniform (Fa9.1±0.1, range Fa9.0-9.1, Mg#=91, CaO and Cr2O3 wt. % = <0.1, FeO/MnO=80±10, n=8); chromite grains appear unzoned and are compositionally uniform (Cr#=79.3±0.3, Mg#=51.3±1.0, n=2). Olivine-Spinel Geothermometry: The equilibration temperature of the dunite clast was calculated using the average Cr# of chromite grains, the average Sp-Ol KDFe-Mg of the dunite clast, and the olivine-spinel geothermometer equation derived from [11]; this resulted in an equilibration temperature for the dunite clast of 967±11°C. However, this temperature represents a lower limit estimate of the initial magmatic crystallization temperature for the dunite clast, since the deviation of Sp-Ol KDFe-Mg from the Ol-Sp equilibrium line of [9] indicates that sub-solidus re-equilibration of the dunite clast had taken place following crystallization. Discussion: Compared with other lunar dunite clasts, the texture, grain size, and unzoned, equilibrated nature of olivine grains in the dunite clast from NWA 14900, and its calculated equilibration temperature, are most similar to that of a hypothesized mantle-derived lunar dunite clast reported in NWA 11421 [7]. However, the absence of plagioclase and pyroxene in this dunite clast combined with it having a higher olivine Mg# indicates that this dunite clast crystallized at a higher temperature than the dunite clast in [7], likely at a greater depth. Olivine compositions from the dunite clast are most similar to those reported in lunar Mg-suite dunites (Mg#~85-90) [8-9], but the chromite Cr# of the dunite clast is noticeably higher when compared to lunar Mg-suite dunites (Cr#~61-72) [8-9], indicating crystallization of this dunite clast from either a more primitive Mg-suite parent magma, or a non-Mg-suite-related magma. In summary, the dunite clast in NWA 14900 is texturally and chemically distinct from other dunite clasts reported in both Apollo and lunar meteorite samples, and likely represents either 1) a fragment derived from the lunar mantle (an early LMO cumulate or an Mg-suite partial melt residue), or 2) the most primitive Mg-suite dunite sampled thus far. [ABSTRACT FROM AUTHOR]

Introduction: Nakhlites make up ~8% of the total number of martian meteorites and are cumulate clinopyroxenerich rocks from Mars linked by shared crystallization ages (1340 ± 40 Ma) and cosmic ray exposure ages (11 ± 1.5 Ma) [1-2]. These shared properties make the 26 known nakhlites the largest suite of igneous rocks from a common provenance on any planetary body besides the Moon and Earth. As such, nakhlites are important for understanding relatively recent magmatic and volcanic processes on Mars. Northwest Africa (NWA) 13669 is a recently-found nakhlite. Here we present major, minor, and trace element bulk rock and mineral analyses in addition to quantitative textural analyses to assess the formation and emplacement of NWA 13669 and its relation to other nakhlites. Methods: Bulk rock major and trace elements were conducted at Scripps Institution of Oceanography using an ICP-MS following the sample preparation and analytical methodology described in [3]. Mineral major element analyses were performed in situ using a JEOL JXA-8900 electron probe microanalyzer housed at the University of Nevada, Las Vegas (UNLV) following the method described in [2]. Mineral trace element analyses were conducted in situ using an NWR 139 laser ablation system coupled to an ICP-MS at UNLV. The laser was operated at 15 Hz and a fluence of ~3 J/s was maintained with an ablation time of 40 s and 10 s washout times. Spot size ranged from 50-100 μm depending on the size of the mineral of interest. Standardization was done using NIST 610 glass and BHVO-2, and data was reduced using iolite4 [4]. Crystal size distributions (CSD) were performed following the technique outlined in [5]. Results: Northwest Africa 13669 displays a cumulate texture of elongate euhedral to subhedral augite and cumulus olivine with intercumulus plagioclase and glass. Minor phases include Fe-Ti oxides, apatite, and pyrrhotite. Average modal abundances between both sections analyzed in this study are 63% augite, 16% olivine, 10% plagioclase, 8% glass, and 3% Fe-Ti oxide. Crystal size distribution profiles for both sections of NWA 13669 display a negative concave-up sublinear shape and are broadly similar to other nakhlite CSD [2, 6, 7]. The bulk rock Mg# of NWA 13669 is 38.1, lower than most reported nakhlites (Mg# = 35.6-50.8) [2, 6, 8]. Calcium in NWA 13669 is among the lowest (11 wt.%) reported for nakhlites, and FeO (25.6 wt.%) and MnO (0.65 wt.%) are the highest. The CI-chondrite normalized rare earth element (REE) pattern for NWA 13669 has a light REE (LREE) enrichment with a (La/Lu)CI of 3.7 and depletion in the heavy REE (HREE), characteristics shared by the nakhlites. Pyroxene in NWA 13669 is augite and normally-zoned from Mg and Ca-rich cores (En36Fs25Wo39) to Ferich rims (En31Fs32Wo37). Rare earth element (REE) profiles in NWA 13669 augite cores are relatively flat with a slight negative Eu anomaly (Eu/Eu* = 0.75). Olivine compositions are homogeneous (Fo28.8) with only minor intragrain variations from core to rim. Plagioclase in NWA 13669 is albite-rich (An37Ab60Or3) with limited major-element variations, and intercumulus glass is alkali- and REE-rich with microlitic inclusions (> 1μm) of pyroxene, Fe-Ti oxides, and apatite. Apatite is F-rich (> 3 wt.%) and the dominate REE carrier. Discussion: Pyroxene modal abundance in NWA 13669 is similar to NWA 817 (63%) and NWA 10645 (62%), though the occurrence of both plagioclase and glass in the intercumulus material is most similar to Caleta el Cobre (CeC) 022. The augite CSD profiles for NWA 13669 are also similar to NWA 10645 and the Yamato pairing group, suggesting similar emplacement conditions and supports the findings of [2] that nakhlites originate from multiple flows, dikes, or sills on Mars. The bulk rock and mineral REE patterns in NWA 13669 are similar to those observed for other nakhlites, indicating NWA 13669 crystallized from a parental melt derived from the same geochemically depleted source reservoir, then underwent subsequent modification by Cl and LREE-rich fluids [9]. Major element augite compositions display a Ca-depletion from core to rim, consistent with a single batch of melt. Overlap between pyroxene core and rim analyses in tandem with unzoned olivine, which has also been reported in NWA 998, Lafayette, and CeC 022, could be evidence for reequilibration and long-term magma storage for nakhlites [10]. Overall similarities in texture, modal abundances, and CSDs suggest NWA 13669 was emplaced under similar conditions to NWA 10645. However, the distinct bulk rock and mineral chemistry from previously reported nakhlites could indicate NWA 13669 is a previously unsampled flow, dike, or sill. Continued work using melt inclusion analyses is underway to further establish the relationship between NWA 13669 and previously studied nakhlites and to potentially determine the parental melt composition. [ABSTRACT FROM AUTHOR]

A thermobarometric and petrologic study of basanites erupted from young volcanic cones along the submarine portions of the three El Hierro rift zones (NE-Rift, NW-Rift and S-Ridge) has been performed to reconstruct magma plumbing and storage beneath the island. Mineral-melt thermobarometry applied to naturally quenched glass and clinopyroxene rims yields pressures ranging from 350 to 1070 MPa with about 80% of the calculated pressures being in the range of 600–800 MPa. This corresponds to a depth range of 19–26 km, implying that the main level of final crystal fractionation is within the uppermost mantle. No systematic dependence between sample locality and fractionation pressures could be observed. Olivine and clinopyroxene crystals in the rocks are complexly zoned and have, on an inter-sample as well as on an intra-sample scale, highly variable core and rim compositions. This can best be explained by mixing of multiply saturated (olivine, magnetite, clinopyroxene, ilmenite), moderately evolved magmas with more mafic magmas being either only saturated with olivine + spinel or with olivine + spinel + clinopyroxene. The inter-sample differences indicate derivation from small, isolated magma chambers which have undergone distinct fractionation and mixing histories. This is in contrast to oceanic intraplate volcanoes situated on plumes with high melt supply rates, e.g. Kilauea Volcano (Hawaii), where magma is mainly transported through a central conduit system and stored in a shallow magma chamber prior to injection into the rift zones. The plumbing system beneath El Hierro rather resembles the magma storage systems beneath, e.g. Madeira or La Palma, indicating that small, intermittent magma chambers might be a common feature of oceanic islands fed by plumes with relatively low fluxes, which results in only limited and periodic magma supply. [ABSTRACT FROM AUTHOR]

Due to their common occurrence in various types of chondrites, igneous rims formed on pre-existing chondrules throughout chondrule-forming regions of the solar nebula. Although the peak temperatures are thought to reach similar values to those achieved during chondrule formation events, the heating duration in chondrule rim formation has not been well defined. We determined the two-dimensional chemical and oxygen isotopic distributions in an igneous rim of a chondrule within the Northwest Africa 3118 CV3 oxA chondrite with sub-micrometer resolution using secondary ion mass spectrometry and scanning electron microscopy. The igneous rim experienced aqueous alteration on the CV parent body. The aqueous alteration resulted in precipitation of the secondary FeO-rich olivine (Fa 40–49) and slightly disturbed the Fe-Mg distribution in the MgO-rich olivine phenocrysts (Fa 11–22) at about a 1 μm scale. However, no oxygen isotopic disturbances were observed at a scale greater than 100 nm. The MgO-rich olivine, a primary phase of igneous rim formation, has δ17O = −6 ± 3‰ and δ18O = −1 ± 4‰, and some grains contain extreme 16O-rich areas (δ17O, δ18O = ∼−30‰) nearly 10 μm across. We detected oxygen isotopic migration of approximately 1 μm at the boundaries of the extreme 16O-rich areas. Using oxygen self-diffusivity in olivine, the heating time of the igneous rim formation could have continued from several hours to several days at near liquidus temperatures (∼2000 K) in the solar nebula suggesting that the rim formed by a similar flash heating event that formed the chondrules. [ABSTRACT FROM AUTHOR]