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The Cavezzo meteorite, which fell on January 1, 2020, is the first meteorite detected and recovered by the Italian PRISMA Fireball Network. Two specimens, weighing 3.12 g (specimen 1) and 52.19 g (specimen 2), were collected 3 days after the bolide was observed, thanks to an effective media campaign that encouraged the involvement of local people. The two specimens of this meteorite have not only completely different lithological characteristics but also a different geochemistry and oxygen isotopic composition as well. Specimen 1 is anomalous both for the textural–structural features, varying seamlessly from chondritic to “achondritic,” and a very unusual modal mineralogy—such as the relatively high amount of olivine (63.1 vol%), plagioclase (18.2 vol%), high-Ca pyroxene (10.3 vol%), and chlorapatite (2.1 vol%); and the unusually low content of low-Ca pyroxene (5.8 vol%), metal (0.1 vol%), and troilite (much lesser than 0.1 vol%)—although the compositional values for olivine (Fa 24.24 mol%) and low-Ca pyroxene (Fs 20.41 mol%) appear to be similar to those of the L chondrite group. Conversely, in specimen 2, not only the texture and the crystal chemistry but also the modal mineralogy (low-Ca pyroxene much more abundant than high-Ca pyroxene and occurrence of metal and sulfides) look like those of an ordinary L chondrite. The differences between the two specimens are also confirmed by geochemistry. The oxygen isotope composition of specimen 1 plots at the boundary between the H and L groups (δ17O‰ 3.250; δ18O‰ 4.736; Δ17O‰ 0.788) whereas specimen 2 plots at the boundary of the L and LL fields (δ17O‰ 3.737; δ18O‰ 4.957; Δ17O‰ 1.159). The bulk chemistry shows a different content of many minor and trace elements (including rare earth elements), such as a strong depletion of siderophile and chalcophile elements in specimen 1. The two specimens then do not contain fragments of each other, thus preventing us from classifying this “double face” meteorite as an ordinary chondrite breccia. In detail, specimen 1 can be considered a “xenolith” in which chondritic structure and igneous texture coexist without discontinuity, and therefore, it represents a previously unsampled portion of the L parent body. In summary, these findings support the classification of Cavezzo as an L5 anomalous chondrite.

International audience; Olivine-hosted melt inclusions (MIs) from tephra of the recent 2013–2018 activity at Mt. Etna were investigated for assessing the chemical evolution of magmas and quantifying their pre-eruptive volatile budget. Microanalyses revealed two types of MIs present in all investigated eruptions; the inclusions, particularly the less evolved ones, appear to have experienced water loss coupled with SiO2 depletion. Restoration ofthe original SiO2-H2O concentrations provides consistency with the thermodynamic modelling of magma evolution. The two types of MIs developed during crystallization of olivine plus clinopyroxene between 200 and 100 MPa, where magmas also experienced CO2 flushing. Degassing processes at these levels are responsible for water depletion in the melt and diffusive water loss from inclusions. Our data suggest that initial water budget is unchanged all over the last 20 years, reflecting therefore a potential in triggering highly explosive eruptions depending on degassing dynamics under open versus closed system conditions at shallow levels.

Northwest Africa (NWA) 8709 is a rare example of a type 3 ordinary chondrite melt breccia and provides critical information for the shock compaction histories of chondrites. An L3 protolith for NWA 8709 is inferred on the basis of oxygen isotope composition, elemental composition, diverse mineral chemistry, and overall texture. NWA 8709 is among the most strongly shocked type 3 chondrites known, and experienced complete melting of the matrix and partial melting of chondrules. Unmelted phases underwent FeO reduction and partial homogenization, with reduction possibly occurring by reaction of olivine and low‐Ca pyroxene with an S‐bearing gas that was produced by vaporization. Chondrules and metal grains became foliated by uniaxial compaction, and during compression, chondrules and fragments became attached to form larger clumps. This process, and possibly also melt incorporation into chondrules to cause “inflation,” may have contributed to anomalously large chondrule sizes in NWA 8709. The melt breccia character is attributed to strong shock affecting a porous precursor. Data‐model comparisons suggest that a precursor with 23% porosity that was impacted by a 3 km/s projectile could have produced the meteorite. The rarity of other type 3 ordinary chondrite melt breccias implies that the immediate precursors to such chondrites were lower in porosity than the NWA 8709 precursor, or experienced weaker shocks. Altogether, the data imply a predominantly “quiet” dynamical environment to form most type 3 ordinary chondrites, with compaction occurring in a series of relatively weak shock events.

The Tissint Martian meteorite is an unusual depleted olivine‐phyric shergottite, reportedly sourced from a mantle‐derived melt within a deep magma chamber. Here, we report major and trace element data for Tissint olivine and pyroxene, and use these data to provide new insights into the dynamics of the Tissint magma chamber. The presence of irregularly spaced oscillatory phosphorous (P)‐rich bands in olivine, along with geochemical evidence indicative of a closed magmatic system, implies that the olivine grains were subject to solute trapping caused by vigorous crystal convection within the Tissint magma chamber. Calculated equilibration temperatures for the earliest crystallizing (antecrystic) olivine cores suggest a Tissint magma source temperature of 1680 °C, and a local Martian mantle temperature of 1560 °C during the late Amazonian—the latter being consistent with the ambient mantle temperature of Archean Earth.

© The Meteoritical Society, 2020. Ureilites are carbon-rich ultramafic achondrites that have been heated above the silicate solidus, do not contain plagioclase, and represent the melting residues of an unknown planetesimal (i.e., the ureilite parent body, UPB). Melting residues identical to pigeonite-olivine ureilites (representing 80% of ureilites) have been produced in batch melting experiments of chondritic materials not depleted in alkali elements relative to the Sun’s photosphere (e.g., CI, H, LL chondrites), but only in a relatively narrow range of temperature (1120 ºC–1180 ºC). However, many ureilites are thought to have formed at higher temperature (1200 ºC–1280 ºC). New experiments, described in this study, show that pigeonite can persist at higher temperature (up to 1280 ºC) when CI and LL chondrites are melted incrementally and while partial melts are progressively extracted. The melt productivity decreases dramatically after the exhaustion of plagioclase with only 5–9 wt% melt being generated between 1120 ºC and 1280 ºC. The relative proportion of pyroxene and olivine in experiments is compared to 12 ureilites, analyzed for this study, together with ureilites described in the literature to constrain the initial Mg/Si ratio of the UPB (0.98–1.05). Experiments are also used to develop a new thermometer based on the partitioning of Cr between olivine and low-Ca pyroxene that is applicable to all ureilites. The equilibration temperature of ureilites increases with decreasing Al2O3 and Wo contents of pyroxene and decreasing bulk REE concentrations. The UPB melted incrementally, at different fO2, and did not cool significantly (0 ºC–30 ºC) prior to its disruption. It remained isotopically heterogenous, but the initial concentration of major elements (SiO2, MgO, CaO, Al2O3, alkali elements) was similar in the different mantle reservoirs.

Lunar breccias preserve the records of geologic processes on the Moon. In this study, we report the occurrence, petrography, mineralogy, and geological significance of the observed secondary olivine veinlets in lunar feldspathic breccia meteorite Northwest Africa (NWA) 11273. Bulk-rock composition measurements shown that this meteorite is geochemically similar to other lunar highland meteorites. In NWA 11273, five clasts are observed to host veinlets that are dominated by interconnecting olivine mineral grains. The host clasts mainly composed of mafic minerals (i.e., pyroxene and olivine) and probably sourced from a basaltic lithology. The studied olivine veinlets (~5 to 30 μm in width) are distributed within the mafic-mineral host, but do not extend into the adjacent plagioclase. Chemically, these olivine veinlets are Fe-richer (Fo41.4–51.9), compared with other olivine grains (Fo54.3–83.1) in lithic clasts and matrix of NWA 11273. By analogy with the secondary olivine veinlets observed in meteorites from asteroid Vesta (HED-group samples) and lunar mare samples, our study suggests that the newly observed olivine veinlets in NWA 11273 are likely formed by secondary deposition from a lunar fluid, rather than by crystallization from a high-temperature silicate melt. Such fluid could be sulfur- and phosphorous-poor and likely had an endogenic origin on the Moon. The new occurrence of secondary olivine veinlets in breccia NWA 11273 reveals that the fluid mobility and deposition could be a previously underappreciated geological process on the Moon.

Among the many ungrouped meteorites, Acfer 370, NWA 7135, and El Médano 301—probably along with the chondritic inclusion in Cumberland Falls and ALHA 78113—represent a homogeneous grouplet of strongly reduced forsterite‐rich chondrites characterized by common textural, chemical, mineralogical, and isotopic features. All of these meteorites are much more reduced than OCs, with a low iron content in olivine and low‐Ca pyroxene. In particular, Acfer 370 is a type 4 chondrite that has olivine and low‐Ca pyroxene compositional ranges of Fa 5.2–5.8 and Fs 9.4–33.4, respectively. The dominant phase is low‐Ca pyroxene (36.3 vol%), followed by Fe‐Ni metal (16.3 vol%) and olivine (15.5 vol%); nevertheless, considering the Fe‐oxyhydroxide (due to terrestrial weathering), the original metal content was around 29.6 vol%. Finally, the mean oxygen isotopic composition Δ17O = +0.68‰ along with the occurrence of a silica phase, troilite, Ni‐rich phosphides, chromite, and oldhamite confirms that these ungrouped meteorites have been affected by strong reduction and are different from any other group recognized so far.

Deep earthquakes, 300 to 700 km deep, have been observed for decades and shown to originate from major mineral transformations occurring at these depths, including phase transitions of olivine and ...

Olivine is the main constituent of the upper mantle, and its phase transformation affects the rheology of the subduction zone. It is crucial to reveal the kinetics of olivine (α)-spinel (γ) phase t...

Perseverance landed at the Octavia E. Butler landing site next to the Seitah dune region in Jezero crater on 18 February 2021, in close proximity...

Mantle transition zone (MTZ) is the layer between two seismic upper mantle discontinuities, which are generally believed to be caused by the transformation of high-pressure polymorphs of olivine oc...

The shergottite family of meteorites shows a remarkable petrographic and geochemical variety, revealing information about mantle processes and basalt formation on Mars. Northwest Africa (NWA) 11115...

Seismic anisotropy produced by aligned olivine in oceanic lithosphere offers a window into mid-ocean ridge dynamics and the state of Earth's upper mantle. Yet, interpreting anisotropy in the contex...

Hydrous phyllosilicate minerals, including the serpentine subgroup, are likely to be major constituents of material that will be bought back to Earth by missions to Mars and to primitive asteroids Ryugu and Bennu. Small quantities (< 60 g) of micrometre sized, internally heterogeneous material will be available for study, requiring minimally destructive techniques. Many conventional methods are unsuitable for phyllosilicates as they are typically finely crystalline and electron beam sensitive resulting in amorphisation and dehydration. New tools will be required for nanoscale characterisation of these precious extra‐terrestrial samples. Here we test the effectiveness of atom probe tomography (APT) for this purpose. Using lizardite from the Ronda peridotite, Spain, as a terrestrial analogue, we outline an effective analytical protocol to extract nanoscale chemical and structural measurements of phyllosilicates. The potential of APT is demonstrated by the unexpected finding that the Ronda lizardite contains SiO‐rich nanophases, consistent with opaline silica that formed as a by‐product of the serpentinisation of olivine. Our new APT approach unlocks previously unobservable nanominerals and nanostructures within phyllosilicates owing to resolution limitations of more established imaging techniques. APT will provide unique insights into the processes and products of water/rock interaction on Earth, Mars and primitive asteroids.

Almahata Sitta (AhS), an anomalous polymict ureilite, is the first meteorite observed to originate from a spectrally classified asteroid (2008 TC(3)). However, correlating properties of the meteorite with those of the asteroid is not straightforward because the AhS stones are diverse types. Of those studied prior to this work, 70–80% are ureilites (achondrites) and 20–30% are various types of chondrites. Asteroid 2008 TC(3) was a heterogeneous breccia that disintegrated in the atmosphere, with its clasts landing on Earth as individual stones and most of its mass lost. We describe AhS 91A and AhS 671, which are the first AhS stones to show contacts between ureilitic and chondritic materials and provide direct information about the structure and composition of asteroid 2008 TC(3). AhS 91A and AhS 671 are friable breccias, consisting of a C1 lithology that encloses rounded to angular clasts (

We performed a petrologic, geochemical, and oxygen isotopic study of the lowest FeO ordinary chondrite, Yamato (Y) 982717. Y 982717 shows a chondritic texture composed of chondrules and chondrule fragments, and mineral fragments set in a finer-grained, clastic matrix, similar to H4 chondrites. The composition of olivine (Fa11.17 ± 0.48 (1σ)) and low-Ca pyroxene (Fs11.07 ± 0.98 (1σ)Wo0.90 ± 0.71(1σ)) are significantly more magnesian than those of typical H chondrites (Fa16.0-20, Fs14.5-18.0), as well as other known low-FeO OCs (Fa12.8-16.7; Fs13-16). However, the bulk chemical composition of Y 982717, in particular lithophile and moderately volatile elements, is within the range of OCs. The bulk siderophile element composition (Ni, Co) is within the range of H chondrites and distinguishable from L chondrites. The O-isotopic composition is also within the range of H chondrites. The lack of reduction textures indicates that the low olivine Fa content and low-Ca pyroxene Fs content are characteristics of the precursor materials, rather than the result of reduction during thermal metamorphism. We suggest that the H chondrites are more compositionally diverse than has been previously recognized.

Silicate minerals represent an important reservoir of nutrients at Earth's surface and a source of alkalinity that modulates long-term geochemical cycles. Due to the slow kinetics of primary silicate mineral dissolution and the potential for nutrient immobilization by secondary mineral precipitation, the bioavailability of many silicate-bound nutrients may be limited by the ability of micro-organisms to actively scavenge these nutrients via redox alteration and/or organic ligand production. In this study, we use targeted laboratory experiments with olivine and the siderophore deferoxamine B to explore how microbial ligands affect nutrient (Fe) release and the overall rate of mineral dissolution. Our results show that olivine dissolution rates are accelerated in the presence of micromolar concentrations of deferoxamine B. Based on the non-linear decrease in rates with time and formation of a Fe3+ -ligand complex, we attribute this acceleration in dissolution rates to the removal of an oxidized surface coating that forms during the dissolution of olivine at circum-neutral pH in the presence of O2 and the absence of organic ligands. While increases in dissolution rates are observed with micromolar concentrations of siderophores, it remains unclear whether such conditions could be realized in natural environments due to the strong physiological control on microbial siderophore production. So, to contextualize our experimental results, we also developed a feedback model, which considers how microbial physiology and ligand-promoted mineral dissolution kinetics interact to control the extent of biotic enhancement of dissolution rates expected for different environments. The model predicts that physiological feedbacks severely limit the extent to which dissolution rates may be enhanced by microbial activity, though the rate of physical transport modulates this limitation.

Seismic-frequency torsional forced-oscillation measurements of shear modulus dispersion and associated strain-energy dissipation under conditions of simultaneously high temperature and pressure in ...

We conducted high‐temperature and high-pressure deformation experiments on hot-pressed aggregates of olivine + 9 wt% dolomite at 1 GPa and 1100oC in a Griggs-type apparatus. At run conditions,...

Transient creep occurs during geodynamic processes that impose stress changes on rocks at high temperatures. The transient is manifested as evolution...

Electron probe microanalyzer measurements of trace elements with high accuracy are challenging. Accurate Al measurements in olivine are required to calibrate SIMS implant reference materials for measurement of Al in the solar wind. We adopt a combined EPMA/SIMS approach that is useful for producing SIMS reference materials as well as for EPMA at the ~100 μg g(−1) level. Even for mounts not polished with alumina photoelectron spectroscopy shows high levels of Al surface contamination. In order to minimize electron beam current density, a rastered 50 × 100 μm electron beam was adequate and minimized sensitivity to small Al-rich contaminants. Reproducible analyses of eleven SIMS-cleaned spots on San Carlos olivine agreed at 69.3 ± 1.0 μg g(−1)• The known Al mass fraction was used to calibrate an Al implant into San Carlos. Accurate measurements of Al were made for olivines in the pallasites: lmilac, Eagle Station and Springwater. Our focus was on Al in olivine, but our technique could be refined to give accurate electron probe measurements for other contamination-sensitive trace elements. For solar wind, it is projected that the Al/Mg abundance ratio can be determined to 6%, a factor of 2 more precise than the solar spectroscopic ratio.