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At least 181 records · Page 10

Extracting Olivine (Fo-Fa) Compositions from Raman Spectral Peak Positions

Olivine and pyroxene are two major basaltic minerals that have been identified at Gusev Crater and Meridiani Planum by the Mars Exploration Rovers. Full petrologic characterization of a sample (rock or soil), however, requires determining the range of mineral compositions, extent of zoning, range of grain sizes, mineral associations, presence of xenocrysts, etc. Information of this sort will aid the interpretation of sample crystallization and differentiation histories and help discriminate between lithologies. In Raman spectroscopic experiments, minerals are identified by their spectral patterns and mineral compositions can be inferred from the peak positions. Instruments currently in use or slated for impending surface exploration missions provide only average elemental compositions for relatively large rock or soil targets or bulk mineral analysis. No techniques currently in use or scheduled for flight can characterize both structure and composition of individual mineral grains, in-situ, like the Mars Microbeam Raman Spectrometer (MMRS). The MMRS is designed to take 100 spectra along a 1 cm linear traverse on the surface of a sample, with contributions from one or a few mineral phases per spectrum. We presented a method to extract structural and compositional information from the Raman spectra of quadrilateral pyroxenes. The pyroxene calibration was applied to a Raman spectroscopic study of Martian meteorite EETA79001 along with a preliminary olivine calibration, where we demonstrated the capability to discriminate related lithologies using Raman point counts. This paper presents an improved olivine calibration that will further aid sample characterization and the study of alteration processes.

Kuebler, K.↗

A Chemical Model of Micrometeorite Impact into Olivine

Laboratory simulations of space weathering using laser irradiation have been successful in reproducing space weathering characteristics such as the reduction of olivine to form nanophase iron particles. However, the chemistry of the reduction of Fe2+ in olivine to Fe metal has not been fully explored. We present a thermodynamic model of olivine undergoing post-impact cooling and decompression.

Sheffer, A. A.↗

Synchrotron X-Ray Diffraction Studies of Olivine from Comet Wild 2

We have analyzed a collection of the Comet Wild 2 coma grains returned by the NASA Stardust Mission, using micro-area Laue diffraction equipment. The purpose of the diffraction experiment is to permit the structure refinement of olivine including site occupancies. In addition to the intrinsic importance of the olivine structures for revealing the thermal history of Wild 2 materials, we wish to test reports that olivine recovered after hypervelocity capture in silica aerogel has undergone a basic structural change due to capture heating [1]. The diffraction equipment placed at beam line BL- 4B1 of PF, KEK was developed with a micropinhole and an imaging plate (Fuji Co. Ltd.) using the Laue method combined with polychromatic X-ray of synchrotron radiation operated at energy of 2.5 GeV. The incident beam is limited to 1.6 m in diameter by a micropinhole set just upstream of the sample [2, 3]. It is essential to apply a microbeam to obtain diffracted intensities with high signal to noise ratios. This equipment has been successfully applied to various extraterrestrial materials, including meteorites and interplanetary dust particles [4]. The Laue pattern of the sample C2067,1,111,4 (Fig. 1) was successfully taken on an imaging plate after a 120 minute exposure (Fig. 2).

Source record↗

Moessbauer Mineralogy of Rock, Soil, and Dust at Gusev Crater, Mars: Spirit's Journey through Weakly Altered Olivine Basalt on the Plains and Pervasively Altered Basalt in the Columbia Hills

The Moessbauer spectrometer on Spirit measured the oxidation state of Fe, identified Fe-bearing phases, and measured relative abundances of Fe among those phases for surface materials on the plains and in the Columbia Hills of Gusev crater. Eight Fe-bearing phases were identified: olivine, pyroxene, ilmenite, magnetite, nanophase ferric oxide (npOx), hematite, goethite, and a Fe(3+)-sulfate. Adirondack basaltic rocks on the plains are nearly unaltered (Fe(3+)/Fe(sub T)<0.2) with Fe from olivine, pyroxene (Ol>Px), and minor npOx and magnetite. Columbia Hills basaltic rocks are nearly unaltered (Peace and Backstay), moderately altered (WoolyPatch, Wishstone, and Keystone), and pervasively altered (e.g., Clovis, Uchben, Watchtower, Keel, and Paros with Fe(3+)/Fe(sub T) approx.0.6-0.9). Fe from pyroxene is greater than Fe from olivine (Ol sometimes absent), and Fe(2+) from Ol+Px is 40-49% and 9-24% for moderately and pervasively altered materials, respectively. Ilmenite (Fe from Ilm approx.3-6%) is present in Backstay, Wishstone, Keystone, and related rocks along with magnetite (Fe from Mt approx. 10-15%). Remaining Fe is present as npOx, hematite, and goethite in variable proportions. Clovis has the highest goethite content (Fe from Gt=40%). Goethite (alpha-FeOOH) is mineralogical evidence for aqueous processes because it has structural hydroxide and is formed under aqueous conditions. Relatively unaltered basaltic soils (Fe(3+)/Fe(sub T) approx. 0.3) occur throughout Gusev crater (approx. 60-80% Fe from Ol+Px, approx. 10-30% from npOx, and approx. 10% from Mt). PasoRobles soil in the Columbia Hills has a unique occurrence of high concentrations of Fe(3+)-sulfate (approx. 65% of Fe). Magnetite is identified as a strongly magnetic phase in Martian soil and dust.

Morris, R. V.↗

Oxygen Fugacity of the Upper Mantle of Mars. Evidence from the Partitioning Behavior of Vanadium in Y980459 (Y98) and other Olivine-Phyric Shergottites

Using partitioning behavior of V between olivine and basaltic liquid precisely calibrated for martian basalts, we determined the redox state of primitive (olivine-rich, high Mg#) martian basalts near their liquidus. The combination of oxidation state and incompatible element characteristics determined from early olivine indicates that correlations between fO2 and other geochemical characteristics observed in many martian basalts is also a fundamental characteristic of these primitive magmas. However, our data does not exhibit the range of fO2 observed in these previous studies.. We conclude that the fO2 for the martian upper mantle is approximately IW+1 and is incompatible-element depleted. It seems most likely (although clearly open to interpretation) that these mantle-derived magmas assimilated a more oxidizing (>IW+3), incompatible-element enriched, lower crustal component as they ponded at the base of the martian crust.

Shearer, C. K.↗

Using the Fe/Mn Ratio of FeO-Rich Olivine In WILD 2, Chondrite Matrix, and Type IIA Chondrules to Disentangle Their Histories

The Stardust Mission returned a large abundance of impactors from Comet 81P/Wild2 in the 5-30 m range. The preliminary examination of just a limited number of these particles showed that the collection captured abundant crystalline grains with a diverse mineralogy [1,2]. Many of these grains resemble those found in chondrite matrix and even contain fragments of chondrules and CAIs [1-3]. In particular, the olivine found in Wild 2 exhibits a wide compositional range (Fa0-97) with minor element abundances similar to the matrix olivine found in many carbonaceous chondrites (CCs) and unequilibrated ordinary chondrites (UOCs). Despite the wide distribution of Fa content, the olivine found in the matrices of CCs, UOCs, and Wild 2 can be roughly lumped into two types based solely on fayalite content. In fact, in some cases, a distinct bi-modal distribution is observed.

Frank, David R.↗

Ar-40/Ar-39 Ages for Maskelynites and K-Rich Melt from Olivine-Rich Lithology in (Kanagawa) Zagami

We report Ar/Ar release patterns for small maskelynite grains and samples of a K-rich phase separated from the basaltic shergottite Zagami. The purpose of the work is to investigate the well-known discrepancy between published Ar/Ar ages of Zagami, >200 Ma, and its age of approx. 170 Ma as determined by other methods [1-6]. Niihara et al. [7] divide less abundant darker material present in Zagami into an olivine-rich lithology (ORL), from which most of our samples came, and a pyroxene-rich one (Dark Mottled-Lithology: DML) [8, 9]. ORL consists of vermicular fayalitic olivine, coarse-grained pyroxene, maskelynite, and a glassy phase exceptionally rich in K (up to 8.5 wt%), Al, and Si, but poor in Fe and Mg. The elemental composition suggests a late-stage melt, i.e., residual material that solidified late in a fractional crystallization sequence. Below we refer to it as "K-rich melt." The K-rich melt contains laths of captured olivine, Ca-rich pyroxene, plagioclase, and opaques. It seemed to offer an especially promising target for Ar-40/Ar-39 dating.

Park, J.↗

Tracking the Martian Mantle Signature in Olivine-Hosted Melt Inclusions of Basaltic Shergottites Yamato 980459 and Tissint

The Martian shergottite meteorites are basaltic to lherzolitic igneous rocks that represent a period of relatively young mantle melting and volcanism, approximately 600-150 Ma (e.g. [1,2]). Their isotopic and elemental composition has provided important constraints on the accretion, evolution, structure and bulk composition of Mars. Measurements of the radiogenic isotope and trace element concentrations of the shergottite meteorite suite have identified two end-members; (1) incompatible trace element enriched, with radiogenic Sr and negative epsilon Nd-143, and (2) incompatible traceelement depleted, with non-radiogenic Sr and positive epsilon 143-Nd(e.g. [3-5]). The depleted component represents the shergottite martian mantle. The identity of the enriched component is subject to debate, and has been proposed to be either assimilated ancient martian crust [3] or from enriched domains in the martian mantle that may represent a late-stage magma ocean crystallization residue [4,5]. Olivine-phyric shergottites typically have the highest Mg# of the shergottite group and represent near-primitive melts having experienced minimal fractional crystallization or crystal accumulation [6]. Olivine-hosted melt inclusions (MI) in these shergottites represent the most chemically primitive components available to understand the nature of their source(s), melting processes in the martian mantle, and origin of enriched components. We present trace element compositions of olivine hosted melt inclusions in two depleted olivinephyric shergottites, Yamato 980459 (Y98) and Tissint (Fig. 1), and the mesostasis glass of Y98, using Secondary Ionization Mass Spectrometry (SIMS). We discuss our data in the context of understanding the nature and origin of the depleted martian mantle and the emergence of the enriched component.

Peters, T. J.↗

Experimental Hypervelocity Dust Impact in Olivine: FIB/TEM Characterization of Micron-Scale Craters with Comparison to Natural and Laser-Simulated Small-Scale Impact Effects

The space weathering of regoliths on airless bodies and the formation of their exospheres is driven to a large extent by hypervelocity impacts from the high relative flux of micron to sub-micron meteoroids that comprise approximately 90 percent of the solar system meteoroid population. Laboratory hypervelocity impact experiments are crucial for quantifying how these small impact events drive space weathering through target shock, melting and vaporization. Simulating these small scale impacts experimentally is challenging because the natural impactors are both very small and many have velocities above the approximately 8 kilometers-per-second limit attainable by conventional chemical/light gas accelerator technology. Electrostatic "dust" accelerators, such as the one recently developed at the Colorado Center for Lunar Dust and Atmospheric Studies (CCLDAS), allow the experimental velocity regime to be extended up to tens of kilometers-per-second. Even at these velocities the region of latent target damage created by each impact, in the form of microcraters or pits, is still only about 0.1 to 10 micrometers in size. Both field-emission analytical scanning electron microscopy (FE-SEM) and advanced field-emission scanning transmission electron microscopy (FE-STEM) are uniquely suited for characterizing the individual dust impact sites in these experiments. In this study, we have used both techniques, along with focused ion beam (FIB) sample preparation, to characterize the micrometer to nanometer scale effects created by accelerated dust impacts into olivine single crystals. To our knowledge this work presents the first TEM-scale characterization of dust impacts into a key solar system silicate mineral using the CCLDAS facility. Our overarching goal for this work is to establish a basis to compare with our previous results on natural dust-impacted lunar olivine and laser-irradiated olivine.

Christoffersen, R.↗

The Effect of Redox Conditions on Seismic Waves in Iron-Bearing Olivine: Implications for Understanding Planetary Interiros Through Seismilogy

Seismic data, inclusive of velocities and attenuation, can be utilized to elucidate the physical state of planetary interiors]. However, numerous micromechanical factors have been either experimentally demonstrated, or theoretically considered, to affect the propagation and dissipation of seismic energy within crystalline solids - including, but not limited to, changes in grain size, temperature, melt fraction, pressure and dislocation density. Thus, observed variations in seismic wave speeds and attenuation may be used to ultimately ‘map’ variations in physical properties, such as those listed above, within planetary bodies. But, in order to complete a successful inversion of seismic data into representations of physical properties, a first requirement is to obtain a fundamental laboratory based understanding of how each of these possible factors individually influences seismic waves. Here we conduct an experimental study with the initial objective to further understand one of the most commonly invoked, yet least studied, mechanisms that could alter intrinsic seismic wave attenuation: water content (occurring as chemically-bound hydroxyl). The historical basis for determining the effect of water on seismic properties was established predominantly through analogy with large-strain creep experiments conducted on olivine under water-saturated conditions. While these deformation experiments routinely demonstrate a weakening of olivine in the presence of water, they represent a fundamentally different deformation regime in comparison to the microstrains experienced due to a passing seismic wave. Thus, in order to directly assess the effects of water on seismic properties, small-strain experiments are required. Substantially modified seismic properties in the presence of water have been observed previously at low strains and low frequencies, but only in a single exploratory study conducted under water-saturated conditions. Thus, to properly test the theoretical predictions we conducted a systematic study of the seismic properties of olivine using low-frequency torsional oscillation on aggregates containing varying concentrations of bound hydroxyl, for the first time at under saturated conditions.

Cline, C. J., II↗

Martian Magma Evolution from Olivine-Hosted Melt Inclusions in Shergottites Using MELTS Models

Shergottites, the largest martian meteorite group, come from at least two geochemically different source reservoirs i.e. incompatible trace element (ITE)-depleted and enriched. The depleted shergottites are thought to be derived from an ITE-depleted mantle reservoir, while enriched shergottites are thought to be derived from an ITE-enriched mantle reservoir that represents late stage residual melt from a magma ocean or interaction with martian crust. Moreover, the martian crust is distinct from shergottites, by being highly oxidized, distinctly ITE-enriched, and older. The link between the crust and shergottite compositions is poorly understood. Here we model shergottite differentiation to resolve the origin of enriched shergottites and why the bulk martian crust is compositionally distinct from shergottites. Early formed olivine-hosted melt inclusions can provide primary melt composition from which the parental magma had crystallized and also information at different stages of crystallization during parent magma differentiation that leads to shergottite magma evolution as well as crustal contribution assessment. We analyzed olivine-hosted melt inclusions of two enriched poikilitic shergottites for their major, minor and trace element concentrations using electron microprobe and laser ablation ICP-MS. We corrected the melt inclusion compositions for post-entrapment re-equilibration with their host olivine. To comprehend the crystallization sequence of these rocks and whether the melt entrapment is consistent with the crystallization, we use MELTS models for equilibrium and fractional crystallization. The results of these models suggest that all the melts were trapped in a closed system progressive crystallization at 1150-1210 ⁰C within 1 kbar to 1 bar pressure that is equivalent to <8.5 km, implying melt entrapment without any additional exogenous materials.

Ferdous, J.↗

Olivine Compositional Variation of Asteroid Ryugu Samples: Possible Precursors of Ryugu’s Parent Asteroid

JAXA’s Hayabusa2 spacecraft successfully recovered samples from Cb-type asteroid Ryugu and returned samples are now under detailed scrutiny by the international community. The ongoing initial analysis has so far revealed that the Ryugu samples are pristine primitive asteroidal materials mostly composed of secondary minerals such asphyllosilicates, carbonates, Fe sulfides and magnetite associated with organic matter [e.g., 1]. However, some samples contain small amounts of anhydrous silicates and oxides such as olivine that are thought to be the precursors of the Ryugu parent asteroid. Their sizes are mostly <5 mm, and detailed mineralogical analysis is possible using an electron microprobe with field emission gun (FE-EPMA). Here we report results of our extensive FE-EPMA analysis of an hydrous minerals focusing on olivine to compare with literature chondritic data. We also performed synchrotron XRD of olivine crystals to evaluate the shock degree of Ryugu samples. These analyses allow us to discuss the formation of Ryugu in light of the solar system early evolution.

T Mikouchi↗

A Komatiite Succession as an Analog for the Olivine Bearing Rocks at Jezero

The Mars 2020 rover landed at Jezero crater on February 18, 2021 [1]. Since then, the rover has traveled around the “Séítah” region [2] and has collected data from the Mastcam-Z, Supercam, PIXL and SHERLOC instruments that has led to insights into the formation of the olivine-clay-carbonate bearing rocks that were identified from orbit [3,4]. Here we discuss three questions: 1) What have we learned about the olivine-claycarbonate unit? 2) What terrestrial analogs exist for the unit? 3) Why do the rocks have a thinly layered morphology? We shall briefly mention instrumental measurements which provide important information regarding the olivine bearing rock at Seitah. Note: Extended abstract included on attachment.

A.J. Brown↗

Olivine Mineralogy of Asteroid Ryugu Samples and CI Chondrites: Further Evidence for their Common Origin

Initial analysis of asteroid Ryugu samples has revealed that they were mm-mm scale brecciamostly composed of aqueously altered phases (e.g., Mg-Fe phyllosilicates, carbonates) and showed remarkablesimilarities to CI chondrites in mineralogy and chemistry [e.g., 1,2]. Our detailed analysis of Ryugu samples hasdetected small amounts (<<1 vol.%) of unaltered silicates that would escape severe aqueous alteration [3]. Olivine isthe most abundant (>90 vol%) phase among such unaltered silicates. Although most Ryugu olivine grains aresmaller than 5 mm, they bear important information about the precursors of the parent Ryugu asteroid. In thisabstract we report additional results of olivine mineralogical study of Ryugu samples, and especially compare witholivine grains in CI chondrites (Ivuna and Orgueil) to further discuss their relationship and possible common origin.

T. Mikouchi↗

The Role of Olivine in Fe-Carbonate Formation in Gale Crater, Mars

Carbonates have been identified in remote sensing datasets, martian meteorites, and in-situ with rovers at Gale and Jezero craters. In Gale crater, traces of carbonate have been found by the SAM instrument throughout the Mars Science Laboratory mission, e.g., at Rocknest and Pahrump Hills, with models for carbonate formation at Pahrump Hills explored by [9]. Further up-section, CheMin data of clay-rich Glen Torridon (GT) samples show that five out of seven drill samples from GT contain Fe-carbonate alongside phyllosilicates. The GT sediments were deposited in a lacustrine environment and subsequently underwent multiple episodes of diagenesis. In this work, we explore the role of olivine in the formation of carbonates by modelling the interaction of different martian olivines with a previously modeled Gale groundwater. We then explore the incongruent dissolution of host rocks within the GT sediments by mixing olivine with quantities of the Kilmarie drill sample chemical composition as the reactant rock.

S M R Turner↗

A common isotopic reservoir for amoeboid olivine aggregates (AOAs) and calcium-aluminum-rich inclusions (CAIs) revealed by Ti and Cr isotopic compositions

Amoeboid olivine aggregates (AOAs) are the most abundant type of refractory inclusions found in most carbonaceous chondrite groups. AOAs are thought to be genetically related to calcium-aluminum-rich inclusions (CAIs) and potential chondrule precursor components, although the precise physical and temporal details of AOA formation and their relationship to other chondritic components remain unclear. In this study, we measured the chromium and titanium isotopic compositions of eight AOAs from four different CV chondrites with the goal of evaluating potential genetic links between AOAs, CAIs, and chondrules. These are the first Cr and Ti isotopic data reported beyond a single AOA previously measured for Cr and a different single AOA previously measured for Ti. The results presented here show that the ε 54 Cr and ε 50 Ti isotopic compositions of AOAs are indistinguishable from those of CAIs, suggesting that AOAs and CAIs formed from a common region of the disk. Here, we also demonstrate, based on the comparison of the Cr and Ti isotopic composition of AOAs to previously measured chondrules, that mixing between AOAs and an NC compositional endmember alone cannot fully explain the range of measured chondrule compositions. Although AOAs may have been important chondrule precursor components along with AOA olivine, CAIs, fragments of earlier generation chondrules, and fine-grained matrix material, this observation requires another currently unknown component to be involved in chondrule formation.

58 GEOSCIENCES↗

Computer simulation of reaction and transport of core-scale serpentinization of Fe-bearing olivine and evolution of geological hydrogen

We present reactive flow and transport simulations of core-scale serpentinization of forsteritic, Fe-bearing olivine under hydrothermal conditions. The model captures fluid flow, evolving porosity–permeability, and redox-controlled H 2 production in a cylindrical core over 55 days at 245 °C and 37 bar. Key processes include olivine dissolution, precipitation of serpentine and magnetite, and oxidation of Fe2+ to Fe 3+ . Here, results show strong coupling among flow velocity, alteration front propagation, and spatially heterogeneous H 2 generation. Elevated H2 concentrations align with inlet-localized magnetite precipitation, consistent with experiments. Secondary mineral formation reduces porosity and permeability, altering transport pathways. Reactive flow at the fluid–solid interface governs H 2 generation rates and distribution. Dissolved SiO2 promotes serpentine and talc formation by suppressing brucite, while bicarbonate extends reaction duration and moderates surface complexation effects.

Geologic hydrogen↗

Dislocation theory of steady and transient creep of crystalline solids: Predictions for olivine

In applications critical to the geological, materials, and engineering sciences, deformation occurs at strain rates too small to be accessible experimentally. Instead, extrapolations of empirical relationships are used, leading to epistemic uncertainties in predictions. To address these problems, we construct a theory of the fundamental processes affecting dislocations: storage and recovery. We then validate our theory for olivine deformation. This model explains the empirical relationships among strain rate, applied stress, and dislocation density in disparate laboratory regimes. It predicts the previously unexplained dependence of dislocation density on applied stress in olivine. The predictions of our model for Earth conditions differ from extrapolated empirical relationships. For example, it predicts rapid, transient deformation in the upper mantle, consistent with recent measurements of postseismic creep.

36 MATERIALS SCIENCE↗