Calcic Pyroxene Research Articles

Compositional variation and petrogenesis of mare basalts in the Humorum basin: New insights from spectral analysis and crater counting

Pyroxene chemistry estimated using a series of spectral parameters derived from Chandrayaan-I M3 data was used to divide the basalts of Mare Humorum into six compositional units. In order to understand the petrogenetic history of the Humorum basalts, first, the dominant pyroxene end-member composition in each unit is used to estimate the temperature of crystallization; and then crater counting is implemented using craters mapped from the high-resolution Kaguya Terrain Camera data to estimate the age of each unit. The spatial distributions of pyroxene composition and corresponding crystallization temperatures indicate that there is a difference in volcanic activity between the regions corresponding to Units 1–3 (Group I) and the regions corresponding to Units 4–6 (Group II). This observation is further reinforced by analyzing the variation of FeO and TiO2 content across the units. Hence two sources titanium-rich high calcic pyroxene (HCP) and less titanium high calcic pyroxene (HCP) correspond to two groups of basalts in the Humorum area. Furthermore, our new crater-counting analysis reveals that the magmatic activity probably continued until ca. 1.9 Ga in the Humorum basin. To the best of our knowledge, this younger age of volcanism has not been reported before.

How is carbonate crust digested by magma?

Magma’s volatile budget depends on deep magmatic sources, the degree of differentiation and degassing conditions, and volatile input from the assimilated crust. It is, therefore, important to know the exact mechanism by which the crust is assimilated into magma to understand volatile budgets and eruption behavior. To explore reactions between carbonate, calc–silicate, or skarn xenoliths and basaltic andesite magma, we studied ten calc–silicate xenoliths from the 1994, 1998, 2006, and 2010 Merapi eruptions and four sediment samples of local Javanese carbonate crust. An in situ electron probe microanalysis of the 1994–2010 calc–silicate xenolith minerals and glasses suggests that calcite is a minor and metastable mineral phase in association with wollastonite. In addition, carbonate melts quenched to calcic glasses (32 ± 7 wt% SiO2; 38 ± 3 wt% CaO), similar to experimental glasses produced by crust–melt interaction experiments. Thermodynamic modeling using rhyolite MELTS (version 1.2.0) predicts the production of highly silicic (up to ∼84 wt% of SiO2) and CaO-rich (up to ∼25 wt%) melts during partial melting of calc–silicate material. The observed mechanism of calc–silicate xenolith assimilation is the generation of highly silicic (77 ± 4 wt% of SiO2) melts in association with idiomorphic diopside [Wo49En29; 57 ± 3 Mg# = Mg/(Mg+Fe2+)] and other calcic pyroxenes (Wo54-82 En2-21; 16–43 Mg#) due to partial melting of xenolith and incongruent dissolution reactions. We hypothesize that the rate-limiting process is the subsequent mixing of the produced crustal melts with representative resident andesitic melt (average 65 wt% SiO2) through chemical diffusion, which explains major and volatile (Cl) element contents in the Merapi glass products. In addition to high Sr contents and radiogenic 87Sr/86Sr and elevated CO2, Ba, Co, Cr, Cu, V, Zn, and Zr contents in the magmatic minerals and associated glasses, the recrystallized and residual metamorphic sphene, quartz, garnet, and apatite predicted by rhyolite-MELTS or Magma Chamber Simulator modeling during wallrock melting and residual metastable calcite and wollastonite are important tracers of calc–silicate crust assimilation. The disequilibrium process of calc–silicate crustal assimilation can, thus, be well predicted by dissolution experiments and thermodynamic modeling using rhyolite-MELTS or Magma Chamber Simulator. The rate of calc–silicate crustal assimilation is still unconstrained without adequate high-temperature kinetic time-series experiments. We predict that the crustal assimilation rate is controlled by the Si–Al diffusion and associated convection in the hydrous silicate magma.

Chronology, composition, and mineralogy of mare basalts in the junction of Oceanus Procellarum, Mare Imbrium, Mare Insularum, and Mare Vaporum

The timeline of volcanic activity is critical for constraining the thermal evolution of the Moon. The spatial extents of mare basalts, major products of lunar volcanism, have been precisely extracted from LROC (Lunar Reconnaissance Orbiter Camera) image mosaics. With the maria extents newly extracted from LROC mosaics, we found that a large area of mare basalts in the junction of Oceanus Procellarum, Mare Imbrium, Mare Insularum, and Mare Vaporum (the PIV region) has not yet been dated. This study analysed the chronology, composition, and mineralogy of the PIV region, aiming to finish the picture of basaltic volcanism in the Procellarum region, which is a key puzzle of our global geological mapping of the Moon. According to the topographical, spectral, and compositional characteristics, mare units of the PIV region are defined, and the crater size frequency distribution is measured. The primary craters with diameters >0.1 km in the PIV region are measured, and the absolute model ages of basalt units between ∼3.78 Ga and ∼1.71 Ga are derived. Most western PIV basalt units are Eratosthenian-aged, while eastern units mostly formed in the Imbrian period. The spectra of 4965 small impact craters are extracted to interpret the mineral compositions of the PIV basalt units using Chandrayaan-1 Moon Mineralogy Mapper data. Using a Modified Gaussian Model, the reflectance spectra are deconvoluted, and the obtained modal proportions of mafic minerals show low olivine and high low-Ca pyroxene abundances in the eastern PIV region, while the western region features high olivine and calcic pyroxene concentrations. Three episodes of volcanic events occurring in the PIV region are identified. The first (main) occurred at approximately 3.5 Ga (Late Imbrian), with erupted lava flows with less evolved compositions covering most of the PIV area. The peak of volcanic activity in the Eratosthenian period occurred around 2.5 Ga, where mare basalts with moderately evolved compositions and mineralogy were formed. The last major eruption occurred at approximately 1.8 Ga, forming mare basalts with highly evolved compositions.

Orbital Observations of a Marker Horizon at Gale Crater

AbstractA dark‐toned, indurated, smooth horizon, and (or) bed (herein called “marker horizon”) is exposed across much of the northwestern, southwestern, and southeastern portions of Mount Sharp in Gale crater. Compact Reconnaissance Imaging Spectrometer for Mars spectra taken from the marker horizon exhibit evidence for the presence of high calcium pyroxene and other basaltic minerals in contrast to the hydrated sulfate signatures associated with strata above and below it. Mean dips for the marker horizon and sulfate‐bearing strata are 1–5° with almost all azimuths radially away from the center of Mount Sharp. The marker horizon thickness varies between <1 and 3 m and its elevation changes by 1.6 km across the mound. Surface slopes along the sulfate‐bearing strata above and below the marker horizon are typically 20°–40° compared to <5° surface slopes on the marker horizon. Features observed on the marker horizon include ridges, fractures, faults, layering, oval depressions, small craters, and possible yardangs/indurated bedforms. We interpret the marker horizon to be a single unit that formed contemporaneously across Mount Sharp during the same depositional sequence that created the sulfate‐bearing strata. Plausible formation mechanisms for the marker horizon include (1) emplacement of a more indurated sulfate unit, either from (a) primary deposition or (b) secondary diagenesis; (2) deposition of a more resistant sandstone unit during a brief drier period; (3) emplacement of a volcanic ash deposit laid down in the midst of the sulfate formation period; or (4) a lag deposit created during a drier period. Based on our observations, origins (1a) and (3) are the most plausible.

Compositional and morphological analysis of Gassendi crater

Gassendi impact crater is located on the western side of the visible lunar hemisphere just north of Mare Humorum. It has a diameter of 110 km, and it is a Floor Fractured Crater (FFC) belonging to Class-3 type that exhibits a wide annular depression or moat. Is Gassendi crater formed due to igneous intrusion or viscous relaxation? To investigate this, the analysis explores the compositional and morphological dimensions of the crater. The area studied has been found to contain various minerals such as LCP (Low Calcium Pyroxene), HCP (High Calcium Pyroxene), olivine, plagioclase, and mixtures of pyroxene and plagioclase. To differentiate between similar spectral profiles, Integrated Band Depth map (IBD) and Band Depth Parameter (BD) maps are generated using the M3 data. Features such as central peak complex, isolated mound, fractures, rimae, wall terraces, wall slumps, etc., have been identified and marked in the morphological map. We have also studied the morphometrical aspects of all the morphological features. Another impact crater just on the northern rim of Gassendi, Gassendi A crater shows the presence of LCP and olivine mineral along with extensive slumping, melt pool, and distorted northern rim. We have mapped the three mare regions towards the south of the crater floor and estimated their ages by using the CSFD technique. The present appearance of the Gassendi crater is mostly due to past volcanic activities rather than the result of the impact event.

Strusky z redukční tavby pelosideritové železné rudy realizované na hradě Buchlově (jv. Chřiby) v roce 2019: extrémní variabilita fázového složení a chemismu jednotlivých fází

During experimental smelting of iron in a replica of historical shaft furnace, which was held at the Buchlov Castle in 2019, charcoal and fresh pelosiderite iron ore from the locality Moravany near Kyjov were used. The obtained furnace slag is practically completely formed by glass phase; only rare small domains contain also crystalline phases, whose occurrence is very irregular. A detailed study of chemical composition showed extreme heterogeneity in composition of glass and most crystalline phases. The glass phase contains variable, but often high amounts of Mn, Ca, Mg and sometimes P and/or K. The composition of olivine ranges widely among fayalite, dicalciumsilicate and tephroite (Fa1-91 Fo3-28Te2-45DCS1-52), as well as those of calcic pyroxene (Wo37-60Tsch1-13Ka8-22Fs4-30En14-36). Feldspars showed compositions between orthoclase and anorthite (Or2-82An9-91Ab5-19Cn0-2Slw0-2), which are unknown from natural systems. Minor components include wüstite, melilite (åkermanite with 1 - 6 mol. % gehlenite), leucite, kalsilite, locally also apatite and an unnamed phase with composition close to Ca2Al2Si3O11. The produced metallic iron is also compositionally heterogeneous and rich in phosphorus. The phase composition of slag differs significantly from those of typical iron slags. The reason can be seen in anomalous chemical composition of used ore, in too high temperatures during smelting (phase relations in metallic iron suggest temperatures around 1500 °C) in combination with rapid cooling of the furnace content after finishing of smelting, and probably also higher viscosity of slag melt. Both phase composition of slag as well as chemical composition of individual slag phases and metallic iron are significantly different from those of local historical artefacts from the period of usage of technology of direct production of iron. These findings do not support the idea that local pelosiderite iron ores were used for production of iron already during this early period.

Mineralogy, Geochemistry and Raman Spectroscopy of Multi-Genesis Serpentine Polymorphs of Darepahn Ophiolites

The present article pays to some Alpine-Himalayan ophiolites of Late Cretaceous age from Darepahn area in the southern part of Nain-Baft Ophiolite belt. Whole rock processed data clearly shows that the metaperidotite rocks are silica-poor with low CaO, Al2O3, and TiO2 that reflect the predominance of olivine over calcic pyroxene in the protolithes. The considerable content of Co (85.6–124.6 ppm) and very low contents of Sc (4.3–15.3 ppm) and Sr (0.7-14 ppm) provided more evidence for olivine enrichment in the rock parentages. Calculating numbers of cation per formula unites based on EMPA results for distinguished Serpentine polymorphs (classified structurally via Raman spectroscopy) display that Tschermak substitution of trivalent cations for lizardite is tetrahedrally, and for chrysotile and antigorite, it is octahedrally. These chemical differentiations, lead to identifying chemical field plots in separator diagrams between SiO2, MgO, H2O, and Al2O3. Lizardite polymorphs can consider as primarily metasomatism results thru an iron-rich fluid occurrence. It has a considerable occupation of trivalent cations (especially Fe3+) and simultaneous less than 4 Si atoms in formula structure that reflected tetrahedral Tschermak substitutions. Antigorites have some deformed recrystallized textures along with high Σoct (Total Octahedral Cations) and low H2O content that could be considered as thermal originated polymorph. Chrysotiles have bimodal MgO and FeO contents that return to magnetite formations in groundmass and octahedral Tschermak substitutions on late-stage veins. The results exemplify compositional variations of Darepahn Serpentine polymorphs as a function of textural behaviors, structural position and thermodynamic condition of the formation process.

Aqueous alteration of pyroxene in sulfate, chloride, and perchlorate brines: Implications for post-Noachian aqueous alteration on Mars

Abstract Both high and low calcium pyroxene minerals have been detected over large portions of the martian surface in addition to widespread salts in martian soils and dust. Calcium pyroxenes in martian meteorites are associated with secondary evaporite phases, including sulfates, chlorides, and perchlorates, suggesting the pyroxene may have been altered in saline solutions. Therefore, understanding pyroxene mineral weathering in high salinity brines may provide insight into past aqueous alteration on Mars. This study examines both solute-based dissolution rates and qualitative assessments of weathering textures developed during pyroxene-brine alteration experiments to link dissolution rates and textures and aid in interpreting weathering features observed in Mars meteorites and future pyroxene samples returned from Mars. Batch reactor dissolution experiments were conducted at 298 K to compare diopside (a high Ca-pyroxene) dissolution rates in water (18 MΩ cm−1 ultrapure water (UPW); activity of water (ɑH2O) = 1.0), 0.35 mol kg−1 NaCl (ɑH2O = 0.99), 0.35 mol kg−1 Na2SO4 (ɑH2O = 0.98), 2 mol kg−1 NaClO4 (ɑH2O = 0.90), 2.5 mol kg−1 Na2SO4 (ɑH2O = 0.95), 5.7 mol kg−1 NaCl (ɑH2O = 0.75), and 9 mol kg−1 CaCl2 (ɑH2O = 0.35) brines at pH 5–6.6 to determine how changing solution chemistry and activity of water influence pyroxene dissolution. Aqueous Si release rates and qualitative textural analyses indicate diopside dissolution rates are influenced by both solution chemistry and activity of water, with diopside weathering increasing along a trend from: 9 mol kg−1 CaCl2

Petrogenesis of A-type granites associated with Sn–Nb–Zn mineralization in Ririwai complex, north-Central Nigeria: Constraints from whole-rock Sm[sbnd]Nd and zircon Lu[sbnd]Hf isotope systematics

We report a combined study of whole-rock major- and trace-element geochemistry, SmNd isotope composition, zircon U/Pb dating, and LuHf systematics of peralkaline and aluminous A-type granites from the Ririwai Ring Complex in north-central Nigeria. The Ririwai peralkaline and aluminous A-type granites are strongly ferroan, alkalic to alkali-calcic, and enriched in Hf, Zr, Ga, Rb, Y and REEs. They were emplaced between 176 ± 2.3 Ma and 169.6 ± 0.75 Ma. The peralkaline granites yield relatively higher ɛNd(t) (−2.3 to −1.2) and zircon ɛHf(t) values (−5.8 to −1.7) than the aluminous granites (ɛNd(t) = −3.6 to −3.3; zircon ɛHf(t) = −7.8 to −2.4). In addition, inherited zircons in the aluminous granites yield Pan-African (~590 Ma) ages and low ɛHf(t) values (−14.0). Taken together, these data suggest that the granites formed from extensive fractional crystallization of a transitional basaltic melt derived from an enriched OIB mantle source. The depletions of MgO, CaO, Ti2O, Sr and Ba in the granites indicate that Mg-rich olivine, calcic pyroxene, calcic amphibole, feldspars and FeTi oxides were the major fractionated phases during magma evolution. In addition, several types of evidence, e.g., moderately negative ɛNd(t) and ɛHf(t) values, and the presence of inherited zircons, imply that the parental melt was modified by assimilation of Pan-African upper crust into which the granites were emplaced. A transtensional regime generated prior to late Jurassic breakup of Gondwana, which led to reactivation of shear zones and opening of associated transcurrent faults, paved the way for emplacement of the A-type suite. The Sn–Nb–Zn mineralization of the Ririwai A-type suite was probably linked to complex magmatic evolutionary processes involving extensive fractional crystallization coupled with crustal assimilation and late-stage hydrothermal fluid activity.

Utilisation of wood ash from biomass for the production of ceramic products

Utilisation of biomass as fuel is very attractive from the ecological point of view. Such way of energy extraction is ecologically clean (zero CO2 emission) and biomass is renewable and theoretically inexhaustible local energy source. However, during the utilisation of secondary raw materials of biomass for energy production, higher amount of ash accumulates. Wood ash analysed in the research consists of two types of particles: first type – nonflammable mineral particles consisting of the following main elements: Si, Ca, Fe, O and C (86%) and the main elements of the particles of second type are C and O (98%). The aim of the research is to analyse the possibility to utilise wood ash from biomass for the production of ceramic products. Formation masses are prepared by incorporating from 5% to 60% of wood ash additive and burned at various temperatures. It is identified that this additive influences the properties of ceramic body, i.e. reduces drying and burning shrinkage, density, compressive strength, thermal conductivity, increases water absorption and porosity. Additive of wood ash from biomass influences the ceramic body as a natural pigment that brightens the ceramic body. Colour change is determined by sufficient amounts of calcium pyroxene in the composition thereof iron is inserted.

The role of particle size in the laboratory reflectance spectra of pyroxenes: The case of the 670-nm minor feature

Reflectance spectroscopy is a very helpful tool for remote sensing investigations and has been widely used in terrestrial as well as planetary observations to study the surface composition. From this perspective, the visible (Vis) and near-infrared (NIR) regions of the spectrum, where several diagnostic absorption features of minerals are located, are well suited for the identification of such materials, in particular of rock-forming silicates. Among them, pyroxenes, which have been discovered on the surface of a number of different solar system bodies, play an important role.Up to now, both laboratory and remote sensing spectroscopic studies have been focused mainly on the two major bands at about 1 and 2µm (the so-called Band I and Band II, respectively), while little attention has been paid to the minor bands falling in the visible range. One of the most important of them, present in many pyroxenes as well as in olivines, is the weak feature (reflectance minimum) near 670nm, generally characterized by its variable wings (reflectance maxima) at about 570nm and 720nm. The intensity and the exact position of this feature depend on the type of pyroxene as well as on the grain size of the particles under consideration.In this work we present the Vis/NIR experimental reflectance spectra concerning enstatite and diopside, which are excellent representative of Low Calcium Pyroxenes (typically orthopyroxenes), and High Calcium Pyroxenes (typically clinopyroxenes) respectively. The results are very interesting and show a good correlation between the grain size of our samples and the relative intensities of the reflectance maxima occurring on both sides of the 670nm feature. A similar study performed on Acfer 353, a pyroxene-rich eucritic meteorite of the Howardite–Eucrite–Diogenite family, of putative Vestan origin, shows that also in this case the variability in the Vis region of the spectra is linked to the grain size of the meteoritic particles. The connection between grain size and the behavior of the 670nm feature can potentially be used to derive the average dimension of the regolith existing on the surface of planets and minor bodies.Both laboratory and observational study of the minor features, frequently ignored in the interpretation of the spectra acquired in remote sensing, can give complementary and useful information and thus can definitely contribute to a better knowledge of the mineralogy of planetary and asteroidal surfaces.

The central uplift of Ritchey crater, Mars

Ritchey crater is a ∼79km diameter complex crater near the boundary between Hesperian ridged plains and Noachian highland terrain on Mars (28.8°S, 309.0°E) that formed after the Noachian. High Resolution Imaging Science Experiment (HiRISE) images of the central peak reveal fractured massive bedrock and megabreccia with large clasts. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectral analysis reveals low calcium pyroxene (LCP), olivine (OL), hydrated silicates (phyllosilicates) and a possible identification of plagioclase bedrock. We mapped the Ritchey crater central uplift into ten units, with 4 main groups from oldest and originally deepest to youngest: (1) megabreccia with large clasts rich in LCP and OL, and with alteration to phyllosilicates; (2) massive bedrock with bright and dark regions rich in LCP or OL, respectively; (3) LCP and OL-rich impactites draped over the central uplift; and (4) aeolian deposits. We interpret the primitive martian crust as igneous rocks rich in LCP, OL, and probably plagioclase, as previously observed in eastern Valles Marineris. We do not observe high-calcium pyroxene (HCP) rich bedrock as seen in Argyre or western Valles Marineris. The association of phyllosilicates with deep megabreccia could be from impact-induced alteration, either as a result of the Richey impact, or alteration of pre-existing impactites from Argyre basin and other large impacts that preceded the Ritchey impact, or both.

Experimental investigation of condensation predictions for dust-enriched systems

Condensation models describe the equilibrium distribution of elements between coexisting phases (mineral solid solutions, silicate liquid, and vapor) in a closed chemical system, where the vapor phase is always present, using equations of state of the phases involved at a fixed total pressure (<1bar) and temperature (T). The VAPORS code uses a CaO–MgO–Al2O3–SiO2 (CMAS) liquid model at T above the stability field of olivine, and the MELTS thermodynamics algorithm at lower T. Quenched high-T crystal+liquid assemblages are preserved in meteorites as Type B Ca-, Al-rich inclusions (CAIs), and olivine-rich ferromagnesian chondrules. Experimental tests of compositional regions within 100K of the predicted T of olivine stability may clarify the nature of the phases present, the phase boundaries, and the partition of trace elements among these phases. Twenty-three Pt-loop equilibrium experiments in seven phase fields on twelve bulk compositions at specific T and dust enrichment factors tested the predicted stability fields of forsteritic olivine (Mg2SiO4), enstatite (MgSiO3), Cr-bearing spinel (MgAl2O4), perovskite (CaTiO3), melilite (Ca2Al2SiO7–Ca2Mg2Si2O7) and/or grossite (CaAl4O7) crystallizing from liquid. Experimental results for forsterite, enstatite, and grossite are in very good agreement with predictions, both in chemistry and phase abundances. On the other hand the stability of spinel with olivine, and stability of perovskite and gehlenite are quite different from predictions. Perovskite is absent in all experiments. Even at low oxygen fugacity (IW-3.4), the most TiO2-rich experiments do not crystallize Al-, Ti-bearing calcic pyroxene. The stability of spinel and olivine together is limited to a smaller phase field than is predicted. The melilite stability field is much larger than predicted, indicating a deficiency of current liquid or melilite activity models. In that respect, these experiments contribute to improving the data for calibrating thermodynamic models including MELTS.

Island Arc Origin for the Gladesville and Associated Bodies in the Carolina Superterrane in Central Georgia, Southern Appalachians

Terrestrial mafic and ultramafic bodies form in various tectonic settings and from a wide variety of magma types. Clarifying the origin of such rocks in orogenic belts such as the southern Appalachians is important to understanding the formation of mountain belts and associated mafic and ultramafic rocks. A petrographic and geochemical study was conducted on the Gladesville, Hillsboro, Juliette, Holly Grove, and Berry Creek bodies in the Carolina superterrane of the southern Appalachians in central Georgia to place some constrains on the origin and tectonic setting of these mafic and ultramafic rocks. Results from this study show that the rock types investigated in the Gladesville and associated bodies are mostly metabasalts and olivine metagabbronorites. The mineralogies of these bodies are plagioclase, hornblende, clinopyroxene, and opaques. MgO contents range from 3.5 to 7.5 wt% MgO for the Gladesville, Hillsboro, and Berry Creek bodies, with the Juliette and Holly Grove bodies having slightly higher MgO concentrations, ranging from 11.8 to 12.4 wt%. CaO contents of samples from all the bodies range from 6.9 to 18.1 wt%. Concentrations of trace elements, including Ni and Cr, in all the bodies range from 6 to 224 ppm and from 17 to 1932 ppm, respectively, generally akin to those of tholeiitic basalts. Plagioclase mineral compositions vary widely: the Gladesville body is characterized by plagioclase with An75.1 to An95.7, whereas the Hillsboro body has plagioclase with anorthite compositions of An46.2–69.8. Other bodies, such as the Juliette and Holly Grove bodies, are highly calcic, with plagioclase content ranges of An96.6–99.8 and An90.8–96.9, respectively. Amphiboles from the investigated bodies are tschermakite, magnesiohornblende, and pargasite, and they plot within the range of amphiboles from island arcs and ophiolite complexes. Calcic pyroxenes vary from body to body: Juliette (Ca38.5–50.9Mg54.2–44.9Fe7.2–4.2) through Holly Grove (Ca47.1–49.4Mg43.2–41.2Fe9.7–9.4) to Gladesville (Ca48.9–52.5Mg41.4–42.5Fe9.7–5.2). Both spider diagrams, which show Nb depletions, and tectonic discrimination diagrams are consistent with formation of these bodies in island arc settings. The highly calcic content of most of the plagioclase further supports an island arc origin for these bodies.

Khatyrka, a new CV3 find from the Koryak Mountains, Eastern Russia

AbstractA new meteorite find, named Khatyrka, was recovered from eastern Siberia as a result of a search for naturally occurring quasicrystals. The meteorite occurs as clastic grains within postglacial clay‐rich layers along the banks of a small stream in the Koryak Mountains, Chukotka Autonomous Okrug of far eastern Russia. Some of the grains are clearly chondritic and contain Type IA porphyritic olivine chondrules enclosed in matrices that have the characteristic platy olivine texture, matrix olivine composition, and mineralogy (olivine, pentlandite, nickel‐rich iron‐nickel metal, nepheline, and calcic pyroxene [diopside‐hedenbergite solid solution]) of oxidized‐subgroup CV3 chondrites. A few grains are fine‐grained spinel‐rich calcium‐aluminum‐rich inclusions with mineral oxygen isotopic compositions again typical of such objects in CV3 chondrites. The chondritic and CAI grains contain small fragments of metallic copper‐aluminum‐iron alloys that include the quasicrystalline phase icosahedrite. One grain is an achondritic intergrowth of Cu‐Al metal alloys and forsteritic olivine ± diopsidic pyroxene, both of which have meteoritic (CV3‐like) oxygen isotopic compositions. Finally, some grains consist almost entirely of metallic alloys of aluminum + copper ± iron. The Cu‐Al‐Fe metal alloys and the alloy‐bearing achondrite clast are interpreted to be an accretionary component of what otherwise is a fairly normal CV3 (oxidized) chondrite. This association of CV3 chondritic grains with metallic copper‐aluminum alloys makes Khatyrka a unique meteorite, perhaps best described as a complex CV3 (ox) breccia.

Constraints on the history of open‐basin lakes on Mars from the composition and timing of volcanic resurfacing

Abundant evidence exists for valley network‐related fluvial activity near the Noachian‐Hesperian transition on Mars, and areally significant quantities of volcanic ridged plains were emplaced during this period as well. Thus, it is worthwhile to explore the hypothesis that lava‐water interaction occurred on the surface of Mars at this time. We analyzed the morphology, physical properties, composition, and surface ages of thirty open‐basin lakes (topographic lows with both an inlet valley and an outlet valley) that were also resurfaced by volcanic flows. Hyperspectral imaging data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) instruments indicate that of the 30 basins, 12 exhibit the spectral properties of basaltic lithologies with diagnostic absorptions of olivine, high‐calcium pyroxene and low‐calcium pyroxene. An olivine/high‐calcium pyroxene mixture is the most commonly identified mineral assemblage, consistent with other Hesperian‐aged volcanic units. Therefore, our mineralogical results for over a third of the open‐basin lake floors analyzed support prior interpretations that the basins were resurfaced by volcanic flows. Supporting evidence for resurfacing by volcanic flows is also given by the observed morphology and physical properties (e.g., surface roughness, thermal inertia) of the resurfaced open‐basin lake floors. In these 30 examples, however, no evidence was found for lava‐water interaction. The ages of emplacement, derived through counts of superposed craters, of all 30 of the open‐basin lake volcanic resurfacing units show that resurfacing began in the Late Noachian, near the Noachian‐Hesperian boundary, was concentrated in the Hesperian, and continued into the Early Amazonian. The lack of geologic features indicative of lava‐water interaction suggests that the basins were likely to have been mostly devoid of water at the time of the latest phase of volcanic resurfacing. We conclude that there is no geologic evidence that suggests the fluvial activity associated with the studied paleolakes was coeval with the emplacement of the observed volcanic resurfacing units, several of which date to the Late Noachian‐Early Hesperian.

Composition and structures of the subsurface in the vicinity of Valles Marineris as revealed by central uplifts of impact craters

Despite recent efforts from space exploration to sound the martian subsurface with RADAR, the structure of the martian subsurface is still unknown. Major geologic contacts or discontinuities inside the martian crust have not been revealed. Another way to analyze the subsurface is to study rocks that have been exhumed from depth by impact processes. The last martian mission, MRO (Mars Reconnaissance Orbiter), put forth a great deal of effort in targeting the central peaks of impact craters with both of its high resolution instruments: CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) and HiRISE (High Resolution Science Experiment). We analyzed the composition with CRISM and the physical characteristics on HiRISE of the rocks exhumed from depth from 31 impact craters in the vicinity of Valles Marineris. Our analyses revealed the presence at depth of two kinds of material: massive light-toned rocks and intact layers. Exhumed light-toned massive rocks are enriched in low calcium pyroxenes and olivine. Hydrated phases such as smectites and putative serpentine are present and may provide evidence of hydrothermal processes. Some of the rocks may represent portions of the volatile-rich, pre-Noachian martian primitive crust. In the second class of central peaks, exhumed layers are deformed, folded, and fractured. Visible-near infrared (VNIR) spectra suggest that they are composed of a mixture of olivine and high calcium pyroxene associated with hydrated phases. These layers may represent a Noachian volcanic accumulation of up to 18km due to Tharsis activity. The spatial distribution, as well as the in-depth distribution between the two groups of rocks exhumed, are not random and reveal a major geologic discontinuity below the Tharsis lava plateau. The contact may be vertical over several kilometers depth suggesting the pre-existence of a steep basin (early giant impact or subsidence basin) or sagduction processes.

NIR spectral trends of HED meteorites: Can we discriminate between the magmatic evolution, mechanical mixing and observation geometry effects?

The Howardite–Eucrite–Diogenite (HED) suite is a family of differentiated meteorites that provide a unique opportunity to study the differentiation of small bodies. The likely parent-body of this meteorite group, (4) Vesta is presently under study by the Dawn mission, scrutinizing its surface in the visible and NIR infrared range. Here, we discuss how well the magmatic trends observed in HED might be retrieved from NIR spectroscopy, by studying laboratory spectra of 10 HED meteorites together with spectra from the RELAB database. We show that although an exsolution process did occur for most eucrites (i.e. decomposition of a primary calcic pyroxene into a high-Ca and low-Ca pyroxene), it does not affect the “bulk pyroxene” trend retrieved from the location of the pyroxene crystal field bands (Band I with a maximum of absorption around at about 1μm and Band II around 2μm). Absolute values of the chemical composition appears however to deviate from the expected chemical composition. We show that mechanical mixture (i.e. impact gardening) will produce a linear mixing in the pyroxenes band position diagram (Band I position vs Band II position). This diagram also reveals that howardite are not pure mixtures of an average eucrite and average diogenite. Because asteroid surfaces are expected to show topography, we also study the effect of observation geometry on the NIR spectra of an eucrite and a diogenite by measuring the bi-directional reflectance spectra from 0.4 to 4.6μm. Results show that these meteorites tend to act as forward scatterers, leading to a decrease of integrated band area (relative to the continuum) at high phase angles. The position of the two strong crystal field bands shows only small variability with observation geometry. Retrieval of the magmatic trends from the Band I vs Band II diagram should not be affected by observation geometry effects. Finally we performed NIR reflectance measurement on olivine diogenites. The presence of olivine can be suggested by using the Band Area Ratio vs Band I diagram, but this phase might affect the retrieval of pyroxene composition from the position of Band I and Band II.

Reflectance spectra of analog anorthosites: Implications for lunar highland mapping

Lunar highland region and associated craters are mostly composed of anorthosite. In the present study, we studied the reflectance spectra of terrestrial anorthosites collected from Sittampundi Anorthosites Complex, which is considered as equivalent (simulant) of lunar highland anorthosites. The objective of the study is to interpret diagnostic spectral features of analog anorthosite for remotely exploring lunar highland region. Reflectance spectra of anorthosites were measured under two different environments, such as controlled field and laboratory conditions. In these two procedures, the laboratory spectra give clear, diagnostic spectral information in the present study. Reflectance spectra captured under 350–2500 nm covering UV, Visible, NIR, and SWIR part of the electromagnetic spectrum. The spectral characteristics of anorthosites measured under various parts of electromagnetic spectrum have diagnostic absorption features at 380–387, 700–740, 930–1100, 1160–1200, 1415, 1920, 2200 and 2330 nm correspondingly due to plagioclase UV absorption, Fe 3+ electron transition absorption, Fe 2+ pyroxene and olivine absorption, OH/Mn 3+ crystal transition absorption, pyroxene absorption, Al–OH absorption and Mg–OH absorption. Mineralogical and chemical analyses were carried out for four anorthosites and compared with the results of chemical component of lunar anorthosite. The percentage of plagioclase content, relative abundance of low and high calcium pyroxene and olivine in different anorthosite samples are correlated with the albedo range, absorption shape, absorption centers and band depth. The similarity in the diagnostic spectral features of the anolog anorthosite with lunar anorthosites could be effectively utilized for remotely mapping the lunar highland region.

Mineralogy of recent volcanic plains in the Tharsis region, Mars, and implications for platy-ridged flow composition

Volcanism on Mars occurred until recently, but the mineralogy of recent lava plains is poorly known because few regions display fresh outcrops devoid of dust. Using visible and near infrared data of the Mars Express probe, two new volcanic plains in Noctis Labyrinthus have been identified, and the existence of a volcanic plain on the floor of Echus Chasma has been confirmed. Crater retention ages estimated for these three plains range between 50 and 100 My, corresponding to the Late Amazonian. These plains represent an excellent opportunity to constrain the mineralogy of recent volcanic rocks. Results show that basaltic compositions with plagioclase and high calcium pyroxene are predominant. The low olivine proportion suggests that the apparent fluidity of these flat plains is not related to magmas being ultramafic. In addition, a platy-ridged texture is observed in two of the studied regions. Our study shows, for the first time, that this texture is associated with volcanic rocks, and that these rocks are of typical basaltic mineralogy. Finally, these volcanic plains are located more than 1000 km east of previously known Late Amazonian volcanic centers of the Tharsis region, an observation to be taken into account when considering models of recent volcanism on Mars.