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C M Pieters - One of the best experts on this subject based on the ideXlab platform.
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complexities in Pyroxene compositions derived from absorption band centers examples from apollo samples hed meteorites synthetic pure Pyroxenes and remote sensing data
Meteoritics & Planetary Science, 2016Co-Authors: D P Moriarty, C M PietersAbstract:We reexamine the relationship between Pyroxene composition and near-infrared absorption bands, integrating measurements of diverse natural and synthetic samples. We test an algorithm (PLC) involving a two-part linear continuum removal and parabolic fits to the 1 and 2 μm bands—a computationally simple approach which can easily be automated and applied to remote sensing data. Employing a suite of synthetic pure Pyroxenes, the PLC technique is shown to derive similar band centers to the modified Gaussian model. PLC analyses are extended to natural Pyroxene-bearing materials, including (1) bulk lunar basalts and Pyroxene separates, (2) diverse lunar soils, and (3) HED meteorites. For natural Pyroxenes, the relationship between composition and absorption band center differs from that of synthetic Pyroxenes. These differences arise from complexities inherent in natural materials such as exsolution, zoning, mixing, and space weathering. For these reasons, band center measurements of natural Pyroxene-bearing materials are compositionally nonunique and could represent three distinct scenarios (1) Pyroxene with a narrow compositional range, (2) complexly zoned Pyroxene grains, or (3) a mixture of multiple Pyroxene (or nonPyroxene) components. Therefore, a universal quantitative relationship between band centers and Pyroxene composition cannot be uniquely derived for natural Pyroxene-bearing materials without additional geologic context. Nevertheless, useful relative relationships between composition and band center persist in most cases. These relationships are used to interpret M3 data from the Humboldtianum Basin. Four distinct compositional units are identified (1) Mare Humboldtianum basalts, (2) distinct outer basalts, (3) low-Ca Pyroxene-bearing materials, and (4) feldspathic materials.
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new insights into lunar petrology distribution and composition of prominent low ca Pyroxene exposures as observed by the moon mineralogy mapper m3
Journal of Geophysical Research, 2011Co-Authors: R L Klima, C M Pieters, J Boardman, Robert O Green, James W Head, P Isaacson, John F Mustard, Jeff Nettles, N E Petro, M StaidAbstract:[1] Lunar geochemical groups such as Mg suite, ferroan anorthosite, and alkali suite rocks are difficult to distinguish from orbit because they are defined by both modal mineralogy and elemental composition of their constituent minerals. While modal mineralogy can be modeled, only specific minerals or elements can be directly detected. At near-infrared (NIR) wavelengths, Pyroxenes are among the most spectrally distinctive minerals, and their absorption bands are sensitive to structure and composition. Pyroxenes thus provide important clues to distinguish these geochemical groups and to understand lunar crustal evolution. Using Moon Mineralogy Mapper data, we search for lithologies dominated by strong low-calcium Pyroxene (LCP) signatures. We compare the NIR absorptions of 20 LCPs to a suite of synthetic Pyroxenes to determine which lunar Pyroxenes appear magnesian enough to be candidate Mg suite norites. We detail three prominent regions of LCP (1) in South Pole–Aitken Basin (SPA), (2) south of Mare Frigoris, and (3) north of Mare Frigoris. The absorption band positions suggest that the LCPs north of Mare Frigoris and those in SPA are compositionally similar to one another and of ∼Mg50–75, implying that the mafic material excavated by the SPA impact was relatively iron-rich. Modified Gaussian modeling results suggest that the Apollo basin may have tapped different composition material than is exposed in much of SPA. The LCPs located in the highlands south of Mare Frigoris exhibit absorption bands at short wavelengths consistent with Mg > ∼80. The coincidence of these Mg-rich LCPs with the thorium measured by Lunar Prospector make them good candidates for KREEP-related Mg suite Pyroxenes.
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near infrared spectra of clinoPyroxenes effects of calcium content and crystal structure
Meteoritics & Planetary Science, 2011Co-Authors: R L Klima, Darby M Dyar, C M PietersAbstract:Pyroxenes are among the most common minerals in the solar system and are ideally suited for remote geochemical analysis because of the sensitivity of their distinctive spectra to mineral composition. Fe 2+ is responsible for the dominant Pyroxene absorptions in the visible and near-infrared, but substitutions of other cations such as Ca 2+ change the crystal structure and site geometries and thus the crystal field splitting energies of the Fe cations. To define spectral systematics resulting from major Pyroxene cations (Ca 2+ ,M g 2+ , and Fe 2+ ), we focus on a suite of Pyroxenes synthesized with only Ca 2+ ,M g 2+ , and Fe 2+ in the two octahedral sites, specifically examining the effect of Ca 2+ on Pyroxene absorption bands. The modified Gaussian model is used to deconvolve Pyroxene spectra into component bands that can then be linked directly to crystal field absorptions. In orthoPyroxenes and low-Ca clinoPyroxenes, Ca 2+ -content has a strong and predictable effect on the positions of the absorption bands. At a threshold of Wo30, the crystal field environment stagnates and the M2 bands cease to change significantly as more Ca 2+ is added. At Wo50, when most of the M2 sites are filled by Ca 2+ , band positions do not change drastically, although the presence and strengths of the 1 and 2 lm bands are affected by even trace amounts of Fe 2+ in the M2 site. It is thus apparent that next-nearest neighbors and the distortions they impose on the Pyroxene lattice affect the electronic states around the Fe 2+ cations and control absorption band properties.
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characterization of the 1 2 μm m1 Pyroxene band extracting cooling history from near ir spectra of Pyroxenes and Pyroxene dominated rocks
Meteoritics & Planetary Science, 2008Co-Authors: R L Klima, C M Pieters, Darby M DyarAbstract:The 1.2 m band in near-infrared spectra of Pyroxenes results from Fe2+ in the M1 crystallographic site. The distribution of Fe and Mg between the M1 and M2 sites is in part a function of the cooling rate and thermal history of a Pyroxene. Combining near-infrared and Mssbauer spectra for a series of compositionally controlled synthetic Mg, Fe, Ca Pyroxenes, we quantify the strength of the 1.2 m band as a function of Fe2+ in the M1 site. Near-infrared spectra are deconvolved into component absorptions that can be assigned to the M1 and M2 sites using the modified Gaussian model. The relative strength of the 1.2 μm band is shown to be directly related to the amount of Fe2+ in the M1 site measured by Mossbauer spectroscopy. The strength of the 1.2 μm band relative to the combined strengths of the 1.2 and 2 μm bands, or the M1 intensity ratio, is calculated for 51 howardite, eucrite, and diogenite (HED) meteorites. Diogenites and cumulate eucrites exhibit the lowest M1 intensity ratios, consistent with their formation as slowly cooled cumulates. Basaltic eucrites exhibit a large range of M1 intensity ratios, all of which are consistently higher than the diogenites and cumulate eucrites. This example illustrates how the M1 intensity ratio can be a used as a tool for characterizing the cooling history of remotely detected Pyroxene-dominated rocks.
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estimating modal abundances from the spectra of natural and laboratory Pyroxene mixtures using the modified gaussian model
Journal of Geophysical Research, 1993Co-Authors: J M Sunshine, C M PietersAbstract:Spectra of samples containing multiple Pyroxene components are explored as a function of modal abundance using the modified Gaussian model (MGM). The MGM, unlike other approaches, allows spectra to be analyzed directly, without the use of actual or assumed end-member spectra and therefore holds great potential for remote applications. Quantitative understanding of the spectral characteristics of lithologies which include mixtures of two or more Pyroxenes is fundamental to analyzing remotely acquired spectra of terrestrial and extra-terrestrial targets. A series of mass fraction mixtures created from several different particle size fractions were analyzed with the MGM to quantify the properties of Pyroxene mixtures as a function of both modal abundance and grain size. Results of this MGM analysis indicate that band centers, band widths, and relative band strengths of absorptions from individual Pyroxenes in mixture spectra are largely independent of particle size. In addition, systematic changes in relative band strength as a function of modal abundance are observed, which yield particle size independent relationships that can be used to estimate modal abundances from the spectra of unknown samples. Spectra of natural samples exhibiting both zoned and exsolved Pyroxenes are evaluated as examples of spectra likely to be measured from actual lithologies. Spectral properties of both Pyroxene components are resolved in exsolved samples using the MGM, and modal abundances are accurately estimated to within 5-10% without predetermined knowledge of the end-member spectra. In contrast, the spectra of samples exhibiting zoned compositions are consistent with one dominant Pyroxene component. This single Pyroxene component has anomalously wide absorption bands and appears to represent an average composition.
Yan Liang - One of the best experts on this subject based on the ideXlab platform.
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a ree in two Pyroxene thermometer for mafic and ultramafic rocks
Geochimica et Cosmochimica Acta, 2013Co-Authors: Yan LiangAbstract:Abstract A REE-in-two-Pyroxene thermometer for mafic and ultramafic rocks has been developed on the basis of the temperature and Pyroxene composition dependent rare earth element (REE) partitioning between coexisting orthoPyroxene and clinoPyroxene. This trace element based two-Pyroxene thermometer is built on two parameterized lattice strain models for REE partitioning between Pyroxene and basaltic melt that were independently calibrated using data from Pyroxene-melt partitioning experiments ( Sun and Liang, 2012 , Yao et al., 2012 ). By treating REE and Y as a group in temperature calculations, one can reduce analytical uncertainties in trace element analysis through least squares inversion of orthoPyroxene–clinoPyroxene partitioning data, and identify and exclude variations induced by secondary or metasomatic processes. For convenience, a simple robust regression program is provided for temperature inversion. Application of the REE-in-two-Pyroxene thermometer to well-equilibrated spinel lherzolite and harzburgite xenoliths from the continental lithosphere demonstrates the internal consistency of the two Pyroxene-melt REE partitioning models and the trace and major element based Pyroxene thermometers: temperatures derived from the REE-in-two-Pyroxene thermometer agree very well with temperatures calculated using major element based Pyroxene thermometers. Applications of the REE-in-two-Pyroxene thermometer to abyssal peridotites and mafic cumulates reveal a significant difference in the calculated temperatures between the REE and major element based Pyroxene thermometers: temperatures derived from the REE-in-two-Pyroxene thermometer are consistently higher than those derived from the major element based Pyroxene thermometers. This discrepancy in temperature likely results from a difference in diffusion rate and hence closure temperature between the 2+ and 3+ cations in the Pyroxenes. An independently calibrated REE-in-two-Pyroxene thermometer may offer new insight into the thermal history of mafic and ultramafic rocks from the upper mantle and lower crust.
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ti diffusion in natural Pyroxene
Geochimica et Cosmochimica Acta, 2012Co-Authors: D J Cherniak, Yan LiangAbstract:Abstract Diffusion of Ti has been characterized in natural orthoPyroxene and clinoPyroxene under buffered conditions (IW, NNO, and QFM) and in air. In all Pyroxene compositions studied, titanium diffusion appears relatively insensitive to crystallographic orientation and oxygen fugacity under the range of investigated conditions. For Ti diffusion in a natural enstatite and a Kilbourne Hole orthoPyroxene (KBH opx), we obtain the following Arrhenius relations for diffusion over the temperature range 950–1150 °C, D En = 1.45 × 10 - 11 exp ( - 270 ± 34 kJ mol - 1 / RT ) m 2 s - 1 , D KBH = 3.70 × 10 - 11 exp ( - 285 ± 34 kJ mol - 1 / RT ) m 2 s - 1 . For Ti diffusion in a natural diopside and a chromian diopside at temperatures 900–1250 °C we obtain the following Arrhenius relations, respectively, D Di = 8.01 × 10 - 11 exp ( - 282 ± 20 kJ mol - 1 / RT ) m 2 s - 1 , D CrDi = 2.97 × 10 - 11 exp ( - 282 ± 40 kJ mol - 1 / RT ) m 2 s - 1 . Diffusion rates of Ti in the Cr-diopside and KBH opx are essentially the same, whereas diffusion rates of Ti in the enstatite and diopside are only 1.3–1.8 times and 2.7–2.9 times that in the KBH opx, respectively. Titanium diffusion appears relatively insensitive to Pyroxene composition, in contrast to findings for diffusion of some other cations. At magmatic temperatures, the rates of Ti diffusion in Pyroxene are comparable to the rates of REE diffusion in opx and the rates of Al and MREE diffusion in diopside, although activation energies of Ti diffusion are considerably lower than those for REE diffusion in the Pyroxenes. Finally, diffusion rates of Ti in Pyroxenes are 1–3 orders of magnitude smaller than those of Mg and Fe in Pyroxenes. Diffusivities of Ti in Pyroxenes obtained from this study can be used to understand a range of geochemical mass transfer problems involving diopside and orthoPyroxene. The closure temperatures for Ti in orthoPyroxene and diopside are very similar to each other for comparable Pyroxene grain size. Subsolidus redistribution of Ti between orthoPyroxene and diopside results in characteristic reverse Ti zoning in orthoPyroxene and normal Ti zoning in diopside. Such zoning patterns in coexisting orthoPyroxene and diopside may be used to infer cooling rate of two-Pyroxene bearing ultramafic and mafic rocks.
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a parameterized model for ree distribution between low ca Pyroxene and basaltic melts with applications to ree partitioning in low ca Pyroxene along a mantle adiabat and during pyroxenite derived melt and peridotite interaction
Contributions to Mineralogy and Petrology, 2012Co-Authors: Yan LiangAbstract:Low-Ca Pyroxenes play an important role in mantle melting, melt-rock reaction, and magma differentiation processes. In order to better understand REE fractionation during adiabatic mantle melting and pyroxenite-derived melt and peridotite interaction, we developed a parameterized model for REE partitioning between low-Ca Pyroxene and basaltic melts. Our parameterization is based on the lattice strain model and a compilation of published experimental data, supplemented by a new set of trace element partitioning experiments for low-Ca Pyroxenes produced by pyroxenite-derived melt and peridotite interaction. To test the validity of the assumptions and simplifications used in the model development, we compared model-derived partition coefficients with measured partition coefficients for REE between orthoPyroxene and clinoPyroxene in well-equilibrated peridotite xenoliths. REE partition coefficients in low-Ca Pyroxene correlate negatively with temperature and positively with both calcium content on the M2 site and aluminum content on the tetrahedral site of Pyroxene. The strong competing effect between temperature and major element compositions of low-Ca Pyroxene results in very small variations in REE partition coefficients in orthoPyroxene during adiabatic mantle melting when diopside is in the residue. REE partition coefficients in orthoPyroxene can be treated as constants at a given mantle potential temperature during decompression melting of lherzolite and diopside-bearing harzburgite. In the absence of diopside, partition coefficients of light REE in orthoPyroxene vary significantly, and such variations should be taken into consideration in geochemical modeling of REE fractionation in clinoPyroxene-free harzburgite. Application of the parameterized model to low-Ca Pyroxenes produced by reaction between pyroxenite-derived melt and peridotite revealed large variations in the calculated REE partition coefficients in the low-Ca Pyroxenes. Temperature and composition of starting pyroxenite must be considered when selecting REE partition coefficients for pyroxenite-derived melt and peridotite interaction.
Yasuyuki Banno - One of the best experts on this subject based on the ideXlab platform.
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paragenesis of sodic Pyroxene bearing quartz schists implications for the p t history of the sanbagawa belt
Contributions to Mineralogy and Petrology, 1994Co-Authors: Masaki Enami, Simon Wallis, Yasuyuki BannoAbstract:Sodic Pyroxene (jadeite content X jd=0.1–0.3) occurs locally as small inclusions within, albite porphyroblasts and in the matrix of hematite-bearing quartz schists in the Sanbagawa (Sambagawa) metamorphic belt, central Shikoku, Japan. The sodic, Pyroxene-bearing samples are characteristically free from chlorite and their typical mineral assemblage is sodic Pyroxene+subcalcic (or sodic) amphibole+phengitic mica+albite+quartz+hematite+titanite±epidote. Spessartine-rich garnet occurs in Mn-rich samples. Sodic Pyroxene in epidote-bearing samples tends to be poorer in acmite content (average X Acm=0.26–0.50) than that in the epidote-free samples (X Acm=0.45–0.47). X Jd shows no systematic relationship to metamorphic grade, and is different among the three sampling regions [Saruta-gawa, Asemi-gawa and Bessi (Besshi)]. The average X Jd of the Saruta-gawa samples (0.21–0.29) is higher than that of the Asemi-gawa (0.13–0.17) and Bessi (0.14–0.23). The P-T conditions of the Asemi-gawa and Bessi regions are estimated at 5.5–6.5 kbar, >360°C in the chlorite zone, 7–8.5 kbar, 440±15°C in the garnet zone and 8–9.5 kbar, 520±25°C in the albite-biotite zone. Metamorphic pressure of the Saruta-gawa region is systematically 1–1.5 kbar higher than that of the Asemi-gawa and Bessi regions, and materials of the Saruta-gawa region have been subducted to a level 3–5 km deeper than materials that underwent metamorphism at equivalent temperatures and are now exposed in the Asemi-gawa and Bessi regions. Pressure slightly increases toward the north (structurally high levels) through the Sanbagawa belt of central shikoku. Two types of zonal structure were observed in relatively coarse-grained sodic Pyroxenes in the matrix. One type is characterized by increasing X Jd from core to rim, the other type by decreasing X Jd from core to rim. Both types of zoned Pyroxenes show an increase in X Fe 2+[=Fe2+/(Fe2++Mg)] from core to rim. The first type of zoning was observed in a sample from the chlorite zone of lowest grade, whereas the latter occurs in the garnet and albite-biotite zones of higher grade. The contrast in zonal structure implies that dP/dT during prograde metamorphism decreased with increasing metamorphic grade and may have been negative in some samples from the higher-grade zones. The estimated dP/dT of the prograde stage of the chlorite zone is 3.2 kbar/100°C, and that of the garnet and albite-biotite zones is -1.8 to 0.9 kbar/100°C. The variation of dP/dT at shallow and deep levels of a subduction system probably reflects the difference of heating duration and/or change in thermal gradient of the subduction zone by continuous cooling of the surrounding mantle.
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chromian sodic Pyroxene phengite and allanite from the sanbagawa blueschists in the eastern kii peninsula central japan
Mineralogical Journal, 1993Co-Authors: Yasuyuki BannoAbstract:Chromian aegirine – aegirine-augite, phengite and allanite occur in blueschists, which are interbedded with serpentinite conglomerates, in the Ise area of the Sanbagawa belt, central Japan. Aggregates of chromian phengite±sodic Pyroxene are scattered in the blueschists, and often include detrital chromian spinel. Sodic Pyroxene in the aggregate shows solid solution between aegirine and kosmochlor components with a maximum 12.8 wt.% Cr2O3 (kosmochlor component = 38 mol%). Sodic Pyroxene also occurs as individual crystal in the matrix, and has lower Cr2O3 (up to 0.7 wt.%). Phengite has a maximum 17.8 wt.% Cr2O3 showing a substitution of Cr for Al in octahedral sites. Allanite occurs in an aggregate of chromian phengite, sodic Pyroxene and detrital chromian spinel, and contains up to 7.5 wt.% Cr2O3. Chromium in sodic Pyroxene, phengite and allanite is derived from detrital chromian spinel. Distinct difference in Cr2O3 content between sodic Pyroxenes in the aggregate and matrix suggests limited diffusion of Cr during the recrystallization.
Guy Libourel - One of the best experts on this subject based on the ideXlab platform.
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an experimental study of Pyroxene crystallization during rapid cooling in a thermal gradient application to komatiites
Solid Earth, 2014Co-Authors: S Bouquain, Nicholas T Arndt, Francois Faure, Guy LibourelAbstract:To investigate the crystallization of Pyroxene in spinifex-textured komatiites, we undertook a series of experiments in which compositions in the CaO-MgO-Al 2 O 3 -SiO 2 CMAS system were cooled rapidly in a thermal gradient. Cooling rates were generally between 5 and 10 °C h −1 , but some runs were made at 100–200 °C h −1 ; thermal gradients were between 10 and 20 °C cm −1 . These conditions reproduced those at various depths in the crust of komatiite lava flow. The starting composition was chosen to have pigeonite on the liquidus, and most of the experimental charges crystallized zoned pigeonite–diopside crystals like those in komatiite lavas. An intriguing aspect of the experimental results was their lack of reproducibility. Some experiments crystallized forsterite, whereas others that were run under similar conditions crystallized two Pyroxenes and no forsterite; some experiments were totally glassy, but others crystallized entirely to Pyroxene. The degree of supercooling at the onset of Pyroxene crystallization was variable, from less than 25 °C to more than 110 °C. We attribute these results to the difficulty of nucleation of Pyroxene under the conditions of the experiments. In some cases forsterite crystallized metastably and modified the liquid composition to inhibit Pyroxene crystallization; in others no nucleation took place until a large degree of supercooling was achieved, and then Pyroxene crystallized rapidly. Pigeonite crystallized under a wide range of conditions, at cooling rates from 3 to 100 °C h −1 . The notion that this mineral only forms at low cooling rates is not correct.
R L Klima - One of the best experts on this subject based on the ideXlab platform.
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new insights into lunar petrology distribution and composition of prominent low ca Pyroxene exposures as observed by the moon mineralogy mapper m3
Journal of Geophysical Research, 2011Co-Authors: R L Klima, C M Pieters, J Boardman, Robert O Green, James W Head, P Isaacson, John F Mustard, Jeff Nettles, N E Petro, M StaidAbstract:[1] Lunar geochemical groups such as Mg suite, ferroan anorthosite, and alkali suite rocks are difficult to distinguish from orbit because they are defined by both modal mineralogy and elemental composition of their constituent minerals. While modal mineralogy can be modeled, only specific minerals or elements can be directly detected. At near-infrared (NIR) wavelengths, Pyroxenes are among the most spectrally distinctive minerals, and their absorption bands are sensitive to structure and composition. Pyroxenes thus provide important clues to distinguish these geochemical groups and to understand lunar crustal evolution. Using Moon Mineralogy Mapper data, we search for lithologies dominated by strong low-calcium Pyroxene (LCP) signatures. We compare the NIR absorptions of 20 LCPs to a suite of synthetic Pyroxenes to determine which lunar Pyroxenes appear magnesian enough to be candidate Mg suite norites. We detail three prominent regions of LCP (1) in South Pole–Aitken Basin (SPA), (2) south of Mare Frigoris, and (3) north of Mare Frigoris. The absorption band positions suggest that the LCPs north of Mare Frigoris and those in SPA are compositionally similar to one another and of ∼Mg50–75, implying that the mafic material excavated by the SPA impact was relatively iron-rich. Modified Gaussian modeling results suggest that the Apollo basin may have tapped different composition material than is exposed in much of SPA. The LCPs located in the highlands south of Mare Frigoris exhibit absorption bands at short wavelengths consistent with Mg > ∼80. The coincidence of these Mg-rich LCPs with the thorium measured by Lunar Prospector make them good candidates for KREEP-related Mg suite Pyroxenes.
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near infrared spectra of clinoPyroxenes effects of calcium content and crystal structure
Meteoritics & Planetary Science, 2011Co-Authors: R L Klima, Darby M Dyar, C M PietersAbstract:Pyroxenes are among the most common minerals in the solar system and are ideally suited for remote geochemical analysis because of the sensitivity of their distinctive spectra to mineral composition. Fe 2+ is responsible for the dominant Pyroxene absorptions in the visible and near-infrared, but substitutions of other cations such as Ca 2+ change the crystal structure and site geometries and thus the crystal field splitting energies of the Fe cations. To define spectral systematics resulting from major Pyroxene cations (Ca 2+ ,M g 2+ , and Fe 2+ ), we focus on a suite of Pyroxenes synthesized with only Ca 2+ ,M g 2+ , and Fe 2+ in the two octahedral sites, specifically examining the effect of Ca 2+ on Pyroxene absorption bands. The modified Gaussian model is used to deconvolve Pyroxene spectra into component bands that can then be linked directly to crystal field absorptions. In orthoPyroxenes and low-Ca clinoPyroxenes, Ca 2+ -content has a strong and predictable effect on the positions of the absorption bands. At a threshold of Wo30, the crystal field environment stagnates and the M2 bands cease to change significantly as more Ca 2+ is added. At Wo50, when most of the M2 sites are filled by Ca 2+ , band positions do not change drastically, although the presence and strengths of the 1 and 2 lm bands are affected by even trace amounts of Fe 2+ in the M2 site. It is thus apparent that next-nearest neighbors and the distortions they impose on the Pyroxene lattice affect the electronic states around the Fe 2+ cations and control absorption band properties.
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characterization of the 1 2 μm m1 Pyroxene band extracting cooling history from near ir spectra of Pyroxenes and Pyroxene dominated rocks
Meteoritics & Planetary Science, 2008Co-Authors: R L Klima, C M Pieters, Darby M DyarAbstract:The 1.2 m band in near-infrared spectra of Pyroxenes results from Fe2+ in the M1 crystallographic site. The distribution of Fe and Mg between the M1 and M2 sites is in part a function of the cooling rate and thermal history of a Pyroxene. Combining near-infrared and Mssbauer spectra for a series of compositionally controlled synthetic Mg, Fe, Ca Pyroxenes, we quantify the strength of the 1.2 m band as a function of Fe2+ in the M1 site. Near-infrared spectra are deconvolved into component absorptions that can be assigned to the M1 and M2 sites using the modified Gaussian model. The relative strength of the 1.2 μm band is shown to be directly related to the amount of Fe2+ in the M1 site measured by Mossbauer spectroscopy. The strength of the 1.2 μm band relative to the combined strengths of the 1.2 and 2 μm bands, or the M1 intensity ratio, is calculated for 51 howardite, eucrite, and diogenite (HED) meteorites. Diogenites and cumulate eucrites exhibit the lowest M1 intensity ratios, consistent with their formation as slowly cooled cumulates. Basaltic eucrites exhibit a large range of M1 intensity ratios, all of which are consistently higher than the diogenites and cumulate eucrites. This example illustrates how the M1 intensity ratio can be a used as a tool for characterizing the cooling history of remotely detected Pyroxene-dominated rocks.
