The Experts below are selected from a list of 738 Experts worldwide ranked by ideXlab platform
Carl B. Agee - One of the best experts on this subject based on the ideXlab platform.
-
The chlorine isotopic composition of Martian meteorites 1: Chlorine isotope composition of Martian mantle and crustal reservoirs and their interactions
Meteoritics & Planetary Science, 2016Co-Authors: J. T. Williams, Francis M. Mccubbin, Charles K. Shearer, Carl B. Agee, Zachary D. Sharp, Paul V. Burger, A. R. Santos, Kevin D. MckeeganAbstract:The Martian meteorites record a wide diversity of environments, processes, and ages. Much work has been done to decipher potential mantle sources for Martian magmas and their interactions with crustal and surface environments. Chlorine isotopes provide a unique opportunity to assess interactions between Martian mantle-derived magmas and the crust. We have measured the Cl-isotopic composition of 17 samples that span the range of known ages, Martian environments, and mantle reservoirs. The 37Cl of the Martian mantle, as represented by the olivine-phyric shergottites, NWA 2737 (chassignite), and Shergotty (basaltic shergottite), has a low value of approximately −3.8‰. This value is lower than that of all other planetary bodies measured thus far. The Martian crust, as represented by regolith breccia NWA 7034, is variably enriched in the heavy isotope of Cl. This enrichment is reflective of preferential loss of 35Cl to space. Most basaltic shergottites (less Shergotty), Nakhlites, Chassigny, and Allan Hills 84001 lie on a continuum between the Martian mantle and crust. This intermediate range is explained by mechanical mixing through impact, fluid interaction, and assimilation-fractional crystallization.
-
lithium isotope constraints on crust mantle interactions and surface processes on mars
Geochimica et Cosmochimica Acta, 2015Co-Authors: Tomas Magna, James M.d. Day, Klaus Mezger, Manuela A Fehr, Ralf Dohmen, Hasnaa Chennaoui Aoudjehane, Carl B. AgeeAbstract:Abstract Lithium abundances and isotope compositions are reported for a suite of martian meteorites that span the range of petrological and geochemical types recognized to date for Mars. Samples include twenty-one bulk-rock enriched, intermediate and depleted shergottites, six Nakhlites, two chassignites, the orthopyroxenite Allan Hills (ALH) 84001 and the polymict breccia Northwest Africa (NWA) 7034. Shergottites unaffected by terrestrial weathering exhibit a range in δ7Li from 2.1 to 6.2‰, similar to that reported for pristine terrestrial peridotites and unaltered mid-ocean ridge and ocean island basalts. Two chassignites have δ7Li values (4.0‰) intermediate to the shergottite range, and combined, these meteorites provide the most robust current constraints on δ7Li of the martian mantle. The polymict breccia NWA 7034 has the lowest δ7Li (−0.2‰) of all terrestrially unaltered martian meteorites measured to date and may represent an isotopically light surface end-member. The new data for NWA 7034 imply that martian crustal surface materials had both a lighter Li isotope composition and elevated Li abundance compared with their associated mantle. These findings are supported by Li data for olivine-phyric shergotitte NWA 1068, a black glass phase isolated from the Tissint meteorite fall, and some Nakhlites, which all show evidence for assimilation of a low-δ7Li crustal component. The range in δ7Li for Nakhlites (1.8 to 5.2‰), and co-variations with chlorine abundance, suggests crustal contamination by Cl-rich brines. The differences in Li isotope composition and abundance between the martian mantle and estimated crust are not as large as the fractionations observed for terrestrial continental crust and mantle, suggesting a difference in the styles of alteration and weathering between water-dominated processes on Earth versus possibly Cl–S-rich brines on Mars. Using high-MgO shergottites (>15 wt.% MgO) it is possible to estimate the δ7Li of Bulk Silicate Mars (BSM) to be 4.2 ± 0.9‰ (2σ). This value is at the higher end of estimates for the Bulk Silicate Earth (BSE; 3.5 ± 1.0‰, 2σ), but overlaps within uncertainty.
-
Evidence for a widespread basaltic breccia component in the martian low-albedo regions from the reflectance spectrum of Northwest Africa 7034
Icarus, 2015Co-Authors: Kevin M. Cannon, John F. Mustard, Carl B. AgeeAbstract:Northwest Africa (NWA) 7034 is the first breccia meteorite from Mars, and unlike the shergottite, nakhlite, and chassignite (SNC) martian meteorites, it matches the estimated chemical composition of martian crust. Here we show that the visible-infrared reflectance spectrum of NWA 7034 is unique compared to other SNCs and is more similar than them to remotely sensed data from Mars, suggesting the martian regolith may contain significant brecciated material produced during heavy bombardment of the crust.
-
Unique Meteorite from Early Amazonian Mars: Water-Rich Basaltic Breccia Northwest Africa 7034
Science (New York N.Y.), 2013Co-Authors: Carl B. Agee, Francis M. Mccubbin, R. Shaheen, Nicole V. Wilson, Karen Ziegler, Victor J. Polyak, Zachary D. Sharp, Yemane Asmerom, Morgan H. Nunn, Mark H. ThiemensAbstract:We report data on the martian meteorite Northwest Africa (NWA) 7034, which shares some petrologic and geochemical characteristics with known martian meteorites of the SNC (i.e., shergottite, nakhlite, and chassignite) group, but also has some unique characteristics that would exclude it from that group. NWA 7034 is a geochemically enriched crustal rock compositionally similar to basalts and average martian crust measured by recent Rover and Orbiter missions. It formed 2.089 ± 0.081 billion years ago, during the early Amazonian epoch in Mars9 geologic history. NWA 7034 has an order of magnitude more indigenous water than most SNC meteorites, with up to 6000 parts per million extraterrestrial H2O released during stepped heating. It also has bulk oxygen isotope values of Δ17O = 0.58 ± 0.05 per mil and a heat-released water oxygen isotope average value of Δ17O = 0.330 ± 0.011 per mil, suggesting the existence of multiple oxygen reservoirs on Mars.
T Mikouchi - One of the best experts on this subject based on the ideXlab platform.
-
oxidation state of Nakhlites as inferred from fe ti oxide equilibria and augite melt europium partitioning
Lunar and Planetary Science Conference, 2007Co-Authors: J Makishima, Gordon A Mckay, M Miyamoto, T MikouchiAbstract:Recent studies have shown that Martian magmas had wide range of oxygen fugacities (fO2) and that this variation is correlated with the variation of La/Yb ratio and isotopic characteristics of the Martian basalts, shergottite meteorites. The origin of this correlation must have important information about mantle sources and Martian evolution. In order to understand this correlation, it is necessary to know accurate value of oxidation state of other Martian meteorite groups. Nakhlites, cumulate clinopyroxenites, are another major group of Martian meteorites and have distinctly different trace element and isotopic characteristics from shergottites. Thus, estimates of oxidation state of Nakhlites will give us important insight into the mantle source in general. Several workers have estimated oxidation state of Nakhlites by using Fe-Ti oxide equilibrium. However, Fe-Ti oxides may not record the oxidation state of the parent melt of the nakhlite because it is a late-stage mineral. Furthermore, there is no comprehensive study which analyzed all nakhlite samples at the same time. Therefore, in this study (1) we reduced the uncertainty of the estimate using the same electron microprobe and the same standards under the same condition for Fe-Ti oxide in 6 Nakhlites and (2) we also performed crystallization experiments to measure partition coefficients of Eu into pyroxene in the nakhlite system in order to estimate fO2 when the pyroxene core formed (i.e. Eu oxybarometer [e.g. 2,6]).
-
mineralogy and petrology of the dar al gani 476 martian meteorite implications for its cooling history and relationship to other shergottites
Meteoritics & Planetary Science, 2001Co-Authors: T Mikouchi, Masamichi Miyamoto, G MckayAbstract:— Dar al Gani 476, the 13th martian meteorite, was recovered from the Sahara in 1998. It is a basaltic shergottitic rock composed of olivine megacrysts reaching 5 mm (24 vol%) set in a finegrained groundmass of pyroxene (59 vol%) and maskelynitized plagioclase (12 vol%) with minor amounts of accessory phases (spinel, merrillite, ilmenite). Dar al Gani 476 is similar to lithology A of Elephant Moraine A79001 (EETA79001) in petrography and mineralogy, but is distinct in several aspects. Low-Ca pyroxenes in the Dar al Gani 476 groundmass are more magnesian (En76Fs21 Wo3∼En58Fs30Wo12) than those in lithology A of EETA79001 (En73Fs22Wo5∼En45Fs43Wo12), rather similar to pyroxenes in lherzolitic martian meteorites (En76Fs21 Wo3∼En63Fs22Wo15). Dar al Gani 476 olivine is less magnesian and shows a narrower compositional range (Fo76-58) than EETA79001 olivine (Fo81-53), and is also similar to olivines in lherzolitic martian meteorites (Fo74-65). The orthopyroxene-olivine-chromite xenolith typical in the lithology A of EETA79001 is absent in Dar al Gani 476. It seems that Dar al Gani 476 crystallized from a slightly more primitive mafic magma than lithology A of EETA79001 and several phases (olivine, pyroxene, chromite, and ilmenite) in Dar al Gani 476 may have petrogenetic similarities to those of lherzolitic martian meteorites. Olivine megacrysts in Dar al Gani 476 are in disequilibrium with the bulk composition. The presence of fractured olivine grains in which the most Mg-rich parts are in contact with the groundmass suggests that little diffusive modification of original olivine compositions occurred during cooling. This observation enabled us to estimate the cooling rates of Dar al Gani 476 and EETA79001 olivines, giving similar cooling rates of 0.03-3 °C/h for Dar al Gani 476 and 0.05-5 °C/h for EETA79001. This suggests that they were cooled near the surface (burial depth shallower than about 3 m at most), probably in lava flows during crystallization of groundmass. As is proposed for lithology A of EETA79001, it may be possible to consider that Dar al Gani 476 has an impact melt origin, a mixture of martian lherzolite and other martian rock (Queen Alexandra Range 94201, Nakhlites?).
G Mckay - One of the best experts on this subject based on the ideXlab platform.
-
mineralogy and petrology of the dar al gani 476 martian meteorite implications for its cooling history and relationship to other shergottites
Meteoritics & Planetary Science, 2001Co-Authors: T Mikouchi, Masamichi Miyamoto, G MckayAbstract:— Dar al Gani 476, the 13th martian meteorite, was recovered from the Sahara in 1998. It is a basaltic shergottitic rock composed of olivine megacrysts reaching 5 mm (24 vol%) set in a finegrained groundmass of pyroxene (59 vol%) and maskelynitized plagioclase (12 vol%) with minor amounts of accessory phases (spinel, merrillite, ilmenite). Dar al Gani 476 is similar to lithology A of Elephant Moraine A79001 (EETA79001) in petrography and mineralogy, but is distinct in several aspects. Low-Ca pyroxenes in the Dar al Gani 476 groundmass are more magnesian (En76Fs21 Wo3∼En58Fs30Wo12) than those in lithology A of EETA79001 (En73Fs22Wo5∼En45Fs43Wo12), rather similar to pyroxenes in lherzolitic martian meteorites (En76Fs21 Wo3∼En63Fs22Wo15). Dar al Gani 476 olivine is less magnesian and shows a narrower compositional range (Fo76-58) than EETA79001 olivine (Fo81-53), and is also similar to olivines in lherzolitic martian meteorites (Fo74-65). The orthopyroxene-olivine-chromite xenolith typical in the lithology A of EETA79001 is absent in Dar al Gani 476. It seems that Dar al Gani 476 crystallized from a slightly more primitive mafic magma than lithology A of EETA79001 and several phases (olivine, pyroxene, chromite, and ilmenite) in Dar al Gani 476 may have petrogenetic similarities to those of lherzolitic martian meteorites. Olivine megacrysts in Dar al Gani 476 are in disequilibrium with the bulk composition. The presence of fractured olivine grains in which the most Mg-rich parts are in contact with the groundmass suggests that little diffusive modification of original olivine compositions occurred during cooling. This observation enabled us to estimate the cooling rates of Dar al Gani 476 and EETA79001 olivines, giving similar cooling rates of 0.03-3 °C/h for Dar al Gani 476 and 0.05-5 °C/h for EETA79001. This suggests that they were cooled near the surface (burial depth shallower than about 3 m at most), probably in lava flows during crystallization of groundmass. As is proposed for lithology A of EETA79001, it may be possible to consider that Dar al Gani 476 has an impact melt origin, a mixture of martian lherzolite and other martian rock (Queen Alexandra Range 94201, Nakhlites?).
Udry Arya - One of the best experts on this subject based on the ideXlab platform.
-
Caleta el Cobre 022 martian meteorite: increasing nakhlite diversity
'Wiley', 2020Co-Authors: Krämer Ruggiu Lisa, Udry Arya, Gattacceca Jérôme, Devouard Bertrand, Debaille Vinciane, Rochette Pierre, Lorand Jean-pierre, Bonal Lydie, Beck Pierre, Sautter ViolaineAbstract:International audienceCaleta el Cobre (CeC) 022 is a Martian meteorite of the nakhlite group, showing an unbrecciated cumulate texture, composed mainly of clinopyroxene and olivine. Augite shows irregular core zoning, euhedral rims, and thin overgrowths enriched in Fe relative to the core. Low‐Ca pyroxene is found adjacent to olivine. Phenocrysts of Fe‐Ti oxides are titanomagnetite with exsolutions of ilmenite/ulvöspinel. Intercumulus material consists of both coarse plagioclase and fine‐grained mesostasis, comprising K‐feldspars, pyroxene, apatite, ilmenite, Fe‐Ti oxides, and silica. CeC 022 shows a high proportion of Martian aqueous alteration products (iddingsite) in olivine (45.1 vol% of olivine) and mesostasis. This meteorite is the youngest nakhlite with a distinct Sm/Nd crystallization age of 1.215 ± 0.067 Ga. Its ejection age of 11.8 ± 1.8 Ma is similar to other Nakhlites. CeC 022 reveals contrasted cooling rates with similarities with faster cooled Nakhlites, such as Northwest Africa (NWA) 817, NWA 5790, or Miller Range 03346 Nakhlites: augite irregular cores, Fe‐rich overgrowths, fine‐grained K‐feldspars, quenched oxides, and high rare earth element content. CeC 022 also shares similarities with slower cooled Nakhlites, including Nakhla and NWA 10153: pyroxene modal abundance, pyroxenes crystal size distribution, average pyroxene size, phenocryst mineral compositions, unzoned olivine, and abundant coarse plagioclase. Moreover, CeC 022 is the most magnetic nakhlite and represents an analog source lithology for the strong magnetization of the Martian crust. With its particular features, CeC 022 must originate from a previously unsampled sill or flow in the same volcanic system as the other Nakhlites, increasing Martian sample diversity and our knowledge of Nakhlites
-
Caleta el Cobre 022 Martian Meteorite: Increasing Nakhlite Diversity
Digital Scholarship@UNLV, 2020Co-Authors: Ruggiu L. Krämer, Udry Arya, Gattacceca J., Devouard B., Rochette P., Lorand J. P., Bonal L., Beck P.Abstract:Caleta el Cobre (CeC) 022 is a Martian meteorite of the nakhlite group, showing an unbrecciated cumulate texture, composed mainly of clinopyroxene and olivine. Augite shows irregular core zoning, euhedral rims, and thin overgrowths enriched in Fe relative to the core. Low‐Ca pyroxene is found adjacent to olivine. Phenocrysts of Fe‐Ti oxides are titanomagnetite with exsolutions of ilmenite/ulvöspinel. Intercumulus material consists of both coarse plagioclase and fine‐grained mesostasis, comprising K‐feldspars, pyroxene, apatite, ilmenite, Fe‐Ti oxides, and silica. CeC 022 shows a high proportion of Martian aqueous alteration products (iddingsite) in olivine (45.1 vol% of olivine) and mesostasis. This meteorite is the youngest nakhlite with a distinct Sm/Nd crystallization age of 1.215 ± 0.067 Ga. Its ejection age of 11.8 ± 1.8 Ma is similar to other Nakhlites. CeC 022 reveals contrasted cooling rates with similarities with faster cooled Nakhlites, such as Northwest Africa (NWA) 817, NWA 5790, or Miller Range 03346 Nakhlites: augite irregular cores, Fe‐rich overgrowths, fine‐grained K‐feldspars, quenched oxides, and high rare earth element content. CeC 022 also shares similarities with slower cooled Nakhlites, including Nakhla and NWA 10153: pyroxene modal abundance, pyroxenes crystal size distribution, average pyroxene size, phenocryst mineral compositions, unzoned olivine, and abundant coarse plagioclase. Moreover, CeC 022 is the most magnetic nakhlite and represents an analog source lithology for the strong magnetization of the Martian crust. With its particular features, CeC 022 must originate from a previously unsampled sill or flow in the same volcanic system as the other Nakhlites, increasing Martian sample diversity and our knowledge of Nakhlites
-
Martian magmatism from plume metasomatized mantle
'Springer Science and Business Media LLC', 2018Co-Authors: Day James, Udry Arya, Tait Kimberly, Moynier Frédéric, Liu Yang, Neal CliveAbstract:International audienceDirect analysis of the composition of Mars is possible through delivery of meteorites to Earth. Martian meteorites include ∼165 to 2400 Ma shergottites, originating from depleted to enriched mantle sources, and ∼1340 Ma Nakhlites and chassignites, formed by low degree partial melting of a depleted mantle source. To date, no unified model has been proposed to explain the petrogenesis of these distinct rock types, despite their importance for understanding the formation and evolution of Mars. Here we report a coherent geochemical dataset for shergottites, Nakhlites and chassignites revealing fundamental differences in sources. Shergottites have lower Nb/Y at a given Zr/Y than Nakhlites or chassignites, a relationship nearly identical to terrestrial Hawaiian main shield and rejuvenated volcanism. Nakhlite and chassignite compositions are consistent with melting of hydrated and meta-somatized depleted mantle lithosphere, whereas shergottite melts originate from deep mantle sources. Generation of martian magmas can be explained by temporally distinct melting episodes within and below dynamically supported and variably metasomatized lithosphere, by long-lived, static mantle plumes
Francis M. Mccubbin - One of the best experts on this subject based on the ideXlab platform.
-
The chlorine isotopic composition of Martian meteorites 1: Chlorine isotope composition of Martian mantle and crustal reservoirs and their interactions
Meteoritics & Planetary Science, 2016Co-Authors: J. T. Williams, Francis M. Mccubbin, Charles K. Shearer, Carl B. Agee, Zachary D. Sharp, Paul V. Burger, A. R. Santos, Kevin D. MckeeganAbstract:The Martian meteorites record a wide diversity of environments, processes, and ages. Much work has been done to decipher potential mantle sources for Martian magmas and their interactions with crustal and surface environments. Chlorine isotopes provide a unique opportunity to assess interactions between Martian mantle-derived magmas and the crust. We have measured the Cl-isotopic composition of 17 samples that span the range of known ages, Martian environments, and mantle reservoirs. The 37Cl of the Martian mantle, as represented by the olivine-phyric shergottites, NWA 2737 (chassignite), and Shergotty (basaltic shergottite), has a low value of approximately −3.8‰. This value is lower than that of all other planetary bodies measured thus far. The Martian crust, as represented by regolith breccia NWA 7034, is variably enriched in the heavy isotope of Cl. This enrichment is reflective of preferential loss of 35Cl to space. Most basaltic shergottites (less Shergotty), Nakhlites, Chassigny, and Allan Hills 84001 lie on a continuum between the Martian mantle and crust. This intermediate range is explained by mechanical mixing through impact, fluid interaction, and assimilation-fractional crystallization.
-
a petrogenetic model for the comagmatic origin of chassignites and Nakhlites inferences from chlorine rich minerals petrology and geochemistry
Meteoritics & Planetary Science, 2013Co-Authors: Francis M. Mccubbin, Stephen M. Elardo, Charles K. Shearer, Alexander Smirnov, Erik H. Hauri, David S. DraperAbstract:Twelve samples belonging to the chassignite and nakhlite subgroups of Martian meteorites were investigated using a variety of micro-beam analytical techniques to gain insight into the petrogenesis of these two meteorite classes. There are a striking number of geochemical similarities between the chassignites and Nakhlites, including mineralogy and petrology, crystallization age, cosmic-ray exposure age, and radiogenic isotopic compositions. However, there are also geochemical differences, namely in trace element systematics of pyroxenes, that have led some authors to conclude that the Nakhlites are comagmatic with each other, but not comagmatic with the chassignites. On the basis of data presented here, we propose a model in which these differences can be reconciled by the addition of an exogenous Cl-rich fluid to the chassignite-nakhlite magma body shortly after the formation of the cumulate horizon that was sampled by the Chassigny meteorite. This model is supported by the textural and chemical associations of the volatile-bearing minerals apatite, amphibole, and biotite, which record a history starting with the addition of a Cl- and LREE-enriched fluid to the magma body. As the magma continued to crystallize, it eventually reached chloride saturation and degassed a Cl-rich fluid phase. Depending on the provenance of the Cl-rich fluid, this model could explain how the chassignites and Nakhlites originated from an LREE-depleted source, yet all exhibit LREE-enriched bulk-rock patterns. Additionally, the model explains the range in oxygen fugacity that is recorded by the chassignites and Nakhlites because eventual exsolution and loss of Cl-rich fluid phases near the end of crystallization of the nakhlite sequence leads to auto-oxidation of the magma body due to the preferential partitioning of Fe 2+ into the fluid phase.
-
Unique Meteorite from Early Amazonian Mars: Water-Rich Basaltic Breccia Northwest Africa 7034
Science (New York N.Y.), 2013Co-Authors: Carl B. Agee, Francis M. Mccubbin, R. Shaheen, Nicole V. Wilson, Karen Ziegler, Victor J. Polyak, Zachary D. Sharp, Yemane Asmerom, Morgan H. Nunn, Mark H. ThiemensAbstract:We report data on the martian meteorite Northwest Africa (NWA) 7034, which shares some petrologic and geochemical characteristics with known martian meteorites of the SNC (i.e., shergottite, nakhlite, and chassignite) group, but also has some unique characteristics that would exclude it from that group. NWA 7034 is a geochemically enriched crustal rock compositionally similar to basalts and average martian crust measured by recent Rover and Orbiter missions. It formed 2.089 ± 0.081 billion years ago, during the early Amazonian epoch in Mars9 geologic history. NWA 7034 has an order of magnitude more indigenous water than most SNC meteorites, with up to 6000 parts per million extraterrestrial H2O released during stepped heating. It also has bulk oxygen isotope values of Δ17O = 0.58 ± 0.05 per mil and a heat-released water oxygen isotope average value of Δ17O = 0.330 ± 0.011 per mil, suggesting the existence of multiple oxygen reservoirs on Mars.
