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At least 109 records · Page 6
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NASA NTRS1993

Nitrogen and noble gases in a glass sample from the LEW88516 shergottite

A glass separate from the LEW88516 shergottite was analyzed by step-wise combustion for N and noble gases to determine whether it contained trapped gas similar in composition to the martian atmosphere-like component previously observed in lithology C of EETA79001. Excesses of Ar-40 and Xe-129 were in fact observed in this glass, although the amounts of these excesses less than or = to 20% of those seen in the latter meteorite, and are comparable to the amounts seen in whole-rock analyses of LEW88516. The isotopic composition of N in LEW88516 does not show an enrichment in delta N-15 commensurate with the amount of isotopically-heavy N expected from the noble gases excesses. One must posit some extreme assumptions about the nature of the N components present in LEW88516 in order to allow the presence of the trapped nitrogen component. Alternatively, the N has somehow been decoupled from the noble gases, and was either never present of has been lost.

Becker, Richard H.↗
NASA NTRS1997

Constraints on Martian Differentiation Processes from Rb-Sr and Sm-Nd Isotopic Analyses of the Basaltic Shergottite QUE 94201

Isotopic analyses of mineral, leachate, and whole rock fractions from the Martian shergottite meteorite QUE 94201 yield Rb-Sr and Sm-Nd crystallization ages of 327 +/- 12 and 327 +/- 19 Ma, respectively. These ages are concordant, although the isochrons are defined by different fractions within the meteorite. Comparison of isotope dilution Sm and Nd data for the various QUE 94201 fractions with in situ ion microprobe data for QUE 94201 minerals from the literature demonstrate the presence of a leachable crustal component in the meteorite. This component is likely to have been added to QUE 94201 by secondary alteration processes on Mars, and can affect the isochrons by selectively altering the isotopic systematics of the leachates and some of the mineral fractions. The absence of crustal recycling processes on Mars may preserve the geochemical evidence for early differentiation and the decoupling of the Rb-Sr and Sm-Nd isotopic systems, underscoring one of the fundamental differences between geologic processes on Mars and the Earth.

Borg, Lars E.↗
NASA NTRS2002

An "Andestic" Component in Shergottites with Restored LREE Abundances?

The shergottite Martian meteorites present a variety of oft-confusing petrologic features. In particular, represented among this subgroup are basalts with very depleted LREE abundances, as well as those with nearly chondritic overall REE abundances. The LREE-depleted basalts appear to more closely record the REE and isotopic features of their mantle source regions. Those basalts with more nearly chondritic REE abundances appear to contain an extra component often referred to as a "crustal" component. The addition of the crustal component tends to restore the overall REE abundance pattern towards chondritic relative abundances. Here we suggest that the crustal component could derive from "andesitic" rocks observed remotely to occur on the Martian surface, and which were analysed at the Pathfinder site.

Nyquist, L. E.↗
NASA NTRS2002

An "Andesitic" Component in Shergottites with Restored LREE Abundances?

The shergottite Martian meteorites present a variety of oft-confusing petrologic features. In particular, represented among this subgroup are basalts with very depleted LREE abundances, as well as those with nearly chondritic overall REE abundances. The LREE-depleted basalts appear to more closely record the REE and isotopic features of their mantle source legions. Those basalts with more nearly chondritic REE abundances appear to contain an extra component often referred to as a "crustal" component. The addition of the crustal component tends to restore the overall REE abundance pattern towards chondritic relative abundances. Here we suggest that the crustal component could derive from andesitic rocks observed remotely to occur on the Martian surface, and which were analysed at the Pathfinder site.

Nyquist, L. E.↗
NASA NTRS2005

Experimental Petrology of the Basaltic Shergottite Yamato 980459: Implications for the Thermal Structure of the Martian Mantle

Yamato 980459 (Y98) is an olivine-phyric basaltic shergottite composed of 48% pyroxene, 26% olivine, 25% mesostasis, and 1% other minerals. Unlike the other Martian basalts, it contains no plagioclase. Olivine in Y98 is the most magnesian of all Martian meteorites. Thus Y98 is believed to be the most primitive and its composition may be the closest to a primary or direct melt of the Martian mantle. As such, it provides a very useful probe of the mineralogy and depth of its mantle source region. Toward this end, we are conducting crystallization experiments on a synthetic Y98 composition at Martian mantle pressures and temperatures.

Dalton, H. A.↗
NASA NTRS2005

APXS ANALYSES OF BOUNCE ROCK: THE FIRST SHERGOTTITE ON MARS

During the MER Mission, an isolated rock at Meridiani Planum was analyzed by the Athena instrument suite [1]. Remote sensing instruments noticed its distinct appearance. Two areas on the untreated rock surface and one area that was abraded with the Rock Abrasion Tool were analyzed by Microscopic Imager, Mossbauer Mimos II [2], and Alpha Particle X-ray Spectrometer (APXS). Results of all analyses revealed a close relationship of this rock with known basaltic shergottites.

Ming, Douglas W.↗
NASA NTRS2006

Ar-Ar Age of NWA-1460 and Evidence For Young Formation Ages of the Shergottites

Agreement of Ar-Ar, Sm-Nd, and Rb-Sr ages for NWA1460, and the inconsistency between a low shock-heating temperature for Zagami and the proposition that a 4.0 Gyr-old Zagami lost most of its Ar-40 are inconsistent with ancient formation ages for these shergottites, but are consistent with relatively young igneous formation ages.

Bogard, Donald D.↗
NASA NTRS2007

Lu-Hf and Sm-Nd Isotopic Studies of Shergottites and Nakhlites: Implications for Martian Mantle Sources

We present a new Lu-Hf and Sm-Nd isotope systematics study of four enriched shergottites (Zagami, Shergotty, NWA856 and Los Angeles), and three nakhlites (Nakhla, MIL03346 and Yamato 000593) in order to further understand processes occurring during the early differentiation of Mars and the crystallization of its magma ocean. Two fractions of the terrestrial petrological analogue of nakhlites, the Archaean Theo's flow (Ontario, Canada) were also measured. The coupling of Nd and Hf isotopes provide direct insights on the mineralogy of the melt sources. In contrast to Sm/Nd, Lu/Hf ratios can be very large in minerals such as garnet. Selective partial melting of garnet bearing mantle sources can therefore lead to characteristic Lu/Hf signatures that can be recognized with Hf-176/Hf-177Hf ratios.

Debaille, V.↗
NASA NTRS2008

Petrology and Mineral Chemistry of New Olivine-Phyric Shergottite RBT04262

RBT04262 was found by the 2004-2005 ANSMET team at the Roberts Massif in Antarctica. It is paired with RBT04261 and is classified as an olivine-phyric shergottite. RBT04261 is 4.0 x 3.5 x 2.5 cm and 78.8 g, and RBT04262 is 6.5 x 5.5 x 3.5 cm and 204.6 g. Both were partially covered by a fusion crust [1]. Chemical analysis and mapping of this meteorite was performed using the Cameca SX100 electron microprobe at NASA Johnson Space Center.

Dalton, H. A.↗
NASA NTRS2008

Sulfur and Iron Speciation in Gas-rich Impact-melt Glasses from Basaltic Shergottites Determined by Microxanes

Sulfur is abundantly present as sulfate near Martian surface based on chemical and mineralogical investigations on soils and rocks in Viking, Pathfinder and MER missions. Jarosite is identified by Mossbauer studies on rocks at Meridian and Gusev, whereas MgSO4 is deduced from MgO - SO3 correlations in Pathfinder MER and Viking soils. Other sulfate minerals such as gypsum and alunogen/ S-rich aluminosilicates and halides are detected only in martian meteorites such as shergottites and nakhlites using SEM/FE-SEM and EMPA techniques. Because sulfur has the capacity to occur in multiple valence states, determination of sulfur speciation (sulfide/ sulfate) in secondary mineral assemblages in soils and rocks near Mars surface may help us understand whether the fluid-rock interactions occurred under oxidizing or reducing conditions. To understand the implications of these observations for the formation of the Gas-rich Impact-melt (GRIM) glasses, we determined the oxidation state of Fe in the GRIM glasses using Fe K micro-XANES techniques.

Sutton, S. R.↗
NASA NTRS2009

Sulfur Speciation in the Martian Regolith Component in Shergottite Glasses

We have shown that Gas-Rich Impact-Melt (GRIM) glasses in Shergotty, Zagami, and EET79001 (Lith A and Lith B) contain Martian regolith components that were molten during impact and quenched into glasses in voids of host rock materials based on neutron-capture isotopes, i.e., Sm-150 excesses and Sm-149 deficits in Sm, and Kr-80 excesses produced from Br [1, 2]. These GRIM glasses are rich in S-bearing secondary minerals [3.4]. Evidence for the occurrence of CaSO4 and S-rich aluminosilicates in these glasses is provided by CaO-SO3 and Al2O3-SO3 correlations, which are consistent with the finding of gypsum laths protruding from the molten glass in EET79001 (Lith A) [5]. However, in the case of GRIM glasses from EET79001 (Lith B), Shergotty and Zagami, we find a different set of secondary minerals that show a FeO-SO3 correlation (but no MgOSO3 correlation), instead of CaO-SO3 and Al2O3-SO3 correlations observed in Lith A. These results might indicate different fluidrock interactions near the shergottite source region on Mars. The speciation of sulfur in these salt assemblages was earlier studied by us using XANES techniques [6], where we found that Lith B predominantly contains Fe-sulfide globules (with some sulfate). On the other hand, Lith A showed predominantly Casulfite/ sulfate with some FeS. Furthermore, we found Fe to be present as Fe2+ indicating little oxidation, if any, in these glasses. To examine the sulfide-sulfate association in these glasses, we studied their Fe/Ni ratios with a view to find diagnostic clues for the source fluid. The Fe-sulfide mineral (Fe(0.93)Ni(0.3)S) in EET79001, Lith A is pyrrhotite [7, 8]. It yields an Fe/Ni ratio of 31. In Shergotty, pyrrhotite occurs with a molar ratio of Fe:S of 0.94 and a Ni abundance of 0.12% yielding a Fe/Ni ratio of approx.500 [8]. In this study, we determined a NiO content of approx.0.1% and FeO/NiO ratio of approx.420 in S-rich globules in #507 (EET79001, Lith B) sample using FE-SEM. In the same sample (bulk), using EMPA, we determined a FeO/NiO ratio of approx.700 (raster mode). Using similar techniques, we determined a NiO content of approx.0.015% and a FeO/NiO ratio of approx.800 in #506 (EET79001, Lith A). Moreover, a NiO content of approx.150 ppm and 6.1% FeO were found in Lith A GRIM glasses using neutron activation analysis [9] yielding a FeO/NiO ratio of approx.420. The FeO/NiO ratios in secondary mineral phases in S-rich pockets of EET79001 (Lith A/B) and Shergotty are high (approx.400) compared to the FeO/NiO ratio of 31 in Lith A pyrrhotite. These results suggest similar kind of fluids interacted with different rock materials to yield the observed variations in GRIM glasses in EET79001 Lith A and B.

Rao, M. N.↗
NASA NTRS2011

Recognizing the Effects of Terrestrial Contamination on D/H Ratios in Shergottite Phosphates

Hydrogen isotope ratios in shergottite phosphate minerals have been investigated by SIMS in the meteorites Queen Alexandra Range (QUE) 94201 and Los Angeles. We have also collected electron probe data on these phosphates in order to characterize the phosphate minerals and attempt to document any potential hydrogen isotopic differences between chlor-apatite and whitlockite. In the section of Los Angeles we studied (748), we found both chlor-apatite and whitlockite, but in the section of QUE 94201,38 studied, we found only whitlockite. In both meteorites, D/H ratios (expressed in units of delta D (sub SMOW) vary, from terrestrial values up to approximately 5400%o in QUE 94201, and to approximately 3800%o in Los Angeles. We have carefully examined the ion probed pits with high-resolution FE-SEM. In most cases where the D/H ratios are low, we have iden-tified cracks that instersect the ion probe pit. These cracks are not visible in the optical microscope attached to the SIMS instument, making them impossible to avoid during SIMS data collection. We contend that the low ratios are a function of substantial terrestrial contamination, and that similar contamination is a likely factor in previously published studies on D/H ratios in martian phosphates. Here we highlight the difficulty of attempts to constrain the martian mantle D/H ratio using phosphate data, given that both terrestrial contamination and martian mantle hydrogen will move phosphate D/H ratios in the same direction, toward lower values. We note that our data include some of the most deuterium-rich values ever reported for martian phosphates. It is clear that some of our measurements are only minimally or totally uncontaminated, but the question arises, are intermediate values diminished because of true martian variability, or do they reflect contamination?

Ross, D. K.↗
NASA NTRS2011

Stabile Chlorine Isotope Study of Martian Shergottites and Nakhlites; Whole Rock and Acid Leachates and Residues

We have established a precise analytical technique for stable chlorine isotope measurements of tiny planetary materials by TIMS (Thermal Ionization Mass Spectrometry) [1], for which the results are basically consistent with the IRMS tech-nique (gas source mass spectrometry) [2,3,4]. We present here results for Martian shergottites and nakhlites; whole rocks, HNO3-leachates and residues, and discuss the chlorine isotope evolution of planetary Mars.

Nakamura, N.↗
NASA NTRS2012

Laboratory Shock Experiments on Basalt - Iron Sulfate Mixes at Approximately 40-50 GPa and Their Relevance to the Martian Regolith Component Present in Shergottites

Basaltic shergottites such as Shergotty, Zagami and EET79001 contain impact melt glass pockets that are rich in Martian atmospheric gases [1] and are known as gas-rich impact-melt (GRIM) glasses. These glasses show evidence for the presence of a Martian regolith component based on Sm and Kr isotopic studies [2]. The GRIM glasses are sometimes embedded with clusters of innumerable micron-sized iron-sulfide blebs associated with minor amounts of iron sulfate particles [3, 4]. These sulfide blebs are secondary in origin and are not related to the primary igneous sulfides occurring in Martian meteorites. The material comprising these glasses arises from the highly oxidizing Martian surface and sulfur is unlikely to occur as sulfide in the Martian regoilith. Instead, sulfur is shown to occur as sulfate based on APXS and Mossbauer results obtained by the Opportunity and Spirit rovers at Meridiani and Gusev [5]. We have earlier suggested that the micron-sized iron sulfide globules in GRIM glasses were likely produced by shock-reduction of iron sulfate occurring in the regolith at the time when the GRIM glasses were produced by the meteoroid impact that launched the Martian meteorites into space [6]. As a result of high energy deposition by shock (approx. 40-60 GPa), the iron sulfate bearing phases are likely to melt along with other regolith components and will get reduced to immiscible sulfide fluid under reducing conditions. On quenching, this generates a dispersion of micron-scale sulfide blebs. The reducing agents in our case are likely to be H2 and CO which were shock-implanted from the Martian atmosphere into these glasses along with the noble gases. We conducted lab simulation experiments in the Lindhurst Laboratory of Experimental Geophysics at Caltech and the Experimental Impact Laboratory at JSC to test whether iron sulfide globules can be produced by impact-driven reduction of iron sulfate by subjecting Columbia River Basalt (CRB) and ferric sulfate mixtures to shock pressures between 40 and 50 GPa under reducing conditions. The experimental products from the recovered samples were analyzed by SEM and microprobe techniques at JSC.

Rao, M. N.↗
NASA NTRS2012

Complex Formation History of Highly Evolved Basaltic Shergottite, Zagami

Zagami, a basaltic shergottite, contains several kinds of lithologies such as Normal Zagami consisting of Fine-grained (FG) and Coarse-grained (CG), Dark Mottled lithology (DML), and Olivine-rich late-stage melt pocket (DN). Treiman and Sutton concluded that Zagami (Normal Zagami) is a fractional crystallization product from a single magma. It has been suggested that there were two igneous stages (deep magma chamber and shallow magma chamber or surface lava flow) on the basis of chemical zoning features of pyroxenes which have homogeneous Mg-rich cores and FeO, CaO zoning at the rims. Nyquist et al. reported that FG has a different initial Sr isotopic ratio than CG and DML, and suggested the possibility of magma mixing on Mars. Here we report new results of petrology and mineralogy for DML and the Olivine-rich lithology (we do not use DN here), the most evolved lithology in this rock, to understand the relationship among lithologies and reveal Zagami s formation history

Niihara, T.↗
NASA NTRS2012

Nanosims Imaging of Volatile Elements (H, C, F and S) in Shergottites

Volatiles, especially water, play a critical role in the evolution of Mars and other planetary bodies. Though the detection limit and spatial resolution in measuring volatiles in different phases of Martian meteorites have been greatly improved using ion microprobes (SIMS), it remains a challenge to accurately determine volatile concentrations due to contamination by terrestrial volatiles. Most Martian meteorites experienced cracking and shattering from the high-pressure shock either on the Martian surface and/or when coming to Earth. Martian meteorites generally contain volatiles in cracks even after careful sample preparation for SIMS analysis. We used the Cameca NanoSIMS 50L at Carnegie Institution of Washington to image volatile (H, C, F and S) distributions in two shergottite meteorites, LAR 06319 (L2) and Y-980456 (Y3). The mapping of volatiles in these meteorites greatly assisted us in understanding the distribution of volatile contamination and in improving future volatile measurement methods

Wang, J.↗