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Marti, K.

Publications and source records attributed to Marti, K..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

U-Pb Dating of Zircons and Phosphates in Lunar Meteorites, Acapulcoites and Angrites

Zircon U-Pb geochronology has made a great contribution to the timing of magmatism in the early Solar System [1-3]. Ca phosphates are another group of common accessory minerals in meteorites with great potential for U-Pb geochronology. Compared to zircons, the lower closure temperatures of the U-Pb system for apatite and merrillite (the most common phosphates in achondrites) makes them susceptible to resetting during thermal metamorphism. The different closure temperatures of the U-Pb system for zircon and apatite provide us an opportunity to discover the evolutionary history of meteoritic parent bodies, such as the crystallization ages of magmatism, as well as later impact events and thermal metamorphism. We have developed techniques using the Cameca IMS-1280 ion microprobe to date both zircon and phosphate grains in meteorites. Here we report U-Pb dating results for zircons and phosphates from lunar meteorites Dhofar 1442 and SaU 169. To test and verify the reliability of the newly developed phosphate dating technique, two additional meteorites, Acapulco, obtained from Acapulco consortium, and angrite NWA 4590 were also selected for this study as both have precisely known phosphate U-Pb ages by TIMS [4,5]. Both meteorites are from very fast cooled parent bodies with no sign of resetting [4,5], satisfying a necessity for precise dating.

Zhou, Q.↗
NASA NTRS2004

Signatures in Martian Volatiles and the Magma Sources of NC Meteorites

We report nitrogen and xenon isotopic signatures in Yamato nakhlites and use the data to assess properties of the magma source of NC meteorites in planet Mars. The Chassigny meteorite was investigated by Floran et al, who classified it as a cumulate dunite with hydrous amphibole-bearing melt inclusions with no preferred orientation of the olivines. Their inferred composition of the parent magma, which was based on electron microprobe analyses, has been questioned. The trace and minor elements in minerals were analyzed in nakhlites and in Chassigny and the authors conclude that nakhlites may represent samples from different horizons of the same lithologic unit, but that Chassigny was not co-magmatic with the nakhlites.

Marti, K.↗
NASA NTRS2004

Calibration of the Galactic Cosmic Ray Flux

We report first Xe data on the cross-calibration of I-129-Xe-129(sub n) ages with conventional CRE ages, a method which is expected to provide information on the long-term constancy of the galactic cosmic ray (GCR) flux. We studied isotopic signatures of Xe released in stepwise heating, decomposition and melting of troilites in the Cape York iron meteorite to identify isotopic shifts in Xe-129 and Xe-131 due to neutron capture in Te-128 and Te-130. We also resolve components due to extinct 129I, spallation and fission Xe. There has recently been much speculation on the constancy of GCR over long time scales, as may be inferred from iron meteorites. If GCRs originate from supernova events, this provides the basis for postulating increased fluxes at locations with higher than average densities of supernovae, specifically in OB-associations. The solar system at present appears to be inside a local bubble between spiral arms and may experience an increased GCR flux.

Mathew, K. J.↗
NASA NTRS2002

Near-Earth Asteroid Origin for the Farmington Meteorite

We report nitrogen and xenon isotopic signatures in separated metal and non-magnetic phases of a catastrophically degassed L5 chondrite and discuss implications for the collisional event and the impactor. Additional information is contained in the original extended abstract.

Marti, K.↗
NASA NTRS2002

Fission Xenon on Mars

Fission Xe components due to Pu-244 decay in the early history of Mars have been identified in nakhlites; as in the case of ALH84001 and Chassigny the fission gas was assimilated into indigenous solar-type Xe. Additional information is contained in the original extended abstract.

Mathew, K. J.↗
NASA NTRS2000

Leonids: Did They Make it to Earth?

On the morning of November 18. 1998, following the spectacular Leonid meteor shower, one of us (S. De) found particles spread over the roof terrace in a residence in Baruipur. a suburb of Calcutta, India. Considering the time and location, these particles possibly derived from the meteor shower, although the fall was not observed. Other particles collected in connection with the Leonid showers in different parts of India proved to be of terrestrial origin.

Weigel, A.↗
NASA NTRS1994

Nitrogen and xenon isotopic disequilibrium in Bachmut (L6) chondrule J2689 and matrix

Chondrule J2689, a large (8-mm) RP chondrule from Bachmut (L6) was previously found to be in disequilibrium with its host in a variety of features: (1) It has a fine-grained hornfelsic texture; (2) it contains low amounts of metal with a low-Ni taenite composition not found in the matrix; (3) the Ni/Co ratio of that metal is close to the solar ratio, which is equal to the bulk Ni/Co ratio (23) of the chondrule; (4) the bulk alkali content of the chondrule is high and the Na/K ratio is fractionated with respect to the average L chondrite ratio of 8; (5) Cr is depleted in spite of the high pyroxene content; (6) the siderophile elements are strongly depleted but are fractionated with their abundances increasing with volatility; and (7) the O isotopes of the chondrule and the host are out of equilibrium. However, the (Fe,Mg) silicates, feldspar, and chromite have chemical compositions indistinguishable from that of the host chondrite. We have studied a chip of the chondrite and of adjacent matrix by stepwise heating and by combustion in O for N and Xe isotopic abundances. (1) The chondrule preserved distinct bulk, metal, and O isotopic compositional features. It is therefore unlikely that the 'equilibration' of the major silicates Fe/Mg ratios could have taken place after accretion; (2) the chondrule was well equilibrated before break-up and exposure to cosmic rays; (3) two N signatures in the matrix also indicate that the matrix is not equilibrated; and (4) all data collected so far point toward the presence of unequilibrated Bachmut components. Very few reactions took place after accretion.

Kim, Y.↗
NASA NTRS1993

A calibration of the production rate ratio P-21/P-26 by low energy secondry neutrons: Identification of Ne spallation components at the 10(exp 6) atoms/g level in terrestrial samples

The spallation ratio (Ne-22/Ne-21)(sub c) from Si was determined as 1.243 plus or minus 0.022 in a terrestrial quartz sample. We carried out a calibration of the in-situ production rate ratio P-21/P-26 in quartz samples for which Be-10 and Al-26 production rates were previously measured. A ratio P-21/P-26 of 0.67 plus or minus 0.12 is obtained.

Graf, TH.↗
NASA NTRS1993

Isotopic signatures and distribution of nitrogen and trapped and radiogenic xenon in the Acapulco and FRO90011 meteorites

Acapulco metal and silicate show distinct N isotopic signatures. Trapped heavy noble gases are carried by 'magnetic' opx and radiogenic Xe-129 excesses are observed in phosphate and in minor surficial phases on metal grains. N and Xe isotopic signatures in FRO90011 do not agree with those observed in Acapulco. The Acapulco meteorite is unique in having achondritic texture and chondritic composition. Its mineralogical study shows the record of high temperature (1100 C) recrystallization. However, this meteorite shows abundances of volatile elements close to the levels observed in carbonaceous chondrites and concentrations of heavy noble gases comparable to those observed in type 4 ordinary chondrites, not expected for a presumed highly equilibrated object. Nitrogen measurements in bulk Acapulco revealed two different isotopic signatures, in apparent conflict with evidence for a high degree of recrystallization. N and Xe were studied in separated mineral phases to search for the carriers in order to better understand the formation and thermal history of the Acapulco parent body.

Kim, Y.↗
NASA NTRS1993

Low-energy ion implantation: Large mass fractionation of argon

The isotropic signatures of noble gases in the atmospheres of the Earth and other planets are considerably evolved when compared to signatures observed in the solar wind. The mechanisms driving the evolution of planetary volatiles from original compositions in the solar accretion disk are currently poorly understood. Modeling of noble-gas compositional histories requires knowledge of fractionating processes that may have operated through the evolutionary stages. Since these gases are chemically inert, information on noble-gas fractionation processes can be used as probes. The importance of understanding these processes extends well beyond 'noble-gas planetology.' Trapped argon acquired by low-energy implantation (approximately less than 100 eV) into solids is strongly mass fractionated (approximately greater than or equal to 3 percent/amu). This has potential implications for the origin and evolution of terrestrial planet atmospheres.

Ponganis, K. V.↗
NASA NTRS1992

Compositional trends in rock-forming elements of Comet Halley dust

The VEGA 1 and 2 spacecraft flew by Comet P/Halley in 1986 carrying, among other instruments, two mass spectrometers to measure the elemental composition of dust particles emitted from the comet. Most particles seem to be a mixture of silicates of variable magnesium-iron composition and organic matter. Comprehensive study of data and consideration of the mass of dust particles reveal cometary grains of 'unusual' composition: magnesium-rich and iron-rich particles. Magnesium-rich particles are most likely magnesium carbonates, which could not have formed under conditions of equilibrium condensation but rather require formation by aqueous alteration. The composition of the iron-rich particles can also be related to secondary processes in the comet.

Fomenkova, M. N.↗
NASA NTRS1992

Search for Cm-248 in the early solar system

Possible evidence for the presence of Cm-248 in the early solar system was reported from fission gas studies (Rao and Gopalan, 1973) and recently from studies of very high nuclear track densities (not less than 5 x 10 exp 8/sq cm) in the merrillite of the H4 chondrite Forest Vale (F.V.) (Pellas et al., 1987). We report here an analysis of the isotopic abundances of xenon in F.V. phosphates and results of track studies in phosphate/pyroxene contacts. The fission xenon isotopic signature clearly identifies Pu-244 as the extinct progenitor. We calculate an upper limit Cm-248/Pu-244 to be less than 0.0015 at the beginning of Xe retention in F.V. phosphates. This corresponds to an upper limit of the ratio Cm-248/U-235 of not greater than 5 x 10 exp -5 further constraining the evidence for any late addition of freshly synthesized actinide elements just prior to solar system formation. The fission track density observed after annealing the phosphates at 290C (1 hr, which essentially erases spallation recoil tracks) is also in agreement with the Pu-244 abundance inferred from fission Xe. The spallation recoil tracks produced during the 76 Ma cosmic-ray exposure account for the very high track density in merrillites.

Lavielle, B.↗
NASA NTRS1992

On the isotopic signature of recent solar-wind nitrogen

One of the most intriguing discoveries yielded by the Apollo samples was evidence pointing towards a significant long-term change in the composition of the sun. Such a change, of the size inferred from the lunar sample data, is inconsistent with present theories of solar evolution. Consequently, there is much interest in exploring this phenomenon as closely as possible, to determine exactly what compositional changes have taken place and whether those changes really did take place in the sun, or whether the cause lies elsewhere. The reason why we can use the moon to analyze the elements in the sun is that the sun emits a stream of ions, known as the solar wind, whose composition, on average, is believed to be the same as that in the surface regions of the sun. When the solar-wind ions hit the surface of the moon, many of them penetrate a short distance into the dust grains lying on the lunar surface. Thus, after a grain has sat on the lunar surface for a while, it has a rim of material that is partly lunar and partly solar in composition. For most chemical elements, the difference between lunar and solar composition is so sufficiently small that the solar elements cannot be detected, but for a handful of elements that are missing from the moon, their solar 'signature' can be observed in samples of lunar soil brought back by the astronauts. Among those elements is nitrogen, the most common element in the air we breathe, but very rare indeed on the moon. Our analytical techniques are not sophisticated enough yet to enable us to analyze individual lunar soil grains for nitrogen, much less to zero in on just the nitrogen in the surface of such a grain. Consequently we are forced to analyze samples consisting of many different grains, each of which could have experienced its own individual history. This makes it difficult to identify the nitrogen implanted in grain surfaces, and also to define the age of a sample.

Kim, Y.↗
NASA NTRS1992

Solar-type xenon - Isotopic abundances in Pesyanoe

Elemental and isotopic abundances of Ar and Xe were measured in three grain-size separates in the dark phase of the enstatite achondrite Pesyanoe by stepwise heating, using a combination of pyrolysis and combustion steps. The data reveal a low-temperature gas fraction with Ar/Xe ratios close to the solar ratio and isotopically similar to solar-type Ar and Xe observed in lunar samples. The gas released at intermediate temperature steps shows that Ar and Xe are isotopically fractionated, compared to the low-temperature components. Pesyanoe does not have excess Ar-40 and fission Xe, which means its parent body was too small for ion reimplantation. It is concluded that solar-type Xe isotopic abundances can be inferred from the low-temperature component. A comparison of Pesyanoe and lunar data shows that isotopic signatures of solar-wind Xe, as sampled at two different points in solar system space and time, are identical within experimental error.

Kim, J. S.↗
NASA NTRS1992

Evolution of isotopic signatures in lunar-regolith nitrogen - Noble gases and nitrogen in grain-size fractions from regolith breccia 79035

Ilmenite and pyroxene grain-size separates from 79035 were analyzed for trapped N; the ilmenite was also analyzed for trapped Xe. Ilmenite N contains two or more isotopically distinct trapped components differing in release temperature and therefore plausibly in implantation energy. The isotopically light, higher-temperature (higher-energy?) component has a delta N-15 value equal to -180 percent, significantly above the minimum value observed in bulk 79035, suggesting that parts of 79035 were exposed on the lunar surface earlier than the ilmenite. Using trapped Ar-40/Ar-36 and cosmogenic Ne-21 (Benkert, 1989) a compaction age of about 1 Ga was derived for the ilmenite. This implies a considerably more recent exposure than previously thought, and suggests that the long-term change in delta N-15 of regolith N was more rapid than generally believed. Comparison of these results with those for black/orange glass from 74001/74002 (compaction age 3.7 Ga; delta N-15 in the range -36 to +18 percent (Kerridge et al., 1991) indicates that the long-term trend may have followed a complex evolutionary path. Data for 79035 pyroxenes are consistent with the ilmenite compaction age but suggest a more complex exposure history.

Kerridge, J. F.↗