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Abhijit BASU David S. McKAY Richard V. MORRIS Susan J. WENTWORTH 《Meteoritics & planetary science》1996,31(6):777-782
Abstract— We report results of our investigation of the relationship between values of Is/FeO (relative concentration of nanophase Fe0 divided by total FeO content), glass abundance, total Fe content, and degree of digestion of <20 μm clasts for 22 individual agglutinates (250–1000 μm) from the mature Apollo 16 soil 61181 (Is/FeO = 82 units in the <250 μm fraction). Agglutinates are important products of space weathering on the Moon, and they influence spectral observations at visible and near-IR wavelengths. Values of Is/FeO for individual agglutinates (250–1000 μm) within this single soil span a range from 3 to 262 units which is larger than the range observed for all Apollo 16 bulk soils (～0 to 110 units). No correlation was observed between Is/FeO and glass abundance and FeO concentrations for either agglutinitic glass or whole agglutinate particles under investigation. Our results suggest that the variation in Is/FeO for agglutinates from a single soil may be in part a consequence of natural mixing processes on the Moon that produce highly-variable environments (with respect to surface exposure) for agglutinate formation and in part to variable kinetics of reactions in an agglutinate melt, which are influenced by a variety of factors including melt composition, temperature, impactor velocity, and quench rate. We cannot exclude but do not see evidence for other processes including addition of exotic agglutinates, micrometeoritic bombardment into compositionally-diverse microtargets, recycling of agglutinates, preferential melting of very fine soil particles, and production of nanophase Fe0 in amorphous rims of very fine irradiated lunar grains contributing to the observed variation of Is/FeO. 相似文献
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The structural state of an alkali feldspar is determined by the nature of the distribution of Al and Si in the tetrahedral sites of the feldspar structure. This state is a function of a number of genetic controls including temperature, cooling rate, deformation, crystal size, and several chemical factors. Together these controls constitute a genetic regime. Identification of the structures of detrital feldspars may enable recognition of genetic regimes and be useful in provenance interpretation and mineral province definition. A 2-peak method of X-ray diffraction (XRD) determination as a variant of an earlier proposed 3-peak method of structural state determination is used in this study. Total analytical time for each determination is about 50–55 min per grain. Results of structural state identification of 126 detrital feldspars from Holocene stream sands derived from volcanic, plutonic and metamorphic rocks are presented in order to illustrate the application and potential of the technique. Detrital feldspars from the metamorphic rocks are all maximum microcline; those from the plutons range from orthoclase to microcline depending on the age of the pluton, whereas those from the volcanic rocks are sanidines. 相似文献
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Peter J. ISAACSON Amit BASU SARBADHIKARI Carlé M. PIETERS Rachel L. KLIMA Takahiro HIROI Yang LIU Lawrence A. TAYLOR 《Meteoritics & planetary science》2011,46(2):228-251
The lunar rock and mineral characterization consortium (LRMCC) has conducted coordinated mineralogy/petrography/spectroscopy analyses of a suite of pristine lunar basalts. Four basalt slabs (two low‐Ti, two high‐Ti) and paired thin sections were analyzed. Thin sections were analyzed for mineralogy/petrography, while the slabs were used to prepare particulate separates of major mineral phases and bulk samples. Mineral separates and particulate bulk samples were crushed to controlled grain sizes and their reflectance spectra measured in the NASA RELAB at Brown University. The resulting data set provides an essential foundation for spectral mixing models, offers valuable endmember constraints for space weathering analyses, and represents critical new ground truth results for lunar science and exploration efforts. 相似文献
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BHASHA M MANKAD RASHMI SHARMA SUJIT BASU P K PAL 《Journal of Earth System Science》2012,121(1):251-262
Altimeter data have been assimilated in an ocean general circulation model using the water property conserving scheme. Two
runs of the model have been conducted for the year 2004. In one of the runs, altimeter data have been assimilated sequentially,
while in another run, assimilation has been suppressed. Assimilation has been restricted to the tropical Indian Ocean. An
assessment of the strength of the scheme has been carried out by comparing the sea surface temperature (SST), simulated in
the two runs, with in situ derived as well as remotely sensed observations of the same quantity. It has been found that the assimilation exhibits a
significant positive impact on the simulation of SST. The subsurface effect of the assimilation could be judged by comparing
the model simulated depth of the 20°C isotherm (hereafter referred to as D20), as a proxy of the thermocline depth, with the
same quantity estimated from ARGO observations. In this case also, the impact is noteworthy. Effect on the dynamics has been
judged by comparison of simulated surface current with observed current at a moored buoy location, and finally the impact
on model sea level forecast in a free run after assimilation has been quantified in a representative example. 相似文献
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Tidal variations in the Sundarbans Estuarine System, India 总被引：1，自引：0，他引：1
MEENAKSHI CHATTERJEE D SHANKAR G K SEN P SANYAL D SUNDAR G S MICHAEL ABHISEK CHATTERJEE P AMOL DEBABRATA MUKHERJEE K SUPRIT A MUKHERJEE V VIJITH SIDDHARTHA CHATTERJEE ANWESHA BASU MADHUMITA DAS SARANYA CHAKRABORTI ARAVIND KALLA SURJA KANTA MISRA SOUMYA MUKHOPADHYAY GOPAL MANDAL KANKAN SARKAR 《Journal of Earth System Science》2013,122(4):899-933
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Abstract— Soil 10084 is the only representative soil sample from Apollo 11 and arguably one of the purest mare soils in the Apollo collection. It was wet sieved in 1970 and dry sieved in 1971 with different results. Therefore, some doubt about its grain‐size distribution persists. We consider allocation inhomogeneity, if any, to be a minor cause for the discrepancy. Rather, the difference in methodology is likely to be the major cause for different results. We report the results of a new analysis of an allocation of 0.99 g using the contemporary method of wet sieving at Johnson Space Center; this method uses water instead of freon. Our results show that the mean grain size and sorting of the submillimeter fraction of soil 10084 are 4.28φ (= 51 μm) and 2.23φ (= 213 μm), respectively. A significant proportion (14.2%) of the soil is in the <10 μm size range, which contrasts to previous determinations of 6.4% and 9.8%, respectively. The newly determined grain‐size distribution is skewed towards the finest grain sizes. This result is more compatible with the high maturity of this soil than the results of previous determinations. 相似文献