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  • 1
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    Crystal/liquid partitioning of REE in basaltic systems Extreme fractionation of REE in olivine (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The calculation of partial coefficients for Nd, Sm, Gd, and Yb between olivine and synthetic basaltic melts using the percent level doping technique and microprobe analytical techniques is examined. The experimental and analytical procedures are described. The relationship between rare earth elements (REEs) concentrations and crystal margins caused by Rees X-rays from surrounding glass is discussed. Average olivine/liquid distribution coefficients for Nd, Sm, Gd, and Yb for mare and highlands basaltic melts are presented. The data reveal that the distribution coefficients for light REEs are lower than those obtained in previous studies, and the slope of the olivine/liquid distribution coefficient pattern is steeper; potential sources of error in the previous and present studies which could explain the differences in distribution coefficients and slope are investigated.
    Keywords: GEOPHYSICS
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 50; 69-79
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  • 2
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    Angrite LEW87051: Are the olivines pheno's or xeno's? A continuing story (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The achondrite LEW87051 is a porphyritic basalt consisting of large subhedral to euhedral zoned olivines in a finer-grained groundmass. The texture of this groundmass looks remarkably like a quenched melt. However, although the rock is clearly igneous, its exact origins and history are under dispute. From petrographic observations, Prinz felt that the large olivines were xenocrysts and that the zoning reflected interaction with an unrelated, CAI-enriched melt. McKay et al. was able to model the olivines as phenocrysts, whose zoning was the result of a parent melt that changed in composition as material crystallized, e.g., fractional crystallization in a closed system, and calculated a parent melt composition. Jurewicz and McKay compared the calculated parent melt composition with actual partial melts from CV and CM chondrites. They showed that the calculated melt was substantially different from equilibrium melts of these chondrites; however, the LEW87051 groundmass composition was similar to some of the low temperature partial melts, although slightly enriched in AN (or depleted in OL) components. This study presents the results of an independent petrologic look at other olivines in LEW87051 and the preliminary results of a quantitative model for the major zoning in these olivines as diffusive-exchange with an olivine-saturated, low temperature angritic melt.
    Keywords: GEOPHYSICS
    Type: Lunar and Planetary Inst., Twenty-Fourth Lunar and Planetary Science Conference. Part 2: G-M; p 737-738
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  • 3
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    Petrogenesis of KREEP (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Solid/liquid distribution coefficients (weight basis) were experimentally determined for a number of trace elements for olivine, orthopyroxene, plagioclase and ilmenite. Values of distribution coefficients were measured at 1200 C and a f sub O2 of 10 to the -13.0 power for liquids similar in composition to the olivine-opx-plagioclase peritectic in the pseudoternary system (Fe,Mg)2SiO4-CaAl2Si2O8-SiO2. Values were also measured at 1140 C and a f sub O2 of 10 to the -12.8 power for liquids similar in composition to high-Ti mare basalts. Major and trace element partitioning and relevant phase equilibria were used to investigate possible parent-daughter relationships between a number of highland samples and highly evolved KREEP-rich materials. Out of about 80 highlands samples tested, 33 were found to be possible parents to the KREEP-rich materials. The average composition of these samples is very similar to that of the Low-K Fra Mauro basalt (LKFM). A model is proposed to explain the production of LKFM-type material and more evolved members of the KREEP suite.
    Keywords: GEOPHYSICS
    Type: NASA-CR-148583
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  • 4
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    Charge balancing of trivalent trace elements in olivine and low-Ca pyroxene - A test using experimental partitioning data (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Charge-balancing substitution mechanisms are determined for the incorporation of the trivalent cations Al and Sc in low-Ca pyroxene and Al, Sc, Yb, and Cr in olivine. In low-Ca pyroxene, the substitution mechanism is determined by evaluating covariations of trivalent trace cations with Si, Mg, Fe, and Ca. In olivine, substitution mechanisms are determined by comparing the observed compositional dependence of partitioning to the compositional dependence theoretically expected for each substitution reaction. A realistic equilibrium constant is formulated for trace element exchanges between olivines, low-Ca pyroxenes, and melt, making possible improved modeling of the variations of trace element partitioning with temperature and phase composition.
    Keywords: GEOPHYSICS
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 53; 643-648
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  • 5
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    Temperature and composition dependencies of trace element partitioning - Olivine/melt and low-Ca pyroxene/melt (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: This paper presents a systematic thermodynamic analysis of the effects of temperature and composition on olivine/melt and low-Ca pyroxene/melt partitioning. Experiments were conducted in several synthetic basalts with a wide range of Fe/Mg, determining partition coefficients for Eu, Ca, Mn, Fe, Ni, Sm, Cd, Y, Yb, Sc, Al, Zr, and Ti and modeling accurately the changes in free energy for trace element exchange between crystal and melt as functions of the trace element size and charge. On the basis of this model, partition coefficients for olivine/melt and low-Ca pyroxene/melt can be predicted for a wide range of elements over a variety of basaltic bulk compositions and temperatures. Moreover, variations in partition coeffeicients during crystallization or melting can be modeled on the basis of changes in temperature and major element chemistry.
    Keywords: GEOPHYSICS
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 52; 539-553
    Format: text
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