Ion microprobe study of the Pomozdino and Peramiho eucrites

Hsu, Weibiao; Crozaz, G.

doi:10.1111/j.1945-5100.1997.tb01265.x

Cited by 3 publications

(2 citation statements)

References 18 publications

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“…Furthermore, we observe that the percent deviation of the Fe bulk abundance for Pomozdino is 15% in line with the cumulate eucrites. Therefore, we concur with Hsu and Crozaz (1997), Warren and Jerde (1988) and Warren (1997) that Pomozdino most probably has some type of cumulate component incorporated into it.…”

Section: Mineralogical Compositionsupporting

confidence: 91%

Survey and evaluation of eucrite bulk compositions

Kitts

Lodders

1998

Meteorit & Planetary Scien

111

101

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Abstract-The purpose of this survey is to establish reference bulk elemental abundances for the eucrites and thereby provide the basis to test core formation models as well as partial melting, fractional crystallization and magma ocean theories for the eucrite parent body. In order to evaluate bulk elemental abundances for the eucrites, 296 peer-reviewed articles, monographs, theses or books and 143 abstracts dating from 1938 to 1997 were surveyed. Of the 10 1 eucrites having at least one set of elemental abundance analyses reported in the literature, 20 were selected for in-depth examination. The selection criteria of our sample were based on the total number of analyses available for a given eucrite and the total number of elements for which data exist. The mean bulk elemental abundance, la standard deviation, and the percent deviation were calculated for each element in a given eucrite. In order to evaluate the quality of the mean abundances, the elements were then grouped according to availability of data and percent deviations. Possible reasons for the different deviations in the different groups are briefly discussed. From the major element abundances, the normative (CIPW) composition, the molar compositions of pyroxene, olivine and plagioclase, and the bulk densities were calculated and compared to petrographic observations. The calculated norms for the noncumulates agree well with the observations while the norms for the cumulates do not. Possible reasons for this are discussed. Unfortunately, analyses of many elements are poorly represented in the literature and many bulk analyses suffer from unacceptable levels of uncertainty. Therefore, future work requires bulk elemental analyses for some of the more poorly characterized elements in eucrites, especially those of key elements used for planetary modeling.

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Section: Mineralogical Compositionsupporting

confidence: 91%

Survey and evaluation of eucrite bulk compositions

Kitts

Lodders

1998

Meteorit & Planetary Scien

111

101

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“…The uniquely low-mg# Yamato "b" is probably genomict (Le., mildly polymict, see text). The unusual eucrite Pomozdino has been suggested to be a partial cumulate (Warren et ul., 1990) or an impact melt product (Hsu and Crozaz, 1996); it is certainly not a typical noncumulate eucrite. Also shown are approximate mg# for parent melts of definite cumulate eucrites, estimated using the method of Warren and Kallemeyn (1992b) (i.e., based on bulk-rock mg# and concentration of Sm, an incompatible element used for constraining the cumulate's "Crapped liquid" content), where the parent melt's Sm content is assumed to be roughly comparable to the average for the two lowest-mg# eucrites, Nuevo Laredo and Lakangaon.…”

Section: Constraints On the Diogenitel (Diogenite + Eucrite) Ratio Ofmentioning

confidence: 99%

Magnesium oxide‐iron oxide mass balance constraints and a more detailed model for the relationship between eucrites and diogenites

Warren

1997

Meteorit & Planetary Scien

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Abstract-According to a currently popular model for petrogenesis on the howardite, eucrite, and diogenite (HED) parent asteroid, the diogenites are not comagmatic with most eucrites but instead formed in separate orthopyroxenite-dominated plutons. This model can be tested for consistency with mass balance for MgO and FeO, assuming the overall diogenite/(diogenite + eucrite) ratio, d, of the parent asteroid is at least comparable to the average d for the eucrite + diogenite dominated howardite regolith breccias. Average mg# (=MgO/ [MgO + FeO]) is much lower for eucrites, especially noncumulate eucrites, than for diogenites. Unless the diogenite parent magmas eventually produced a large proportion of low-mg# residual basalt and gabbro (RBG), the implied initial magma's mg# is vastly higher than that of any noncumulate eucrite. Starting from a source previously depleted by putative primary eucrite genesis, melt mg# can be estimated as a finction of the exchange reaction KD and degree of melting. Using several very conservative assumptions (e.g., assuming that the total [MgO + FeO] concentration is nearly the same in the nascent melt as in the residual solids), the degree of melting required to yield a melt with mg# high enough to satisfy mass balance, without implying an RBG component that accounts for >50% of all eucrites, is an implausibly high 60-80 wt?!.The separate orthopyroxenitic plutons (SOP) model also seems inconsistent with the uniform density of melts across the diogenite-eucrite compositional spectrum (2.77-2.82 g/cm3), which implies that diogenitic magmas should have been as capable as eucrites of extruding to form lavas. This difficulty cannot be reduced by simply assuming that later-formed magmas were systematically both more plutonic and more MgOrich than earlier ones, because the plutonic cumulate eucrites equilibrated with melts systematically lower in mg# than noncumulate eucrites. Conceivably, the bulk mg# of the asteroid's silicate system was increased between primary-melt eucrite genesis and SOP diogenite genesis by graphite-fieled reduction of FeO. However, the graphite oxidation process generates a huge proportion of gas, which would have enhanced the buoyancy of the nascent diogenite-parent magmas, thus exacerbating the difficulty of achieving the implied high degrees of partial melting.To avoid these difficulties but still form most eucrites as rapidly cooled extrusives, I propose the NERD (noncumulate eucrites as extruded residua of diogenites) model. In this model, the diogenites form as early cumulates from a large magma system (probably a global "magma ocean") that yields a large proportion of eucritic melt as residuum. This residual melt zone undergoes relatively little crystallization during a period when it is episodically tapped to produce extrusions, dikes and sills of rapidly cooled noncumulate eucrites. Slight (-5-10%) porosity in the nascent eucritic crust keeps it marginally buoyant over the residual melt zone. The common thermal metamorphism of noncumulate eucrites results f...

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