Chondrule‐like objects and brown glasses in howardites

Olsen, Edward; Fredriksson, K.; Rajan, S.; Noonan, A. F.

doi:10.1111/j.1945-5100.1990.tb00996.x

Cited by 35 publications

(16 citation statements)

References 22 publications

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“…Fine-grained porphyritic or microporphyritic clasts composed of pyroxene phenocrysts or microphenocrysts in holocrystalline or variolitic groundmass of acicular plagioclase and pyroxene have been described in few howardites (Dymek et al, 1976;Mittlefehldt and Lindstrom, 1997), but these seem likely to be impact-melt clasts of howarditic composition (Mittlefehldt and Lindstrom, 1997). Texturally and mineralogically, they are similar to microporphyritic glassy spherules and fragments (Barrat et al, 2009a;Olsen et al, 1990;Singerling et al, 2013). Howardite Y-7308 contains olivine-orthopyroxene clasts with variable amounts of plagioclase, chromite and high-Ca clinopyroxene (Ikeda and Takeda, 1985).…”

Section: Hed Polymict Brecciasmentioning

confidence: 96%

“…Warren et al (2009) used the abundance of glass particles, especially brown, turbid glass, as one indicator that a howardite might be regolithic. Glassy particles may contain microphenocrysts of olivine and/or low-Ca pyroxene (Barrat et al, 2009a;Bunch, 1975;Hewins and Klein, 1978;Labotka and Papike, 1980;Mittlefehldt and Lindstrom, 1998;Olsen et al, 1990;Singerling et al, 2013). Most glassy particles in HED polymict breccias have petrologic characteristics and compositions indicating that they are impact-melt particles of the vestan regolith (e.g., Olsen et al, 1990;Singerling et al, 2013).…”

Section: Hed Polymict Brecciasmentioning

confidence: 97%

“…Glassy spheres and irregularly shaped particles are commonly found in howardites and can be composed of glass sensu stricto or devitrified glass (e.g., Barrat et al, 2009a;Bunch, 1975;Hewins and Klein, 1978;Labotka and Papike, 1980;Olsen et al, 1990). Warren et al (2009) used the abundance of glass particles, especially brown, turbid glass, as one indicator that a howardite might be regolithic.…”

Section: Hed Polymict Brecciasmentioning

confidence: 98%

“…Glassy particles may contain microphenocrysts of olivine and/or low-Ca pyroxene (Barrat et al, 2009a;Bunch, 1975;Hewins and Klein, 1978;Labotka and Papike, 1980;Mittlefehldt and Lindstrom, 1998;Olsen et al, 1990;Singerling et al, 2013). Most glassy particles in HED polymict breccias have petrologic characteristics and compositions indicating that they are impact-melt particles of the vestan regolith (e.g., Olsen et al, 1990;Singerling et al, 2013). However, some have unusual compositions suggestive of formation from specific lithologic components, such as evolved mesostasis (Singerling et al, 2013), or distinctly different lithologic terrains (Barrat et al, 2009a,b).…”

Section: Hed Polymict Brecciasmentioning

confidence: 98%

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Asteroid (4) Vesta: I. The howardite-eucrite-diogenite (HED) clan of meteorites

2015

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Section: Hed Polymict Brecciasmentioning

confidence: 96%

Section: Hed Polymict Brecciasmentioning

confidence: 97%

Section: Hed Polymict Brecciasmentioning

confidence: 98%

Section: Hed Polymict Brecciasmentioning

confidence: 98%

See 2 more Smart Citations

Asteroid (4) Vesta: I. The howardite-eucrite-diogenite (HED) clan of meteorites

2015

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“…Many HED breccias, including most, and possibly all, howardites but no eucrites or diogenites, feature glass spherules and very finegrained "dark-matrix '' regions (Labotka and Papike, 1980;Fuhrman and Papike, 1981;Ikeda and Takeda, 1984;Olsen et al, 1990) that, by analogy with lunar regolith samples, indicate presence of materials derived from the impact-"gardened" outer few meters of the parent body. Four howardites also show enrichments in solar-wind derived noble gases, which is a firm indication of regolith origin (Fig.…”

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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HED Meteorites and Their Relationship to the Geology of Vesta and the Dawn Mission

McSween

Mittlefehldt

Beck

et al. 2010

The Dawn Mission to Minor Planets 4 Vesta and 1 Ceres

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Howardite-e ucrite-diogenite (HED) meteorites, thought to be derived from 4 Vesta, provide the best sampling available for any differentiated asteroid. However, deviations in oxygen isotopic composition from a common mass-fractionation line suggest that a few eucrite-like meteorites are from other bodies, or that Vesta was not completely homogenized during differentiation. The petrology and geochemistry of HEDs provide insights into igneous processes that produced a crust composed of basalts, gabbros, and ultramafic cumulate rocks. Although most HED magmas were fractionated, it is unresolved whether some cucrites may have been primary melts. The geochemistry of HEDs indicates that bulk Vesta is depleted in volatile elements and is relatively reduced, but has chondritic refractory element abundances. The compositions of HEDs may favor a magma ocean model, but inconislencies remain. Geochronology indicates that Vesta accreted and differentiated within the first several million years of solar system history, that magmatism continued over a span of . . . . . \0 Myr, and that its thermal history extended for perhaps 100 Myr. The protracted cooling history is probabl y responsible for thermal metamorphism of most HEDs. Impact chronology indicates that Vesta ex perienced many significant collisions, including during the late heavy bombardment. The age of the huge south pole crater is controversial, but it probably ejected Vestoids and many HEDs. Continued impacts produced a regolith composed of eu-(me and diogenite fragments containing only minor exotic materials. HED meteorites serve ib ground truth for orbital spectroscopic and chemical analyses by the Dawn spacecraft, and H,( \1cSween Jr. (C8J). A

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Chondrule‐like objects and brown glasses in howardites

Cited by 35 publications

References 22 publications

Asteroid (4) Vesta: I. The howardite-eucrite-diogenite (HED) clan of meteorites

Asteroid (4) Vesta: I. The howardite-eucrite-diogenite (HED) clan of meteorites

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

HED Meteorites and Their Relationship to the Geology of Vesta and the Dawn Mission

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