Closing in on HED meteorite sources

Sykes, M. V.; Vilas, F.

doi:10.1186/bf03351706

Cited by 13 publications

(10 citation statements)

References 22 publications

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“…One of the efforts of the Dawn Science Team has been to investigate the geology of asteroid Vesta through geologic mapping. Geologic mapping attempts to decipher the evolution of a given body (e.g., Coradini et al, 2011;Greeley and Batson, 1990), to provide the context for the spectrally derived composition of the surface (e.g., De Sanctis et al, 2012a), and, in the case of Vesta, to understand the possible link with achondrite meteorites (e.g., McSween et al, 2011;Mayne et al, 2010;Sykes and Vilas, 2001). The first Dawn observations of Vesta's shape and morphology were reported by Jaumann et al (2012).…”

Section: Introductionmentioning

confidence: 99%

Geologic map of the northern hemisphere of Vesta based on Dawn Framing Camera (FC) images

Ruesch

Hiesinger

Blewett

et al. 2014

Icarus

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a b s t r a c tThe Dawn Framing Camera (FC) has imaged the northern hemisphere of the Asteroid (4) Vesta at high spatial resolution and coverage. This study represents the first investigation of the overall geology of the northern hemisphere (22-90°N, quadrangles Av-1, 2, 3, 4 and 5) using these unique Dawn mission observations. We have compiled a morphologic map and performed crater size-frequency distribution (CSFD) measurements to date the geologic units. The hemisphere is characterized by a heavily cratered surface with a few highly subdued basins up to $200 km in diameter. The most widespread unit is a plateau (cratered highland unit), similar to, although of lower elevation than the equatorial Vestalia Terra plateau. Large-scale troughs and ridges have regionally affected the surface. Between $180°E and $270°E, these tectonic features are well developed and related to the south pole Veneneia impact (Saturnalia Fossae trough unit), elsewhere on the hemisphere they are rare and subdued (Saturnalia Fossae cratered unit). In these pre-Rheasilvia units we observed an unexpectedly high frequency of impact craters up to $10 km in diameter, whose formation could in part be related to the Rheasilvia basin-forming event. The Rheasilvia impact has potentially affected the northern hemisphere also with S-N small-scale lineations, but without covering it with an ejecta blanket. Post-Rheasilvia impact craters are small (<60 km in diameter) and show a wide range of degradation states due to impact gardening and mass wasting processes. Where fresh, they display an ejecta blanket, bright rays and slope movements on walls. In places, crater rims have dark material ejecta and some crater floors are covered by ponded material interpreted as impact melt.

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Section: Introductionmentioning

confidence: 99%

Geologic map of the northern hemisphere of Vesta based on Dawn Framing Camera (FC) images

Ruesch

Hiesinger

Blewett

et al. 2014

Icarus

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“…Zappalá et al (1995) concluded that Vesta possesses a dynamic family of ~240 small asteroids, which are closely associated with it physically and which may have derived from a large collision with Vesta. This Vesta family may have been ejected from one of these large craters (Sykes and Vilas 2001). In addition, observers have identified 18 Vestoids, which are small (~4-10 km) asteroids with Vesta-like spectra and the orbits of which form a bridge connecting Vesta with the ν 6 resonance and the 3:1 Kirkwood gap (Binzel and Xu 1993).…”

Section: Impact-produced Agesmentioning

confidence: 99%

“…Gravitational perturbations by Jupiter from the ν 6 resonance and the 3:1 Kirkwood gap are thought to be "gates" through which objects pass on their way to Earth (Wisdom 1985;Binzel and Xu 1993;Wetherill 1985). Thus, eucrites in our collections likely derived originally from one or more large impacts on Vesta (or a similar body now disrupted) and were brought to Earth by further collisions on one of these smaller, secondary asteroids (Sykes and Vilas 2001).…”

Section: Impact-produced Agesmentioning

confidence: 99%

“…Several quite large impact craters apparently exist on Vesta (Thomas et al 1997;Gaffey 1997). These may have been the source of the relatively large asteroidal family dynamically associated with Vesta and those asteroids with eucrite-like spectra, which are distributed in space between the ν 6 resonance and the 3:1 Kirkwood gap, likely making them direct parent objects for meteorites that fall on Earth (Zappalá et al 1995;Binzel and Xu 1993;Sykes and Vilas 2001).…”

Section: Vesta's Thermal Historymentioning

confidence: 99%

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³⁹Ar‐⁴⁰Ar ages of eucrites and thermal history of asteroid 4 Vesta

Bogard

Garrison

2003

Meteorit & Planetary Scien

109

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available online at http://meteoritics.org 669 Abstract-Eucrite meteorites are igneous rocks that derived from a large asteroid, probably 4 Vesta. Past studies have shown that after most eucrites formed, they underwent metamorphism in temperatures up to ≥800°C. Much later, many were brecciated and heated by large impacts into the parent body surface. The less common basaltic, unbrecciated eucrites also formed near the surface but, presumably, escaped later brecciation, while the cumulate eucrites formed at depths where metamorphism may have persisted for a considerable period. To further understand the complex HED parent body thermal history, we determined new 39 Ar-40 Ar ages for 9 eucrites classified as basaltic but unbrecciated, 6 eucrites classified as cumulate, and several basaltic-brecciated eucrites. Precise Ar-Ar ages of 2 cumulate eucrites (Moama and EET 87520) and 4 unbrecciated eucrites give a tight cluster at 4.48 ± 0.02 Gyr (not including any uncertainties in the flux monitor age). Ar-Ar ages of 6 additional unbrecciated eucrites are consistent with this age within their relatively larger age uncertainties. By contrast, available literature data on Pb-Pb isochron ages of 4 cumulate eucrites and 1 unbrecciated eucrite vary over 4.4-4.515 Gyr, and 147 Sm-143 Nd isochron ages of 4 cumulate and 3 unbrecciated eucrites vary over 4.41-4.55 Gyr. Similar Ar-Ar ages for cumulate and unbrecciated eucrites imply that cumulate eucrites do not have a younger formation age than basaltic eucrites, as was previously proposed. We suggest that these cumulate and unbrecciated eucrites resided at a depth where parent body temperatures were sufficiently high to cause the K-Ar and some other chronometers to remain as open diffusion systems. From the strong clustering of Ar-Ar ages at ~4.48 Gyr, we propose that these meteorites were excavated from depth in a single large impact event ~4.48 Gyr ago, which quickly cooled the samples and started the K-Ar chronometer. A large (~460 km) crater postulated to exist on Vesta may be the source of these eucrites and of many smaller asteroids thought to be spectrally or physically associated with Vesta. Some Pb-Pb and Sm-Nd ages of cumulate and unbrecciated eucrites are consistent with the Ar-Ar age of 4.48 Gyr, and the few older Pb-Pb and Sm-Nd ages may reflect an isotopic closure before the large cratering event. One cumulate eucrite gives an Ar-Ar age of 4.25 Gyr; 3 additional cumulate eucrites give Ar-Ar ages of 3.4-3.7 Gyr; and 2 unbrecciated eucrites give Ar-Ar ages of ~3.55 Gyr. We attribute these younger ages to a later impact heating. Furthermore, the Ar-Ar impact-reset ages of several brecciated eucrites and eucritic clasts in howardites fall within the range of 3.5-4.

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“…Recent measurements of four Vesta and vestoids reflectance spectra showed an absorption feature near 505 nm corresponding to Fe 2+ in six-fold coordination that is attributed to Ca in pyroxene [6,7]. This absorption feature is also seen in the spectra of eucrite and howardite but not in glassy diogenite [8]. Thus although pyroxene is the main mineral constituent of all three classes (howardite, eucrite and diogenite) of meteorites, there are minor differences in the finer structure of pyroxene in these.…”

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confidence: 90%

Preferential occupation of pyroxene sites by iron in diogenite meteorites

Verma¹,

Tewari

Paliwal³

et al. 2008

Hyperfine Interact

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Three diogenite meteorites ALHA77256-121, Tatahounie and Bilanga are studied using Mössbauer spectroscopy to look at the iron occupancy in the two inequivalent pyroxene sites. Though the three meteorites belong to three different conditions, one is an Antarctica find, one is 75 years old fall and one is a recent fall, the iron occupancy in pyroxene sites is very similar. Fe 2+ occupies only the less distorted site and hence a single sharp doublet is observed in the Mössbauer spectra of all these samples. In contrast eucrites show a distribution of iron ions in the two sites of pyroxenes.

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Closing in on HED meteorite sources

Cited by 13 publications

References 22 publications

Geologic map of the northern hemisphere of Vesta based on Dawn Framing Camera (FC) images

Geologic map of the northern hemisphere of Vesta based on Dawn Framing Camera (FC) images

³⁹Ar‐⁴⁰Ar ages of eucrites and thermal history of asteroid 4 Vesta

Preferential occupation of pyroxene sites by iron in diogenite meteorites

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Closing in on HED meteorite sources

Cited by 13 publications

References 22 publications

Geologic map of the northern hemisphere of Vesta based on Dawn Framing Camera (FC) images

Geologic map of the northern hemisphere of Vesta based on Dawn Framing Camera (FC) images

39Ar‐40Ar ages of eucrites and thermal history of asteroid 4 Vesta

Preferential occupation of pyroxene sites by iron in diogenite meteorites

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³⁹Ar‐⁴⁰Ar ages of eucrites and thermal history of asteroid 4 Vesta