Relative chronology of crust formation on asteroid Vesta: Insights from the geochemistry of diogenites

Barrat, Jean‐Alix; Yamaguchi, A.; Zanda, B.; Bollinger, Claire; Bohn, Marcel

doi:10.1016/j.gca.2010.07.028

Cited by 96 publications

(163 citation statements)

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“…Ba and Sr abundances and sometimes anomalous REE distributions (e.g., Barrat et al, 2010). Therefore, 210 only two mildly weathered Saharan ureilites were selected for this study.…”

Section: Explanation 181mentioning

confidence: 99%

“…Only these data and the P abundances of the unleached fractions will be 207 used in the following sections and drawn in the various figures. In contrast with Antarctic samples, the hot 208 desert finds contained secondary phases such as barite, which are not easily leachable and account for high 209Ba and Sr abundances and sometimes anomalous REE distributions (e.g., Barrat et al, 2010). Therefore, 210 only two mildly weathered Saharan ureilites were selected for this study.…”

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confidence: 99%

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Partial melting of a C-rich asteroid: Lithophile trace elements in ureilites

Barrat

Jambon

Yamaguchi

et al. 2016

Geochimica et Cosmochimica Acta

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29Ureilites are among the most common achondrites and are widely believed to sample the mantle of a 30 single, now-disrupted, C-rich body. We analyzed 17 ureilite samples, mostly Antarctic finds, and determined 31 their incompatible trace element abundances. In order to remove or reduce the terrestrial contamination, 32 which is marked among Antarctic ureilites by light-REE enrichment, we leached the powdered samples with 33 nitric acid. The residues display consistent abundances, which strongly resemble those of the pristine rocks. 34All the analyzed samples display light-REE depletions, negative Eu anomalies, low (Sr/Eu*) n , and (Zr/Eu*) n 35 ratios which are correlated. Two groups of ureilites (groups A and B) are defined. Compared to group A, 36 group B ureilites, which are the less numerous, tend to be richer in heavy REEs, more light-REE depleted, 37 and display among the deepest Eu anomalies. In addition, olivine cores in group B ureilites tend to be more 38 forsteritic (Mg# = 81.9-95.2) than in group A ureilites (Mg# = 74.7-86.1). Incompatible trace element 39 systematics supports the view that ureilites are mantle restites. REE modelling suggests that their precursors 40were rather REE-rich (ca. 1.8-2 x CI) and contained a phosphate phase, possibly merrillite. The REE 41 abundances in ureilites can be explained if at least two distinct types of magmas were removed successively 42 from their precursors: aluminous and alkali-rich melts as exemplified by the Almahata Sitta trachyandesite 43 (ALM-A), and Al and alkali-poor melts produced after the exhaustion of plagioclase from the source. Partial 44 melting was near fractional (group B ureilites, which are probably among the least residual samples) to 45 dynamic with melt porosities that did not exceed a couple of percent (group A ureilites). The ureilite parent 46 body (UPB) was almost certainly covered by a crust formed chiefly from the extrusion products of the 47 aluminous and alkali-rich magmas. It is currently uncertain whether the Al and alkali-poor melts produced 48 during the second phase of melting reached the surface of the body. The fact that initial silicate melting of 49 ureilitic precursors would have produced relatively low density liquids capable of forming an external crust 50 to the UPB casts doubt on models that invoke chondritic outer layers to achondritic asteroids. 51 52 1. Introduction 53 54 55The early history of the Solar System was marked by the accretion of numerous asteroid-sized bodies 56 (large asteroids and embryos). Many of them underwent rapid internal heating, leading to melting and 57 subsequent differentiation. Among the most significant issues for understanding the differentiation of rocky 58 bodies are the exact processes of melting, the compositions of the generated magmas and how these were 59 then segregated from their sources. Melt migration may have involved ascent to the surface to form a crust, 60 or alternatively escape to space by explosive volcanism. It has recently been argued that partial melting...

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“…Ba and Sr abundances and sometimes anomalous REE distributions (e.g., Barrat et al, 2010). Therefore, 210 only two mildly weathered Saharan ureilites were selected for this study.…”

Section: Explanation 181mentioning

confidence: 99%

mentioning

confidence: 99%

Partial melting of a C-rich asteroid: Lithophile trace elements in ureilites

Barrat

Jambon

Yamaguchi

et al. 2016

Geochimica et Cosmochimica Acta

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“…Specifically, they predicted shallow dikes with widths of $1 m and vertical extents of <10 km and/or deep dikes with thicknesses 3 m and lateral extents 30 km. In addition, Barrat et al (2010), who performed a detailed study of the trace-element chemistry of diogenites which suggests that their petrogenesis is more complex than that of simple early crystallization products, proposed that Vesta's diogenites possibly formed as later-stage plutons injected into a eucrite crust. More recently, Keil and Wilson (2012) suggested that there may be many sill-like intrusions at the base of Vesta's lithosphere.…”

Section: Formation Of Brumalia Tholusmentioning

confidence: 99%

“…However, it is possible that the Albalonga fault pre-dates the end of Vesta volcanism, and thus that the material that injected the fault could have been sourced by either the magma plume theorized by Raymond et al (2013) to have formed the Vestalia Terra plateau, from the sill-like intrusions Keil and Wilson (2012) projected to be at the base of the vestan lithosphere or from one of the diogenitic intrusions into eucritic crust predicted by Barrat et al (2010). While the orientation of Albalonga Catena and the other two Vestalia Terra pit crater chains is roughly consistent with that of the equatorial troughs, it is possible that their underlying faults pre-date the Rheasilvia impact.…”

Section: Formation Of Brumalia Tholusmentioning

confidence: 99%

“…The fact that diogenites are coarse grained and of high Mg# (molar Mg/(Mg + Fe)) when compared to basaltic eucrites led to the idea that the crust of the parent body may have a simple layered structure possibly formed during cooling of a global magma ocean, with surface basaltic eucrites overlying deeper diogenites (Takeda, 1979). However, detailed study of the trace-element chemistry of diogenites suggests that their petrogenesis is more complex than that of simple early crystallization products and it has been proposed that they are possibly laterstage plutons injected into the eucrite crust (Barrat et al, 2010). Distinguishing between these two very different proposed crustal structures is thus vital toward understanding Vesta's history.…”

Section: Introductionmentioning

confidence: 99%

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The unique geomorphology and physical properties of the Vestalia Terra plateau

Buczkowski¹,

Wyrick²,

Toplis³

et al. 2014

Icarus

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a b s t r a c tWe produced a geologic map of the Av-9 Numisia quadrangle of asteroid Vesta using Dawn spacecraft data to serve as a tool to understand the geologic relations of surface features in this region. These features include the plateau Vestalia Terra, a hill named Brumalia Tholus, and an unusual ''dark ribbon'' material crossing the majority of the map area. Stratigraphic relations suggest that Vestalia Terra is one of the oldest features on Vesta, despite a model crater age date similar to that of much of the surface of the asteroid. Cornelia, Numisia and Drusilla craters reveal bright and dark material in their walls, and both Cornelia and Numisia have smooth and pitted terrains on their floors suggestive of the release of volatiles during or shortly after the impacts that formed these craters. Cornelia, Fabia and Teia craters have extensive bright ejecta lobes. While diogenitic material has been identified in association with the bright Teia and Fabia ejecta, hydroxyl has been detected in the dark material within Cornelia, Numisia and Drusilla. Three large pit crater chains appear in the map area, with an orientation similar to the equatorial troughs that cut the majority of Vesta. Analysis of these features has led to several interpretations of the geological history of the region. Vestalia Terra appears to be mechanically stronger than the rest of Vesta. Brumalia Tholus may be the surface representation of a dike-fed laccolith. The dark ribbon feature is proposed to represent a long-runout ejecta flow from Drusilla crater.

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Small fresh impact craters on asteroid 4 Vesta: A compositional and geological fingerprint

et al. 2014

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Small morphologically fresh impact craters (<10 km in diameter) on Vesta's surface with a photometrically distinct ejecta blanket are expected to represent fresh surface material and thus provide the opportunity to study the composition of the unweathered surface. Dawn-Framing Camera and Visual and Infrared Spectrometer (VIR) data reveal impact craters with bright, dark, and mixed, i.e., partly bright and dark, ejecta existing on Vesta's surface, which not only differ in the visible albedo from their surroundings but also in their composition. Differences in the composition are related to the visible albedo and/or the geographic location of the impact craters. Bright ejecta, only seen in the southern Vestan hemisphere, are dominated by howardite/eucrite-like material as expected for Vesta's upper crust. Dark ejecta associated with dark impact craters are dominated by a strongly absorbing, spectrally neutral compound, supporting an origin from carbon-rich impactors. Few impact craters of intermediate albedo in Vesta's southern hemisphere contain material resembling diogenites, which are expected to exist in the deeper parts of Vesta's interior. The geological settings suggest that the diogenite-like material represents a part of a layer of diogenitic material surrounding the Rheasilvia basin or local concentrations of diogenitic material as part of the ejecta excavated during the latter stage of the Rheasilvia impact event. The spectral differences between eucrite-and diogenite-dominated materials also could be verified due to spin-forbidden absorptions in the visible spectral range, which are known from laboratory spectra of pyroxenes, but, which have been identified in the VIR spectra of Vesta for the first time.

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Relative chronology of crust formation on asteroid Vesta: Insights from the geochemistry of diogenites

Cited by 96 publications

References 49 publications

Partial melting of a C-rich asteroid: Lithophile trace elements in ureilites

Partial melting of a C-rich asteroid: Lithophile trace elements in ureilites

The unique geomorphology and physical properties of the Vestalia Terra plateau

Small fresh impact craters on asteroid 4 Vesta: A compositional and geological fingerprint

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