Observations of impact-induced molten metal-silicate partitioning

Rowan, Linda; Ahrens, Thomas J.

doi:10.1016/0012-821x(94)90052-3

Cited by 19 publications

(15 citation statements)

References 27 publications

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“…Those identified in Stardust aerogel are also believed to result from impacts, although they are instead believed to have formed as a result of the particle collection method (i.e., via impact) rather than as a result of impacts on the parent body. Indeed, Fe‐silicide beads of a range of Si‐contents have previously been identified in melts produced during shock experiments: Badjukov and Petrova () identified Fe‐silicides in melts produced by a range of silicate targets shocked in cylindrical steel containers surrounded by high explosive and Rowan and Ahrens () observed them in the experimental impact melts produced in samples of midocean ridge basalts. The Fe‐silicide phases are thought to have formed as a result of melting and mixing of Fe and Si (from the materials involved) under reducing conditions.…”

Section: Resultsmentioning

confidence: 99%

The survivability of phyllosilicates and carbonates impacting Stardust Al foils: Facilitating the search for cometary water

Wozniakiewicz

Ishii

Kearsley

et al. 2015

Meteorit & Planetary Scien

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Abstract-Comet 81P/Wild 2 samples returned by NASA's Stardust mission provide an unequalled opportunity to study the contents of, and hence conditions and processes operating on, comets. They can potentially validate contentious interpretations of cometary infrared spectra and in situ mass spectrometry data: specifically the identification of phyllosilicates and carbonates. However, Wild 2 dust was collected via impact into capture media at~6 km s À1 , leading to uncertainty as to whether these minerals were captured intact, and, if subjected to alteration, whether they remain recognizable. We simulated Stardust Al foil capture conditions using a two-stage light-gas gun, and directly compared transmission electron microscope analyses of pre-and postimpact samples to investigate survivability of lizardite and cronstedtite (phyllosilicates) and calcite (carbonate). We find the phyllosilicates do not survive impact as intact crystalline materials but as moderately to highly vesiculated amorphous residues lining resultant impact craters, whose bulk cation to Si ratios remain close to that of the impacting grain. Closer inspection reveals variation in these elements on a submicron scale, where impact-induced melting accompanied by reducing conditions (due to the production of oxygen scavenging molten Al from the target foils) has resulted in the production of native silicon and Fe-and Fe-Si-rich phases. In contrast, large areas of crystalline calcite are preserved within the calcite residue, with smaller regions of vesiculated, Al-bearing calcic glass. Unambiguous identification of calcite impactors on Stardust Al foil is therefore possible, while phyllosilicate impactors may be inferred from vesiculated residues with appropriate bulk cation to Si ratios. Finally, we demonstrate that the characteristic textures and elemental distributions identifying phyllosilicates and carbonates by transmission electron microscopy can also be observed by state-of-the-art scanning electron microscopy providing rapid, nondestructive initial mineral identifications in Stardust residues.

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Section: Resultsmentioning

confidence: 99%

The survivability of phyllosilicates and carbonates impacting Stardust Al foils: Facilitating the search for cometary water

Wozniakiewicz

Ishii

Kearsley

et al. 2015

Meteorit & Planetary Scien

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“…Significant FeO reduction (ranging up to almost complete loss of FeO at the highest shock pressures) has been observed in experimentally shocked basalt liquids (Rowan and Ahrens 1994). Thermal decomposition of FeO and other volatile species would be expected to occur as a result of the transient high temperatures involved in a shock event (Wasson et al 2006), especially if hot FeO-bearing liquids were decompressed and exposed to space, where they would be expected to boil.…”

Section: Implications For the Iva Parent Bodymentioning

confidence: 99%

Differentiation and evolution of the IVA meteorite parent body: Clues from pyroxene geochemistry in the Steinbach stony-iron meteorite

Ruzicka

Hutson

2006

Meteoritics &Amp; Planetary Science

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Abstract-We analyzed the Steinbach IVA stony-iron meteorite using scanning electron microscopy (SEM), electron microprobe analysis (EMPA), laser ablation inductively-coupled-plasma mass spectroscopy (LA-ICP-MS), and modeling techniques. Different and sometimes adjacent low-Ca pyroxene grains have distinct compositions and evidently crystallized at different stages in a chemically evolving system prior to the solidification of metal and troilite. Early crystallizing pyroxene shows evidence for disequilibrium and formation under conditions of rapid cooling, producing clinobronzite and type 1 pyroxene rich in troilite and other inclusions. Subsequently, type 2 pyroxene crystallized over an extensive fractionation interval. Steinbach probably formed as a cumulate produced by extensive crystal fractionation (~60-70% fractional crystallization) from a high-temperature (~1450-1490 °C) silicate-metallic magma. The inferred composition of the precursor magma is best modeled as having formed by ≥30-50% silicate partial melting of a chondritic protolith. If this protolith was similar to an LL chondrite (as implied by O-isotopic data), then olivine must have separated from the partial melt, and a substantial amount (~53-56%) of FeO must have been reduced in the silicate magma. A model of simultaneous endogenic heating and collisional disruption appears best able to explain the data for Steinbach and other IVA meteorites. Impact disruption occurred while the parent body was substantially molten, causing liquids to separate from solids and oxygen-bearing gas to vent to space, leading to a molten metal-rich body that was smaller than the original parent body and that solidified from the outside in. This model can simultaneously explain the characteristics of both stony-iron and iron IVA meteorites, including the apparent correlation between metal composition and metallographic cooling rate observed for metal.

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“…We therefore suggest that the anomalies were produced at high temperature by the presence of a reducing gas that was quickly lost, under disequilibrium conditions. Extreme but short-lived reduction has been documented for soils affected by lightning strikes (Essene and Fisher 1986) and for experimentally shocked basaltic melts (Rowan and Ahrens 1994). A possible reduction mechanism for Sombrerete is the formation of a high-C/O gas by rapid heating of C-bearing target materials (e.g., graphite, organic compounds or carbides) or by the degassing of oxygen during hypervelocity impact.…”

Section: Origin Of Yb and Sm Anomaliesmentioning

confidence: 99%

Petrology of silicate inclusions in the Sombrerete ungrouped iron meteorite: Implications for the origins of IIE‐type silicate‐bearing irons

Ruzicka

Hutson

Floss

2006

Meteorit & Planetary Scien

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Abstract-The petrography and mineral and bulk chemistries of silicate inclusions in Sombrerete, an ungrouped iron that is one of the most phosphate-rich meteorites known, was studied using optical, scanning electron microscopy (SEM), electron microprobe analysis (EMPA), and secondary ion mass spectrometry (SIMS) techniques. Inclusions contain variable proportions of alkalic siliceous glass (~69 vol% of inclusions on average), aluminous orthopyroxene (~9%, Wo 1−4 Fs 25-35 , up to ~3 wt% Al), plagioclase (~8%, mainly An 70-92 ), Cl-apatite (~7%), chromite (~4%), yagiite (~1%), phosphaterich segregations (~1%), ilmenite, and merrillite. Ytterbium and Sm anomalies are sometimes present in various phases (positive anomalies for phosphates, negative for glass and orthopyroxene), which possibly reflect phosphate-melt-gas partitioning under transient, reducing conditions at high temperatures. Phosphate-rich segregations and different alkalic glasses (K-rich and Na-rich) formed by two types of liquid immiscibility. Yagiite, a K-Mg silicate previously found in the Colomera (IIE) iron, appears to have formed as a late-stage crystallization product, possibly aided by Na-K liquid unmixing. Trace-element phase compositions reflect fractional crystallization of a single liquid composition that originated by low-degree (~4-8%) equilibrium partial melting of a chondritic precursor. Compositional differences between inclusions appear to have originated as a result of a "filter-press differentiation" process, in which liquidus crystals of Cl-apatite and orthopyroxene were less able than silicate melt to flow through the metallic host between inclusions. This process enabled a phosphoran basaltic andesite precursor liquid to differentiate within the metallic host, yielding a dacite composition for some inclusions. Solidification was relatively rapid, but not so fast as to prevent flow and immiscibility phenomena. Sombrerete originated near a cooling surface in the parent body during rapid, probably impact-induced, mixing of metallic and silicate liquids. We suggest that Sombrerete formed when a planetesimal undergoing endogenic differentiation was collisionally disrupted, possibly in a breakup and reassembly event. Simultaneous endogenic heating and impact processes may have widely affected silicate-bearing irons and other solar system matter.

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Observations of impact-induced molten metal-silicate partitioning

Cited by 19 publications

References 27 publications

The survivability of phyllosilicates and carbonates impacting Stardust Al foils: Facilitating the search for cometary water

The survivability of phyllosilicates and carbonates impacting Stardust Al foils: Facilitating the search for cometary water

Differentiation and evolution of the IVA meteorite parent body: Clues from pyroxene geochemistry in the Steinbach stony-iron meteorite

Petrology of silicate inclusions in the Sombrerete ungrouped iron meteorite: Implications for the origins of IIE‐type silicate‐bearing irons

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