Observations of high-velocity, weakly shocked ejecta from experimental impacts

Gratz, A. J.; Nellis, W. J.; Hinsey, N.

doi:10.1038/363522a0

Cited by 33 publications

(19 citation statements)

References 13 publications

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“…Modes for ejection mechanisms involve theoretical investigation by numerical simulations and are evaluated by studying the physical conditions recorded in Martian material that eventually makes its way to Earth for study after residence times of generally a few million years in space (e.g., Fritz et al 2005; see also Nyquist et al 2001 for compiled CRE ages). The spallation ejection mechanism, whereby solid material is accelerated at high velocity by stress wave interference (Melosh 1984(Melosh , 1985, has been supported by laboratory shock recovery experiments of Gratz et al (1993) and is most consistent with shock effects recorded in Martian meteorites (Fritz et al 2005). The result is a zone in which the pressure gradient, and not the absolute pressure, is extremely high.…”

Section: Ejection Of Martian Rockssupporting

confidence: 51%

Localized shock melting in lherzolitic shergottite Northwest Africa 1950: Comparison with Allan Hills 77005

Walton

Herd

2007

Meteorit & Planetary Scien

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) and chromite, embedded in an Fe-rich, Al-poor basaltic to picro-basaltic glass. Within the melt pockets strong thermal gradients (minimum 1 °C/μm) existed at the onset of crystallization, giving rise to a heterogeneous distribution of nucleation sites, resulting in gradational textures of olivine and chromite. Dendritic and skeletal olivine, crystallized in the melt pocket center, has a nucleation density (1.0 × 10 3 crystals/mm 2 ) that is two orders of magnitude lower than olivine euhedra near the melt margin (1.6 × 10 5 crystals/mm 2 ). Based on petrography and minor element abundances, melt pocket formation occurred by in situ melting of host rock constituents by shock, as opposed to melt injected into the lherzolitic target. Despite a common origin, NWA 1950 is shocked to a lesser extent compared to Allan Hills (ALH) 77005 (45-55 GPa). Assuming ejection in a single shock event by spallation, this places NWA 1950 near to ALH 77005, but at a shallower depth within the Martian subsurface. Extensive shock melt networks, the interconnectivity between melt pockets, and the ubiquitous presence of highly vesiculated plagioclase glass in ALH 77005 suggests that this meteorite may be transitional between discreet shock melting and bulk rock melting.

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Section: Ejection Of Martian Rockssupporting

confidence: 51%

Localized shock melting in lherzolitic shergottite Northwest Africa 1950: Comparison with Allan Hills 77005

Walton

Herd

2007

Meteorit & Planetary Scien

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“…Little is known about the nature and structure of all these Cristobalite-`x' phases [6,7]. For the same pressure range (above 10 GPa), several have reported amorphisation [4,8,9]; it is www.elsevier.nl/locate/cplett not clear how this is related to the phase transitions mentioned above. Recently, the a-PbO 2 -like silica was experimentally obtained in a mixture with stishovite in a laser-heated DAC at pressures above 70 GPa and temperatures above 2500 K [12].…”

Section: Introductionmentioning

confidence: 93%

Pressure-induced transformations of cristobalite

Dubrovinsky

Dubrovinskaia

Saxena

et al. 2001

Chemical Physics Letters

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“…Experimental (Gratz et al 1993) and observational evidence has forced a revision of this opinion. Most significantly, the SNC meteorites experienced shocks no greater than 45 GPa, with corresponding temperatures ≤ 600 C (Stoffler 2000, as cited by Mastrapa et al 2001).…”

Section: B Calculation Of Survival Fractionsmentioning

confidence: 99%