Coesite and Stishovite: Stepwise Reversal Transformations

Dachille, Frank; Zeto, Robert J.; Roy, Rustum

doi:10.1126/science.140.3570.991

Cited by 59 publications

(25 citation statements)

References 5 publications

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“…Similar metastable transitions were observed by Dachille, et al (1963) and by Skinner and Fahey (1963). 2) Undetectable quartz or coesite nuclei may have been present in the starting material (concentrated from an impacted sandstone).…”

Section: Generalsupporting

confidence: 60%

Effect of Pressure and Temperature on the Reversal Transitions of Stishovite

Gigl

Dachille

1968

Meteoritics

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Section: Generalsupporting

confidence: 60%

Effect of Pressure and Temperature on the Reversal Transitions of Stishovite

Gigl

Dachille

1968

Meteoritics

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“…The strongest argument against high temperatures throughout the suevite is the preservation of stishovite (Horz, 1965;Stoffler, 1971). Stishovite decomposes in minutes at 500 "C to an amorphous or poorly ordered phase (Dachille et al, 1963;Horz, 1965). Its presence in the suevite is inconsistent with a high temperature for the bulk of the suevite.…”

Section: 'mentioning

confidence: 99%

Carbonate‐silicate liquid immiscibility upon impact melting: Ries Crater, Germany

Graup¹

1999

Meteorit & Planetary Scien

163

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Abstract-The 24 km diameter Ries impact crater in southern Germany is one of the most studied impact structures on Earth. The Ries impactor struck a Triassic to Upper Jurassic sedimentary sequence overlying Hercynian crystalline basement. At the time of impact (14.87 ? 0.36 Ma; Storzer el ul., 1995), the 350 m thick Malm limestone was present only to the south and east of the impact site. To the north and west, the Malm had been eroded away, exposing the underlying Dogger and Lias. The largest proportion of shocked target material is in the impact-melt-bearing breccia suevite. The suevite had been believed to be derived entirely from the crystalline basement. Calcite in the suevite has been interpreted as a postimpact hydrothermal deposit.From optical inspection of 540 thin sections of suevite from 32 sites, I find that calcite in the suevite shows textural evidence of liquid immiscibility with the silicate impact melt. Textural evidence of liquid immiscibility between silicate and carbonate melt in the Ries suevite includes carbonate globules within silicate glass, silicate globules embedded in carbonate, deformable and coalescing carbonate spheres within silicate glass, sharp menisci or cusps and budding between silicate and carbonate melt, fluidal textures and gas vesicles in carbonate schlieren, a quench crystallization sequence of the carbonate, spinifex textured quenched carbonate, separate carbonate spherules in the suevite mineral-fragment matrix, and inclusions of mineral fragments suspended in carbonate blebs. Given this evidence of liquid immiscibility, the carbonate in the suevite therefore has-like the silicate melt-a primary origin by impact-shock melting.Evidence of carbonate-silicate liquid immiscibility is abundant in the suevites from the southwest to east of the Ries crater. The rarer suevites to the west to northeast of the crater are nearly devoid of carbonate melts. This correspondence between the occurrence of outcropping limestones at the target surface and the formation of carbonate melt indicates that the Malm limestones are the source rocks of the carbonate impact melt. This correspondence shows that the suevites preserve a compositional memory of their source rocks. From the regional distribution of suevites with or without immiscible carbonate melts, it is inferred that the Ries impactor hit the steep Albtrauf escarpment at its toe, in an oblique impact from the north.

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“…However, gas adsorption measurements showed the absence of accessible pores leading to the conclusion that pressure may have closed the pores and trapped the carbon. Owing to the easy amorphization of stishovite at the low temperature (~300 °C; Dachille et al 1963) of calcination, we thought that plasma oxygen etching may be a possible technique for carbon removal from the pores. As mentioned above the carbon that initially fills the pores has the important role of preventing their collapse due to the high pressure and temperature.…”

Section: Introductionmentioning

confidence: 99%