Shock experiments with the H6 chondrite Kernouvé: Pressure calibration of microscopic shock effects

Schmitt, Rüdiger

doi:10.1111/j.1945-5100.2000.tb01435.x

Cited by 101 publications

(127 citation statements)

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“…A few melt pockets had also observed in the samples (Figure 3). The formation of the melt pockets is not related an equilibrium shock pressure and temperature experienced by whole rock, and it should be attributed to localized spikes of pressure and temperature appearing in shocked polycrystalline rocks [29,30].…”

Section: Discussionmentioning

confidence: 99%

High-pressure polymorph of TiO2-II from the Xiuyan crater of China

Chen

Xie

et al. 2013

Chin. Sci. Bull.

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Abundant TiO 2 -II, a high-pressure polymorph of titanium dioxide, was found in the gneiss fragments of impact-produced breccias from the Xiuyan crater. Rutile in the gneiss was severely fragmented and fine-grained clasts less than 2 m in size had been transformed to TiO 2 -II. Irregular thin layered TiO 2 -II is also observed in coarse-grained rutile fragments, where the TiO 2 -II layers distributes along fractures and cracks in rutile. About 30 percent of rutile in the gneiss had been transformed to TiO 2 -II. Fine grains of TiO 2 -II display light bluish grey to light yellow brown in plane-polarized reflected light. Crystallographic investigation shows that TiO 2 -II has an orthorhombic structure with space group Pbcn. The cell parameters are a=4.543(1) Å, b=5.491(9) Å and c=4.895(2) Å. Its empirical formula calculated on the basis of two oxygen atoms can be written as (Ti 0.985 Fe 0.008 Nb 0.006 -Si 0.003 Zr 0.001 ) 1.003 O 2 , or simply formula TiO 2 . According to the shock effects of quartz and feldspars, the peak shock pressure and post-shock temperature in the TiO 2 -II-bearing gneiss are estimated to be between 35 and 43 GPa and 300-900°C, respectively. The finding of TiO 2 -II in the shock-metamorphosed gneiss provides another mineral physics evidence for shock origin of the Xiuyan crater. Rutile, a titanium dioxide, is a common accessory mineral in various types of rocks. At high pressure, rutile can be transformed into high-pressure polymorphs of TiO 2 -II (-PbO 2 ), baddeleyite, orthorhombic I and cotunnite phases with increasing pressure [1]. High-pressure polymorphs of baddeleyite, orthorhombic-I and cotunnite-type TiO 2 reverse to TiO 2 -II on decompression. TiO 2 -II is the only highpressure polymorph that can be recovered experimentally at ambient conditions [2]. i  - had been firstly synthesized by static compression experiment [3]. A number of static compression experiments succeed in the transition of rutile to TiO 2 -II at pressure range between 4 and 12 GPa and temperature between 400 and 1500°C [3][4][5][6][7]. Shock-loading experiments revealed that rutile transforms to i  - at peak shock pressure from 20 to 100 GPa [8][9][10]. The formation of natural TiO 2 -II could be related to highpressure endogenic geological processes or bolide impact events. Occurrence of natural TiO 2 -II had been previously reported in ultrahigh-pressure metamorphic rocks [11,12], mantle-derived rocks [13], terrestrial impact structures [14][15][16], and tektite [17]. However, the mineralogical features and the formation conditions of natural TiO 2 -II still needs to be further investigated because of the very limited material that had been found.The Xiuyan crater is a recently confirmed impact structure in China. The target rocks of the crater were shock-metamorphosed, from which impact-produced breccia, coesite, planar deformation features in quartz have been identified [18][19][20]. In this paper, we report the occurrence and mineralogical features of TiO 2 -IIin the impact-produced breccias

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Section: Discussionmentioning

confidence: 99%

High-pressure polymorph of TiO2-II from the Xiuyan crater of China

Chen

Xie

et al. 2013

Chin. Sci. Bull.

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“…These pressure estimates are based on experimental data (Kieffer et al, 1976;Schaal and Hörz, 1977;Schmitt, 2000). In addition, high pressure phases such as very dense post-stishovite polymorphs of SiO 2 have been discovered in Shergotty (Sharp et al, 1999;El Goresy et al, 2000).…”

Section: Evidence Of Shockmentioning

confidence: 99%

Ages and Geologic Histories of Martian Meteorites

Nyquist

Bogard

Shih

et al. 2001

Space Sciences Series of ISSI

376

558

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Abstract.We review the radiometric ages of the 16 currently known Martian meteorites, classified as 11 shergottites (8 basaltic and 3 lherzolitic), 3 nakhlites (clinopyroxenites), Chassigny (a dunite), and the orthopyroxenite ALH84001. The basaltic shergottites represent surface lava flows, the others magmas that solidified at depth. Shock effects correlate with these compositional types, and, in each case, they can be attributed to a single shock event, most likely the meteorite's ejection from Mars. Peak pressures in the range 15 − 45 GPa appear to be a "launch window": shergottites experienced ∼30 − 45 GPa, nakhlites ∼20 ± 5 GPa, Chassigny ∼35 GPa, and ALH84001 ∼35 − 40 GPa. Two meteorites, lherzolitic shergottite Y-793605 and orthopyroxenite ALH84001, are monomict breccias, indicating a two-phase shock history in toto: monomict brecciation at depth in a first impact and later shock metamorphism in a second impact, probably the ejection event.Crystallization ages of shergottites show only two pronounced groups designated S 1 (∼175 Myr), including 4 of 6 dated basalts and all 3 lherzolites, and S 2 (330 − 475 Myr), including two basaltic shergottites and probably a third according to preliminary data. Ejection ages of shergottites, defined as the sum of their cosmic ray exposure ages and their terrestrial residence ages, range from the oldest (∼20 Myr) to the youngest (∼0.7 Myr) values for Martian meteorites. Five groups are distinguished and designated S Dho (one basalt, ∼20 Myr), S L (two lherzolites of overlapping ejection ages, 3.94 ± 0.40 Myr and 4.70 ± 0.50 Myr), S (four basalts and one lherzolite, ∼2.7 − 3.1 Myr), S DaG (two basalts, ∼1.25 Myr), and S E (the youngest basalt, 0.73 ± 0.15 Myr). Consequently, crystallization age group S 1 includes ejection age groups S L , S E and 4 of the 5 members of S, whereas S 2 includes the remaining member of S and one of the two members of S DaG . Shock effects are different for basalts and lherzolites in group S/S 1 . Similarities to the dated meteorite DaG476 suggest that the two shergottites that are not dated yet belong to group S 2 . Whether or not S 2 is a single group is unclear at present. If crystallization age group S 1 represents a single ejection event, pre-exposure on the Martian surface is required to account for ejection ages of S L that are greater than ejection ages of S, whereas secondary breakup in space is required to account for ejection ages of S E less than those of S. Because one member of crystallization age group S 2 belongs to ejection group S, the maximum number of shergottite ejection events is 6, whereas the minimum number is 2.Crystallization ages of nakhlites and Chassigny are concordant at ∼1.3 Gyr. These meteorites also have concordant ejection ages, i.e., they were ejected together in a single event (NC). Shock effects vary within group NC between the nakhlites and Chassigny.The orthopyroxenite ALH84001 is characterized by the oldest crystallization age of ∼4.5 Gyr. Its secondary carbonates are ∼3.9 Gyr old, an age corresponding t...

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“…2b and 2c). Thus, TEM can lead to the overestimation of shock pressures if applied to features that were calibrated with optical microscopy (e.g., Schmitt 2000). The stringers of opx glass that line the boundaries between opx and some fracturefilling carbonates (Fig.…”

Section: Orthopyroxene and Shock History Of Alh 84001mentioning

confidence: 99%

Transmission electron microscopy of minerals in the martian meteorite Allan Hills 84001

Barber

Scott

2003

Meteorit & Planetary Scien

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Abstract-We have studied carbonate and associated oxides and glasses in a demountable section of Allan Hills 84001 (ALH 84001) using optical, scanning, and transmission electron microscopy (TEM) to elucidate their origins and the shock history of the rock. Massive, fracture-zone, and fracture-filling carbonates in typical locations were characterized by TEM, X-ray microanalysis, and electron diffraction in a comprehensive study that preserved textural and spatial relationships. Orthopyroxene is highly deformed, fractured, partially comminuted, and essentially unrecovered. Lamellae of diaplectic glass and other features indicate shock pressures >30 GPa. Bridging acicular crystals and foamy glass at contacts of orthopyroxene fragments indicate localized melting and vaporization of orthopyroxene. Carbonate crystals are >5 mm in size, untwinned, and very largely exhibit the R3c calcite structure. Evidence of plastic deformation is generally found mildly only in fracture-zone and fracture-filling carbonates, even adjacent to highly deformed orthopyroxene, and appears to have been caused by low-stress effects including differential shrinkage. High dislocation densities like those observed in moderately shocked calcite are absent. Carbonate contains impactderived glasses of plagioclase, silica, and orthopyroxene composition indicating brief localized impact heating. Stringers and lenses of orthopyroxene glass in fracture-filling carbonate imply flow of carbonates and crystallization during an impact. Periclase (MgO) occurs in magnesite as 30-50 nm crystals adjacent to voids and negative crystals and as ~1 mm patches of 3 nm crystals showing weak preferred orientation consistent with (111) MgO //(0001) carb , as observed in the thermal decomposition of CaCO 3 to CaO. Magnetite crystals that are epitaxially oriented at voids, negative crystals, and microfractures clearly formed in situ. Fully embedded, faceted magnetites are topotactically oriented, in general with (111) mag //(0001) carb , so that their oxygen layers are aligned. In optically opaque rims, magnetites are more irregularly shaped and, except for the smallest crystals, poorly aligned. All magnetite and periclase crystals probably formed by exsolution from slightly non-stoichiometric, CO 2 -poor carbonate following impact-induced thermal decomposition. Any magnetites that existed in the rock before shock heating could not have preserved evidence for biogenic activity.

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Shock experiments with the H6 chondrite Kernouvé: Pressure calibration of microscopic shock effects

Cited by 101 publications

References 42 publications

High-pressure polymorph of TiO2-II from the Xiuyan crater of China

High-pressure polymorph of TiO2-II from the Xiuyan crater of China

Ages and Geologic Histories of Martian Meteorites

Transmission electron microscopy of minerals in the martian meteorite Allan Hills 84001

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