Shock‐induced color changes in nontronite: Implications for the Martian fines

Weldon, Ray J.; Thomas, Warren M.; Boslough, M. B.; Ahrens, Thomas J.

doi:10.1029/jb087ib12p10102

Cited by 21 publications

(19 citation statements)

References 37 publications

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“…Huck et al, 1977) and the mineralogical causes of the color are currently in dispute (e.g. Smith, 1979, p. 50-52, for early literature;Weldon et al, 1982;Moskowitz and Hargraves, 1981;McCord et al, 1982;Singer, 1982;Sherman et al, 1982). Perhaps brown olivine should be added to nontronite and various iron oxides as possible coloring agents for rocks on Mars.…”

Section: Discussionmentioning

confidence: 99%

Achondrite Alha77005: Alteration of Chromite and Olivine

1984

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The olivine crystals of the 77005 achondrite are brown except for colorless shock lamellae, mottled patches, and grains adjacent to pools of impact melt. Sporadic dark alteration patches in brown olivine and Cr‐rich spinel gave the following average electron‐microprobe analyses: (olivine) P2O5 0.9, SiO2 57.9, TiO2 0, Al2O3 0.7, Cr2O3 0.4, V2O3 0, Fe2O3 (assumed oxidation state) 17.0, MgO 1.6, CaO 0.2, Na2O 0, K2O 1.8, SO3 (assumed oxidation state) 9.2, Cl 0.1, sum 89.8 wt. %; (spinel) P2O53.5, SiO22.1, TiO2.2.2, Al2O32.1, Cr2O3 13.4, V2O3 0.8, Fe2O3 40.7, MgO 0.9, CaO 0.1, Na2O 0, K2O 2.0, SO3 11.1, Cl 0.1, sum 79.0 wt.%. Ion‐microprobe analyses revealed H in both. Rare orange patches in brown olivine from another area gave SiO2 33–35, FeO 30‐28, MgO 28–32, sum 93 wt. %. Thermal metamorphism under dry oxidizing conditions is discussed as a possible alternative to shock‐induced oxidation for generation of the brown olivine (McSween and Stöffler). Because alteration patches transgress shock lamellae, and because sulfatic alteration occurs in fusion crusts of Antarctic meteorites (Gibson et al., 1983), alteration of the 77005 achondrite at the Antarctic surface is preferred to a complex series of processes needed for pre‐terrestrial alteration.

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Section: Discussionmentioning

confidence: 99%

Achondrite Alha77005: Alteration of Chromite and Olivine

1984

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“…The Weldon et al (1982) study, as well as further experiments and characterization by Boslough et a1 (1986), showed that Riverside non tronite that has been shocked or thermally altered achieves colors that span those found on Mars and contains as much ferromagnetic material as the Martian fines do. These studies concluded on that basis that nontronite cannot be excluded as a major constituent of the Martian soil because of known chemical, mineralogical, spectroscopic, or physical properties.…”

Section: Wh Y Is Mars Red?mentioning

confidence: 94%

“…Thus, a substantial fraction of the chemically altered Martian surface material has also been reshocked. Weldon et al (1982) first suggested that the color of the Martian surface materials and their spectral reflectance properties have been modified by their exposure to shock processing. They based their hypothesis on the results of shock experiments on Riverside nontronite, a candidate for the major mineral equivalent in the Martian fines.…”

Section: Wh Y Is Mars Red?mentioning

confidence: 99%

Shock Modification and Chemistry and Planetary Geologic Processes

Boslough¹

1991

Annu. Rev. Earth Planet. Sci.

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The second half of the twentieth century has seen a revolution in the Earth and planetary sciences. One radically new concept is that hypervelocity impact is a major process at work in the solar system. Only in the last few decades has it become fully accepted that the Earth, the other terrestrial planets, the Moon, the icy satellites, and the asteroids all have surfaces that are heavily modifi ed by a history of impact. Such modifi cation is evident from the cratered surfaces of these solar system objects, the micro structures of many meteorites, and the properties of the lunar regolith, all of which show evidence of repeated exposure to impacts and resulting shock waves.Along with the appreciation of the importance of impact as a surface process, accretionary models for planetary formation have been advanced and accepted. For example, it is now clear that shock heating was a primary contributor to thc thermal state of planets as they grew. In the last decade, hypotheses have been embraced that require impacts of various sizes to explain events ranging from the origin of the Moon to the Cre taceous-Tertiary mass extinction to the ejection of rocks (thc SNC meteor ites) from the surface of Mars. Serious hypotheses have included impact as the cause of phenomena as varied as periodic biologic extinctions and magnetic pole reversals. Further ANNUAL REVIEWS 102 BOSLOUGHIn light of this newly realized importance of impact, an assessment is in order of the chemical role that impact-induced shock waves have played. A historic event, the Tunguska meteor, which involved shock compression of the atmosphere of the Earth, serves as a dramatic example. When shock waves generated by lightning or a nuclear explosion interact with the atmosphere, they can cause a reaction between molecular oxygen and nitrogen to form nitric oxide. Such shock-induced gas-phase reactions can also result from the penetration of the atmosphere by a meteoroid. As much as 3 x 1010 kg of nitric oxide were produced by the shock wave from the Tunguska meteor, which devastated a large area of forest when it exploded over Siberia in 19 08 (Turco et al 19 82). Soon afterward, the surrounding forest experienced unprecedented rates of growth. The trees had probably been fertilized by nitrogen compounds that had formed subsequent to the event by reactions between the shock-generated nitric oxide and atmospheric oxygen (Melosh 19 89). A similar sequence of shock induced reactions has been suggested for generating large quantities of nitric and other acids, destroying life at the end of the Cretaceous era (Lewis et aI 1982), and Fegley et al (1 986) have proposed that atmospheric shock synthesis generated important precursors for the abiotic production of the fi rst complex organic molecules.Shock effects in solids are probably of even greater concern. It is now known that essentially all of the solid material in the solar system has, at some time during its history, been subjected to shock processing. From the rapidly growing body of research on shock waves in ...

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“…This conclusion supports the early findings of Boslough et al [1986], who first observed that color change in shocked nontronite samples differed from that induced by annealing (thermal alteration). It also suggests that the color changes observed in shocked nontronite by Weldon et al [1982] were likely a result of both shock-induced stress and thermal alteration rather than shock-induced thermal alteration alone. It is important to understand the effects of shock and temperature as separate processes because (with the exception of very large impacts) the nonlinear relationship between pressure and temperature in impacts Figure 10.…”

Section: Comparison Of Shock and Thermal Alterationmentioning

confidence: 99%

“…Shock effects have also been invoked to explain the color of the Martian surface. In particular, Weldon et al [] observed that a sample of Riverside nontronite reddened and darkened after experimental impacts between 18 and 30 GPa. Using optical microscopy, X‐ray diffractometry, 57 Fe Mössbauer spectroscopy, and IR spectroscopy, they determined that partial dehydroxylation changed the Fe coordination state and shifted characteristic Fe 3+ /O 2− charge transfer features into the visible wavelength region, producing a redder, darker nontronite sample.…”

Section: Introductionmentioning

confidence: 99%

Structural and spectroscopic changes to natural nontronite induced by experimental impacts between 10 and 40 GPa

Friedlander

Glotch

Bish

et al. 2015

J. Geophys. Res. Planets

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Many phyllosilicate deposits remotely detected on Mars occur within bombarded terrains. Shock metamorphism from meteor impacts alters mineral structures, producing changed mineral spectra. Thus, impacts have likely affected the spectra of remotely sensed Martian phyllosilicates. We present spectral analysis results for a natural nontronite sample before and after laboratory-generated impacts over five peak pressures between 10 and 40 GPa. We conducted a suite of spectroscopic analyses to characterize the sample's impact-induced structural and spectral changes. Nontronite becomes increasingly disordered with increasing peak impact pressure. Every infrared spectroscopic technique used showed evidence of structural changes at shock pressures above~25 GPa. Reflectance spectroscopy in the visible near-infrared region is primarily sensitive to the vibrations of metal-OH and interlayer H 2 O groups in the nontronite octahedral sheet. Midinfrared (MIR) spectroscopic techniques are sensitive to the vibrations of silicon and oxygen in the nontronite tetrahedral sheet. Because the tetrahedral and octahedral sheets of nontronite deform differently, impact-driven structural deformation may contribute to differences in phyllosilicate detection between remote sensing techniques sensitive to different parts of the nontronite structure. Observed spectroscopic changes also indicated that the sample's octahedral and tetrahedral sheets were structurally deformed but not completely dehydroxylated. This finding is an important distinction from previous studies of thermally altered phyllosilicates in which dehydroxylation follows dehydration in a stepwise progression preceding structural deformation. Impact alteration may thus complicate mineral-specific identifications based on the location of OH-group bands in remotely detected spectra. This is a key implication for Martian remote sensing arising from our results.

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Shock‐induced color changes in nontronite: Implications for the Martian fines

Abstract: Abstract

Cited by 21 publications

References 37 publications

Achondrite Alha77005: Alteration of Chromite and Olivine

Achondrite Alha77005: Alteration of Chromite and Olivine

Shock Modification and Chemistry and Planetary Geologic Processes

Structural and spectroscopic changes to natural nontronite induced by experimental impacts between 10 and 40 GPa

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