Browsing by Author "Tschauner, Oliver"
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- ItemA previously unrecognized example of the shock-induced breakdown of biotite to garnet from the Steen River impact structure, Canada(2016) Walton, Erin L.; Sharp, Thomas G.; Hu, Jinping; Tschauner, OliverShock metamorphic effects from quartz and feldspar have been studied in detail, and to a lesser extent olivine and pyroxene. Less is known about how shock is manifest in other minerals such as double chain inosilicates, phyllosilicates, carbonates and sulfates. In this study, we investigate shock in crystalline basement rocks from the Steen River impact structure (SRIS), a 25-km diameter complex crater in NW Alberta, Canada.
- ItemHydrous olivine alteration on Mars and Earth(2020) Vaci, Zoltan; Agee, Carl B.; Herd, Christopher D. K.; Walton, Erin L.; Tschauner, Oliver; Ziegler, Karen; Prakapenka, Vitali B.; Greenberg, Eran; Monique-Thomas, SylviaHydrous alteration of olivine macrocrysts in a Martian olivine phyric basalt, NWA 10416, and a terrestrial basalt from southern Colorado are examined using SEM, EPMA, TEM, and µXRD techniques. The olivines in the meteorite contain linear nanotubes of hydrous material, amorphous areas, and fluid dissolution textures quite distinct from alteration identified in other Martian meteorites. Instead, they bear resemblance to terrestrial deuteric alteration features. The presence of the hydrous alteration phase Mg-laihunite within the olivines has been confirmed by µXRD analysis. The cores of the olivines in both Martian and terrestrial samples are overgrown by unaltered rims whose compositions match those of a separate population of groundmass olivines, suggesting that the core olivines are xenocrysts whose alteration preceded crystallization of the groundmass. The terrestrial sample is linked to deep crustal metasomatism and the “ignimbrite flare-up” of the Oligocene epoch. The comparison of the two samples suggests the existence of an analogous relatively water-rich magmatic reservoir on Mars.
- ItemInvestigating the response of biotite to impact metamorphism: examples from the Steen River impact structure, Canada(2018) Walton, Erin L.; Sharp, Thomas G.; Hu, Jinping; Tschauner, OliverImpact metamorphic effects from quartz and feldspar and to a lesser extent olivine and pyroxene have been studied in detail. Comparatively, studies documenting shock effects in other minerals, such as double chain inosilicates, phyllosilicates, carbonates, and sulfates, are lacking. In this study, we investigate impact metamorphism recorded in crystalline basement rocks from the Steen River impact structure (SRIS), a 25 km diameter complex crater in NW Alberta, Canada. An array of advanced analytical techniques was used to characterize the breakdown of biotite in two distinct settings: along the margins of localized regions of shock melting and within granitic target rocks entrained as clasts in a breccia. In response to elevated temperature gradients along shock vein margins, biotite transformed at high pressure to an almandine-Ca/Fe majorite-rich garnet with a density of 4.2 g cm−3. The shock-produced garnets are poikilitic, with oxide and silicate glass inclusions. Areas interstitial to garnets are vesiculated, in support of models for the formation of shock veins via oscillatory slip, with deformation continuing during pressure release. Biotite within granitic clasts entrained within the hot breccia matrix thermally decomposed at ambient pressure to produce a fine-grained mineral assemblage of orthopyroxene + sanidine + titanomagnetite. These minerals are aligned to the (001) cleavage plane of the original crystal. In this and previous work, the transformation of an inosilicate (pargasite) and a phyllosilicate (biotite) to form garnet, an easily identifiable, robust mineral, has been documented. We contend that in deeply eroded astroblemes, high-pressure minerals that form within or in the environs of shock veins may serve as one of the possibly few surviving indicators of impact metamorphism.
- ItemShock effects in new Martian olivine basalt Northwest Africa 10416: distinct from shergottites but akin Northwest Africa 8159(2016) Walton, Erin L.; Tschauner, Oliver; Herd, Christopher D. K.; Agee, Carl B.Martian meteorites record a range of shock effects associated with hypervelocity impact events on their parent body. The purpose of this study is to characterize shock deformation and transformation effects within and adjacent to shock veins in NWA 10416 and in non-veined regions of the host rock. New phases produced by shock, through crystallization or solid-state transfromation, can be used to estimate the shock pressure and the duration of the shock pulse to better understand the impact processes experienced by this sample.
- ItemThe Northwest Africa 10416 olivine-phyric shergottite: a product of multiple impact events on Mars?(2016) Walton, Erin L.; Herd, Christopher D. K.; Tschauner, Oliver; Agee, Carl B.Martian meteorites record shock effects associated with hypervelocity impact events on their parent planet, manifest as shock deformation or transformation of igneous minerals. The timing of Mars ejection can be approximated by the CRE age; however, the timing of shock metamorphism has been addressed by few studies. Recently, the first shergottite to preserve crystalline igneous feldspar was reported. In 2015, another martian olivine basalt, NWA 10416, was described. As one of the few martian meteorites to preserve igneous feldspar, NWA 10416 records shock conditions distinct from those of other shergottites within which plagioclase has been amorphized or melted. The purpose of this study is to characterize shock in NWA 10416.