Shock metamorphism in plagioclase and selective amorphization
Autor: | Martin Lee, Ludovic Ferrière, Luke Daly, Lidia Pittarello, Annemarie E. Pickersgill |
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Rok vydání: | 2019 |
Předmět: |
Shock wave
Materials science Shatter cone engineering.material 010502 geochemistry & geophysics Feldspar 01 natural sciences Article Shock metamorphism deformation localization Silicate minerals 0103 physical sciences Planar deformation features Plagioclase electron backscatter diffraction shock metamorphism Petrology plagioclase feldspar 010303 astronomy & astrophysics 0105 earth and related environmental sciences Articles planar deformation features amorphization Shock (mechanics) Geophysics Space and Planetary Science visual_art visual_art.visual_art_medium engineering |
Zdroj: | Meteoritics & Planetary Science |
ISSN: | 1086-9379 |
Popis: | Plagioclase feldspar is one of the most common rock‐forming minerals on the surfaces of the Earth and other terrestrial planetary bodies, where it has been exposed to the ubiquitous process of hypervelocity impact. However, the response of plagioclase to shock metamorphism remains poorly understood. In particular, constraining the initiation and progression of shock‐induced amorphization in plagioclase (i.e., conversion to diaplectic glass) would improve our knowledge of how shock progressively deforms plagioclase. In turn, this information would enable plagioclase to be used to evaluate the shock stage of meteorites and terrestrial impactites, whenever they lack traditionally used shock indicator minerals, such as olivine and quartz. Here, we report on an electron backscatter diffraction (EBSD) study of shocked plagioclase grains in a metagranite shatter cone from the central uplift of the Manicouagan impact structure, Canada. Our study suggests that, in plagioclase, shock amorphization is initially localized either within pre‐existing twins or along lamellae, with similar characteristics to planar deformation features (PDFs) but that resemble twins in their periodicity. These lamellae likely represent specific crystallographic planes that undergo preferential structural failure under shock conditions. The orientation of preexisting twin sets that are preferentially amorphized and that of amorphous lamellae is likely favorable with respect to scattering of the local shock wave and corresponds to the “weakest” orientation for a specific shock pressure value. This observation supports a universal formation mechanism for PDFs in silicate minerals. |
Databáze: | OpenAIRE |
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