The brecciated texture of polymict eucrites: Petrographic investigations of unequilibrated meteorites from the Antarctic Yamato collection
We report on the petrography and mineralogy of five Yamato polymict eucrites to better constrain the formation and alteration of crustal material on differentiated asteroids. Each sample consists of different lithic clasts that altogether form four dominant textures and therefore appear to originate...
| Main Authors: | , , , , |
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| Format: | Text |
| Language: | English |
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FID GEO
2020
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| Subjects: | |
| Online Access: | https://dx.doi.org/10.23689/fidgeo-4519 https://e-docs.geo-leo.de/handle/11858/8865 |
| Summary: | We report on the petrography and mineralogy of five Yamato polymict eucrites to better constrain the formation and alteration of crustal material on differentiated asteroids. Each sample consists of different lithic clasts that altogether form four dominant textures and therefore appear to originate from closely related petrological areas within Vesta′s crust. The textures range from subophitic to brecciated, porphyritic, and quench-textured, that differ from section to section. Comparison with literature data for these samples is therefore difficult, which stresses that polymict eucrites are extremely complex in their petrography and investigation of only one thick section may not be representative for the host rock. We also show that sample Y-793548 consists of more than one lithic unit and must therefore be classified as polymict instead of monomict. The variety and nature of lithic textures in the investigated Yamato meteorites indicate shock events, intense post-magmatic thermal annealing, and secondary alteration. These postmagmatic features occur in different intensities, varying from clast to clast or among coexisting mineral fragments on a small, local scale. Several clasts within the eucrites studied have been modified by late-stage alteration processes that caused deposition of Fe-rich olivine and Fe enrichment along cracks crosscutting pyroxene crystals. However, formation of these secondary phases seems to be independent of the degree of thermal metamorphism observed within every type of clast, which would support a late-stage metasomatism model for their formation. |
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