High-pressure phases in shock-induced melt of the unique highly shocked LL6 chondrite Northwest Africa 757

1Hu, J., 1Sharp, T. G
1School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA

Northwest Africa 757 is unique in the LL chondrite group because of its abundant shock-induced melt and high-pressure minerals. Olivine fragments entrained in the melt transform partially and completely into ringwoodite. Plagioclase and Ca-phosphate transform to maskelynite, lingunite, and tuite. Two distinct shock-melt crystallization assemblages were studied by FIB-TEM analysis. The first melt assemblage, which includes majoritic garnet, ringwoodite plus magnetite-magnesiowüstite, crystallized at pressures of 20–25 GPa. The other melt assemblage, which consists of clinopyroxene and wadsleyite, solidified at ~15 GPa, suggesting a second veining event under lower pressure conditions. These shock features are similar to those in S6 L chondrites and indicate that NWA 757 experienced an intense impact event, comparable to the impact event that disrupted the L chondrite parent body at 470 Ma.

Reference
Hu J, Sharp TG (2016) High-pressure phases in shock-induced melt of the unique highly shocked LL6 chondrite Northwest Africa 757.
Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12672]
Published by arrangement with John Wiley & Sons

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