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High‐pressure phases in shock‐induced melt of the unique highly shocked LL 6 chondrite Northwest Africa 757
Author(s) -
Hu Jinping,
Sharp Thomas G.
Publication year - 2016
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/maps.12672
Subject(s) - ringwoodite , chondrite , shock metamorphism , geology , plagioclase , olivine , geochemistry , meteorite , parent body , mineralogy , astrobiology , paleontology , physics , quartz
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 GP a. The other melt assemblage, which consists of clinopyroxene and wadsleyite, solidified at ~15 GP a, 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.