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Thermal history of Northwest Africa 5073––A coarse‐grained Stannern‐trend eucrite containing cm‐sized pyroxenes and large zircon grains
Author(s) -
ROSZJAR Julia,
METZLER Knut,
BISCHOFF Addi,
BARRAT JeanAlix,
GEISLER Thorsten,
GREENWOOD Richard C.,
FRANCHI Ian A.,
KLEMME Stephan
Publication year - 2011
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/j.1945-5100.2011.01265.x
Subject(s) - zircon , pyroxene , geology , plagioclase , geochemistry , meteorite , melt inclusions , phenocryst , silicate , tridymite , achondrite , olivine , partial melting , mineralogy , chondrite , quartz , mantle (geology) , astrobiology , chemistry , cristobalite , paleontology , physics , organic chemistry
Abstract– We report on the bulk chemical composition, petrology, oxygen isotopic composition, trace element composition of silicates, and degree of self‐irradiation damage on zircon grains of the eucrite Northwest Africa (NWA) 5073 to constrain its formation and postcrystallization thermal history, and to discuss their implications for the geologic history of its parent body. This unequilibrated and unbrecciated meteorite is a new member of the rare Stannern‐trend eucrites. It is mainly composed of elongated, zoned pyroxene phenocrysts up to 1.2 cm, plagioclase laths up to 0.3 cm in length, and is rich in mesostasis. The latter contains zircon grains up to 30 μm in diameter, metal, sulfide, tridymite, and Ca‐phosphates. Textural observations and silicate compositions, coupled with the occurrence of extraordinary Fe‐rich olivine veins that are restricted to large pyroxene laths, indicate that NWA 5073 underwent a complex thermal history. This is also supported by the annealed state of zircon grains inferred from μ‐Raman spectroscopic measurements along with U and Th data obtained by electron probe microanalyses.