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Concentrations of siderophile elements in nonmagnetic fractions of Antarctic H‐ and L‐chondrites: A quantitative approach on weathering effects
Author(s) -
WELTEN K. C.
Publication year - 1999
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.1945-5100.1999.tb01750.x
Subject(s) - weathering , chondrite , meteorite , space weathering , geology , mineralogy , geochemistry , regolith , metal , astrobiology , metallurgy , materials science , asteroid , physics
— The nonmagnetic separates of Antarctic H‐ and L‐chondrite finds from the Lewis Cliff stranding area are enriched in Fe and siderophile elements such as Ni, Co, Cu, As, Ir, and Au, relative to those of non‐Antarctic falls. The siderophile enrichments are caused by the oxidation of metallic Fe‐Ni to nonmagnetic hydrous Fe‐Ni oxides. The concentrations of Fe, Ni, and Co in each sample were used to calculate the amount of oxidized metal, which serves as a quantitative measure of the degree of weathering. The amount of oxidized metal is generally between 1–10 wt% and shows a rough correlation with the qualitative A‐B‐C‐weathering classification for increasing rustiness. No clear correlation was found between weathering and terrestrial age, although meteorites older than 0.2 Ma contain on the average ∼50% more oxidized metal. Also, no correlation was found between the degree of weathering and the natural thermoluminescence (TL) level, which is dominated by the thermal history in space rather than by the thermal history in or on the Antarctic ice. The only significant parameter for the degree of weathering seems to be the location of find, with the most weathered specimens being found in a part of the stranding area where melt‐water ponds are known to occur. This observation confirms that the occasional presence of liquid water plays an important role in the Antarctic weathering process and explains the poor correlation of the degree of weathering of Antarctic meteorites with terrestrial age and surface exposure age.