TY - JOUR
T1 - Chemical alteration and REE mobilization in meteorites from hot and cold deserts
AU - Crozaz, Ghislaine
AU - Floss, Christine
AU - Wadhwa, Meenakshi
N1 - Funding Information:
We gratefully acknowledge the Smithsonian Institution, the Meteorite Working Group, the Japanese National Institute for Polar Research, the Planetary Studies Foundation Institute for Meteorite and Polar Studies, Jean-Alix Barrat, Addi Bischoff, Takashi Mikouchi and J. Zipfel who provided thin sections, as well as Kuni Nishiizumi who provided terrestrial ages. Laura Lundberg made the first observations of Ce anomalies in the Antarctic shergottite ALHA77005, Weibiao Hsu analyzed some of the eucrites, and Jay Reid helped in the analysis of the winonaite. Thoughtful reviews by J. A. Barrat, T. McCoy, D. Mittlefehldt and H. Palme are gratefully acknowledged. This work was supported by NSF grant EAR 9980394 (P. I., G. Crozaz).
PY - 2003/12/15
Y1 - 2003/12/15
N2 - The effects of terrestrial weathering on REE mobilization are evaluated for a variety of uncommon meteorites found in Antarctica and in hot deserts. The meteorites analyzed include 7 non-cumulate eucrites, 10 shergottites, 3 nakhlites, 2 lunar meteorites, 4 angrites, 10 acapulcoites, 1 winonaite, and 1 brachinite. In-situ concentration measurements of lanthanides and selected other minor and trace elements were made on individual grains by secondary ion mass spectrometry (SIMS). In Antarctic meteorites, oxidation converts Ce3+ to Ce4+, which is less soluble than the trivalent REE, resulting in Ce anomalies. The mineral most affected is low-Ca pyroxene. However, not all grains of a given mineral are, and distinct analyses of a single grain can even yield REE patterns with and without Ce anomalies. The effect is most pronounced for Antarctic eucrites in which Ce anomalies are observed not only in individual minerals but also in whole rock samples. Although Ce anomalies are observed in meteorites from hot deserts as well, the most characteristic signs of chemical alteration in this environment are a LREE enrichment with a typical crustal signature, as well as Sr, Ba and U contaminations. These can modify the whole rock REE patterns and disturb the isotope systematics used to date these objects. The LREE contamination is highly heterogeneous, affecting some grains and not others of a given mineral (mainly olivine and low-Ca pyroxene, the two minerals with the lowest REE concentrations). The major conduit for REE movement is through shock-induced cracks and defects, and the highest levels of contamination are found in altered material filling such veins and cracks. Meteorites that experienced low shock levels and those that are highly recrystallized are the least altered.
AB - The effects of terrestrial weathering on REE mobilization are evaluated for a variety of uncommon meteorites found in Antarctica and in hot deserts. The meteorites analyzed include 7 non-cumulate eucrites, 10 shergottites, 3 nakhlites, 2 lunar meteorites, 4 angrites, 10 acapulcoites, 1 winonaite, and 1 brachinite. In-situ concentration measurements of lanthanides and selected other minor and trace elements were made on individual grains by secondary ion mass spectrometry (SIMS). In Antarctic meteorites, oxidation converts Ce3+ to Ce4+, which is less soluble than the trivalent REE, resulting in Ce anomalies. The mineral most affected is low-Ca pyroxene. However, not all grains of a given mineral are, and distinct analyses of a single grain can even yield REE patterns with and without Ce anomalies. The effect is most pronounced for Antarctic eucrites in which Ce anomalies are observed not only in individual minerals but also in whole rock samples. Although Ce anomalies are observed in meteorites from hot deserts as well, the most characteristic signs of chemical alteration in this environment are a LREE enrichment with a typical crustal signature, as well as Sr, Ba and U contaminations. These can modify the whole rock REE patterns and disturb the isotope systematics used to date these objects. The LREE contamination is highly heterogeneous, affecting some grains and not others of a given mineral (mainly olivine and low-Ca pyroxene, the two minerals with the lowest REE concentrations). The major conduit for REE movement is through shock-induced cracks and defects, and the highest levels of contamination are found in altered material filling such veins and cracks. Meteorites that experienced low shock levels and those that are highly recrystallized are the least altered.
UR - http://www.scopus.com/inward/record.url?scp=0347577836&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0347577836&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2003.08.008
DO - 10.1016/j.gca.2003.08.008
M3 - Article
AN - SCOPUS:0347577836
SN - 0016-7037
VL - 67
SP - 4727
EP - 4741
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 24
ER -