|Titre||Electron microprobe and LA-ICP-MS analyses of ilmenite from lunar samples|
|Auteur||Morisset, C -E; Jackson, S; Williamson, M -C; Hipkin, V; Tait, K|
|Source||Goldschmidt 2012 conference abstracts; 2012 p. 2135|
|Liens||Online - En ligne |
|Séries alt.||Secteur des sciences de la Terre, Contribution externe 20120111|
|Réunion||22nd V.M. Goldschmidt Conference; Montreal; CA; juin 24-29, 2012|
|Media||en ligne; numérique|
|Sujets||méthodes analytiques; analyse par spectromètre de masse; ilménite; régolithes; analyses des éléments en trace; analyses des éléments majeurs; géologie extraterrestre; minéralogie; géochimie|
|Programme||Division de la CGC du Centre du Canada|
|Diffusé||2012 01 01|
|Résumé||(disponible en anglais seulement)|
Oxygen can be liberated from ilmenite at lower temperature than from silicates present in the lunar regolith, making ilmenite a key resource for human
settlement on the Moon. Major and trace element concentrations of ilmenite contained in twelve samples selected from the six Apollo landing sites (10 basalts, one impact melt, and one impact breccia) and in one lunar meteorite (NEA 001) have been
determined using electron microprobe and LA-ICP-MS. These analyses help us to understand the role of ilmenite in the crystallization of magma on the Moon and to determine if the ilmenite from different rock types has a specific chemical signature.
Ilmenite can reach a modal proportion of up to 20% in basaltic rocks. Some ilmenite grains contain rutile, Cr-spinel and baddeleyite needles. The TiO2 in the analyzed ilmenite from the Apollo samples varies from 52.4 to 55.9 wt% while it is
noticeably lower in the meteorite sample (i.e. 51.7 to 52.8 wt%). In all samples, FeO varies from 37.4 to 46.7 wt% and MgO from 0.1 to 5.1 wt% except in the impact melt where it is higher (5.3-5.7 wt%). The largest variation observed in MgO within an
ilmenite grain is of 0.3 wt% (e.g. 4.7-5.0 MgO wt%), implying that the observed variation between grains cannot be attributed to mineral zoning. So far, three basaltic samples have been analyzed by LA-ICP-MS. Cr varies from 1080 to 7580 ppm, V varies
from 80 to 453 ppm and both elements are positively correlated with MgO. Zr (123-2330ppm) and Hf (5.95-85 ppm) concentrations are highest in the baddeleyite-bearing ilmenite grains. Nb (20-107 ppm) and Ta (1.85-8.52 ppm) are positively correlated but
are not well correlated with Zr or Hf. REE patterns show enrichment in HREE (CeN/LuN: 0.0001-0.005) with a strong negative Eu anomaly (Eu/Eu* from 0.003 to 0.413). The ratio of MgO vs TiO2 of the ilmenite permit discrimination of what type of sample
the ilmenite is from. Ilmenite from the basaltic samples form a trend (n=355; slope=1.89; r2=0.86) that is richer in TiO2 for the same MgO than the impact breccias (n=11; slope=1.5; r2=0.91) and the meteorite (n=10; slope=4.38; r2=0.42) samples.
LA-ICP-MS analysis of the remaining samples will permit evaluation of whether the observed geochemical distinctions between the three sample groups are identifiable using trace elements.