Evidence from Tm anomalies for non-CI refractory lithophile element proportions in terrestrial planets and achondrites
|Author(s)||Barrat Jean-Alix1, Dauphas N.2, 3, Gillet P.4, Bollinger C.5, Etoubleau Joel6, Bischoff A.7, Yamaguchi A.8, 9|
|Affiliation(s)||1 : Univ Bretagne Occidentale, Inst Univ Europeen Mer, CNRS, UMR 6538, Pl Nicolas Copern, F-29280 Plouzane, France.
2 : Univ Chicago, Dept Geophys Sci, Origins Lab, 5734 South Ellis Ave, Chicago, IL 60637 USA.
3 : Univ Chicago, Enrico Fermi Inst, 5734 South Ellis Ave, Chicago, IL 60637 USA.
4 : Ecole Polytech Fed Lausanne, Inst Condensed Matter Phys, Stn 3, CH-1015 Lausanne, Switzerland.
5 : Inst Univ Europeen Mer, CNRS, UMS 3113, Pl Nicolas Copern, F-29280 Plouzane, France.
6 : IFREMER, Ctr Brest, F-29280 Plouzane, France.
7 : Univ Munster, Inst Planetol, Wilhelm Klemm Str 10, D-48149 Munster, Germany.
8 : Natl Inst Polar Res, Tachikawa, Tokyo 1908518, Japan.
9 : Grad Univ Adv Studies, SOKENDAI, Sch Multidisciplinary Sci, Dept Polar Sci, Tachikawa, Tokyo 1908518, Japan.
|Source||Geochimica Et Cosmochimica Acta (0016-7037) (Pergamon-elsevier Science Ltd), 2016-03 , Vol. 176 , P. 1-17|
|WOS© Times Cited||24|
|Abstract||Thulium is a heavy rare earth element (REE) whose geochemical behavior is intermediate between Er and Yb, and that is not expected to be decoupled from these elements during accretion of planetary bodies and geological processes. However, irregularities in REE volatilities at higher temperature could have decoupled the REEs relative to one another during the early stages of condensation of the solar nebula. Indeed, positive Tm anomalies are found in some refractory inclusions from carbonaceous chondrites, and it is possible that large scale nebular reservoirs displaying positive or negative Tm anomalies were formed during the early history of the solar system. We analyzed a series of meteorites and terrestrial rocks in order to evaluate the existence of Tm anomalies in planetary materials. Relative to CIs (Ivuna-type carbonaceous chondrites), carbonaceous chondrites display unresolved or positive Tm anomalies, while most of the noncarbonaceous chondrites show slightly negative Tm anomalies. Quantification of these anomalies in terrestrial samples is complicated when samples display fractionated heavy REE patterns. Taking this effect into account, we show that the Earth, Mars, Vesta, the aubrite and ureilite parent bodies display small negative anomalies (Tm/Tm∗≈0.975), very similar to those found in ordinary and enstatite chondrites. We suggest that a slight negative Tm anomaly relative to CI is a widespread feature of the materials from the inner solar system. This finding suggests that CI chondrites may not be appropriate for normalizing REE abundance patterns of most planetary materials as they may be enriched in a high-temperature refractory component with non-solar composition. The presence of Tm anomalies at a bulk planetary scale is, to this day, the strongest piece of evidence that refractory lithophile elements are not present in constant proportions in planetary bodies.|