Thulium anomalies and rare earth element patterns in meteorites and Earth: Nebular fractionation and the nugget effect

摘要: This study reports the bulk rare earth element (REEs, La–Lu) compositions of 41 chondrites, including 32 falls and 9 finds from carbonaceous (CI, CM, CO CV), enstatite (EH EL) ordinary (H, L LL) groups, as well 2 achondrites (aubrite). The measurements were done in dynamic mode using multi-collector inductively coupled plasma mass spectrometers (MC-ICPMS), allowing precise quantification mono-isotopic REEs (Pr, Tb, Ho Tm). CI-chondrite-normalized REE patterns (LaN/LuN; a proxy for fractionation light vs. heavy REEs) Eu anomalies chondrites show more scatter metamorphosed (petrologic types 4–6) than unequilibrated (types 1–3) chondrites. is due to parent-body redistribution various carrier phases during metamorphism. A model presented that predicts dispersion elemental isotopic ratios nugget effect when analyzed sample limited elements are concentrated minor grains. equilibrated reproduced by this model, considering 200 lm-size phosphates, which have high LaN/LuN negative anomalies. Terrestrial rocks samples display Tm �� 4.5% relative CI In contrast, CV (except Allende) no significant Allende chondrite shows large excess (� +10%). These similar those found group II refractory inclusions meteorites but much smaller magnitude. presence terrestrial suggests either (i) material inner part solar system was formed gas reservoir had been depleted dust carried positive or (ii) enriched not representative composition elements. new reference relevant bodies (CI * ) calculated subtracting 0.15% CI. observed rocks, indicate akin must represented small fraction constituents Earth. may be correlated with Ca planetary materials they both controlled addition removal fine-grained inclusions.