^1,2,3Liam D. Peterson,³Megan E. Newcombe,⁴Conel M.O’D. Alexander,⁴Jianhua Wang,^1,2,5Sune G. Nielsen
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.04.009]
¹Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02540, United States
²NIRVANA Labs, Woods Hole Oceanographic Institution, Woods Hole, MA 02540, United States
³Department of Geology, University of Maryland, College Park, MD 20740, United States
⁴Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC 20015, United States
⁵CRPG, CNRS, Université de Lorraine, 15 rue Notre Dame des Pauvres, 54501 Vandoeuvre lès Nancy, France
Copyright Elsevier

Erg Cech 002 (EC 002) is an andesitic achondrite, the earliest formed achondrite identified to date, and is a rare sample of primary melts that formed crusts on the first generation(s) of planetesimals. Given that EC 002 represents a primary or primitive melt and that H and F are incompatible during silicate partial melting, EC 002 may be a H- and F-rich material relative to previously studied achondrites. We measured the H2O (total H quantified as H2O) and F contents of low-Ca pyroxene xenocrysts (∼4– 12 µg/g H2O; <0.5 µg/g F), groundmass augite (∼5 – 10 µg/g H2O; <2.2 µg/g F), albitic feldspar (∼2– 5 µg/g H2O; <0.5 µg/g F), and a silica-rich phase (∼28– 30 µg/g H2O; ∼0.7– 2.5 µg/g F) in EC 002 by Nanoscale Secondary Ion Mass Spectrometry. We use a single-stage equilibrium batch melting model to provide a first-order reconstruction of the EC 002 parent body H2O (∼7– 200 µg/g H2O) and F (∼0.44– 2.4 µg/g F) contents, which are depleted relative to chondrites and the bulk Earth. This requires the first generation(s) of planetesimals to have either accreted from volatile-poor materials or undergone extensive volatile loss, supporting the idea that Earth acquired its H2O budget from thermally primitive materials.

¹M. E. Varela,²J. Roszjar,³P. Sylvester,^1,4L. Garcia
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14360]
¹Instituto de Ciencias Astronómicas, de la Tierra y del Espacio (ICATE), CONICET-San Juan, San Juan, Argentina
²Department of Mineralogy and Petrography, Natural History Museum Vienna, Vienna, Austria
³Department of Geosciences, Texas Tech University, Lubbock, Texas, USA
⁴Instituto de Mecánica Aplicada, Universidad Nacional de San Juan, San Juan, Argentina
Published by arrangement with John Wiley & Sons

Barred olivine (BO) chondrules are present in ordinary and carbonaceous chondrites. We focus on the bulk major and trace element abundance composition of BO chondrules from carbonaceous, unequilibrated ordinary, and Rumuruti chondrites. Their bulk Fe/(FeO + MgO) wt% content versus the FeO wt% in olivine was used to divide these objects into FeO-poor and FeO-rich BO chondrules. The trace element content of bulk BO chondrules reveals the absence of fractionation among the abundances of elements having different geochemical behavior (e.g. Yb and [La-Ce]). This points to the predominance of a cosmochemical (e.g. gas/liquid or gas/solid condensation) instead of a geochemical process determining their elemental abundances. In addition, their bulk trace element content provides evidence for the physicochemical conditions that prevailed in the solar nebula during their formation. In general, such nebular regions are governed by local redox variations coupled with overall falling temperatures. The bulk chemical composition of the studied BO objects (e.g., Mg/Si bulk) suggests a time scale in which FeO-poor BO chondrules formed first in a chondrule-forming region rich in refractory trace elements. The progressive removal of refractory phases (e.g., hibonite, fassaite, melilite) led to a nebular reservoir depleted in the very refractory elements (e.g., Zr and Y) in which the rare earth elements (REEs) tend to reach equilibrium with the chondritic reservoir. From such a reservoir, the FeO-rich BO chondrules could have formed and were subsequently processed by metasomatic exchange reactions that equilibrated their moderately volatile V and Cr around chondritic values. The observed chemical variations are only possible if the studied BO chondrules behave as open systems exchanging elements with the cooling vapor. The inferred local redox variations coupled with overall falling temperatures could have taken place during the evolution of a single heterogeneous nebular reservoir in which Fe-poor and FeO-rich BO chondrules formed.