^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.