The Abundances of F, Cl, and H2O in 4Vesta from Eucrites

The abundance and distribution of magmatic volatiles (i.e., H, C, N, F, S, and Cl) within the silicate portion of a differentiated planetary body has important consequences on its thermochemical evolution. However, the abundances of magmatic volatiles within differentiated bodies are difficult to quantify, and they are often depleted by varying degrees relative to CI chondrites. The mechanisms of depletion are not well constrained and could relate to intrinsic volatile depletion of the building blocks that formed the bodies, high temperature processes that result from accretion, post-accretion loss through parent body geological processes and large-scale impacts, and/or redistribution within a parent body through processes like core formation [1–4]. In the present study, we aim to constrain the abundances of F, Cl, and H2O in eucrites to better understand the magnitude of volatile depletion on 4Vesta. To accomplish this objective, we report electron microprobe analyses of apatite from seven unbrecciated, non-cumulate eucrites (i.e., CMS 04049,GRA 98098, LEW 88010, MAC 02522, MAC 041169,QUE 94484, and QUE 97053) and two monomict, non-cumulate eucrites (i.e., Berthoud and Stannern). In combination with previously published data on eucrite-hosted apatite, we determine Cl/F and H2O/F ratios in bulk rock eucrites through the application of apatite-based melt hygrometry and chlorometry [e.g., 5–7].Additionally, we estimate the bulk rock abundances of F in six non-cumulate eucrites (i.e., GRA 98098, MAC041169, PCA 91078, QUE 97053, Stannern, and Berthoud), which we combine with previously published bulk rock F data on non-cumulate eucrites[8] to constrain the abundances of F, Cl, and H2O in 4Vesta using appropriately paired volatile/refractory element ratios for F, followed by Cl/F and H2O/F ratios for Cl and H2O, respectively.