Record of S-rich vapors on asteroid 4 Vesta: Sulfurization in the Northwest Africa 2339 eucrite Ai-Cheng Zhang a,b,⇑ , Ru-Cheng Wang a , Wei-Biao Hsu c , Rainer Bartoschewitz d a State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China b Department of Natural History Sciences, Hokkaido University, Sapporo 060-0810, Japan c Laboratory of Astrochemical and Planetary Science, Purple Mountain Observatory, Nanjing 210008, China d Meteorite Laboratory, Gifhorn D-38518, Germany Received 25 October 2012; accepted in revised form 27 January 2013; Available online 9 February 2013 Abstract In the Northwest Africa (NWA) 2339 eucrite, a few high-Fe pigeonite fragments were partially replaced by fine-grained troilite, Mg-rich augite, silica, with minor ilmenite and Mg-rich ferrosilite. The relict pigeonite has distinctly lower Fe/Mn values (17–18) than those (30) of augite and Mg-rich ferrosilite in the fine-grained replacement textures and other eucritic pyroxenes in NWA 2339. The few plagioclase grains associated with these Fe-rich pigeonite fragments contain high albite components (Ab 17–31 ). Similar replacement textures are also present in a lithic clast consisting of pyroxene and Na-rich pla- gioclase (Ab 20–25 ). In this lithic clast, high-Fe subcalcic augite was replaced by troilite, Mg-rich hedenbergite, silica, and minor ilmenite whereas Mg-rich pigeonite remains intact. Troilite also occurs as tiny inclusions in porous regions of plagioclase. Moreover, the porous regions of plagioclase are enriched in Si and depleted in Al, Ca, and Na, compared to relict plagioclase. These textures indicate that the formation of troilite-rich mineral assemblages is related to the reaction between FeSiO 3 com- ponent in pyroxene and S-rich vapors; whereas, the formation of tiny troilite in porous regions of plagioclase is related to the reaction between Fe 2+ in plagioclase and S-rich vapors. X-ray mapping results reveal that during sulfurization of pyroxene and plagioclase, lithophile elements Mn, Al, Ca, Na, and Mg were removed to various extents, very likely by the S-rich vapors. Based on our observations, the S-rich vapors could be dry S–O–P vapors, which most likely have been formed by volatilization of pre-existing S,P-bearing materials due to impact heating on the surface of asteroid 4 Vesta. Ó 2013 Elsevier Ltd. All rights reserved. 1. INTRODUCTION Similar reflectance spectroscopic features between the surface of 4 Vesta and howardite–eucrite–diogenite (HED) meteorites imply that the former could be the parent body of HED meteorites (Binzel and Xu, 1993; McSween et al., 2011; Russell et al., 2012). Short-lived and long-lived radiometric ages of HED meteorites indicate that Vesta could have completed its accretion and differentiation, and even thermal metamorphism very early (4.5 Ga ago; Coradini et al., 2011 and references therein). Thus, Vesta is considered to be a remnant intact protoplanet (Russell et al., 2012), and its early history is very important for con- straining the internal evolution of protoplanets. However, to understand the early history of Vesta, we must identify possible effects of post-crystallization processes (especially exogenous processes) that could have taken place on Vesta, such as shock metamorphism and fluid-rock interaction. Shock metamorphism could be the most important pro- cess modifying the surface morphology of Vesta (e.g., Mar- chi et al., 2012). This process also results in fragmentation and brecciation of rocks on the surface of Vesta. However, the modification by impact events of minerals and the chemistry of surface rocks (e.g., HED meteorites) on Vesta has not been studied in detail. The few descriptions about 0016-7037/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.gca.2013.01.036 ⇑ Corresponding author at: State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China. E-mail address: aczhang@nju.edu.cn (A.-C. Zhang). www.elsevier.com/locate/gca Available online at www.sciencedirect.com Geochimica et Cosmochimica Acta 109 (2013) 1–13