Zoë E. Wilbur¹, Timothy J. McCoy², Catherine M. Corrigan², Jessica J. Barnes¹, Sierra V. Brown³, Arya Udry⁴
Meteoritics & Planetary Science (in Press) Open Access
Link to Article [https://doi.org/10.1111/maps.14220]
¹Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
²Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, District of
Columbia, USA
³Million Concepts, LLC, Louisville, Kentucky, USA
⁴University of Nevada, Las Vegas, Nevada, USA
Published by arrangement with John Wiley & Sons

Enstatite meteorites, both aubrites and enstatite chondrites, formed under exceptionally reducing conditions, similar to the planet Mercury. Despite being reduced, the MESSENGER mission showed that the surface of Mercury is more enriched in volatiles (e.g., S, Na, K, Cl) than previously thought. To better understand the mineral hosts of these volatiles and how they formed, this work examines the chemistry and petrographic settings of a rare, K-bearing sulfide called djerfisherite within enstatite chondrites and aubrites. The petrographic settings of djerfisherite within aubrites suggest this critical host of Cl formed after both the crystallization of troilite and exsolution of daubréelite. Djerfisherite is commonly observed as a rim on other sulfides and in contact with metal. We present an alteration model for djerfisherite formation in aubrite meteorites, whereby troilite and Fe-Ni metal are altered through anhydrous, alkali- and Cl-rich fluid metasomatism on the aubrite parent body to produce secondary djerfisherite. Moreover, we observe a loss of volatiles in djerfisherite within impact melted regions of the Miller Range 07139 EH3 chondrite and the Bishopville aubrite and explore the potential for impact devolatilization changes to sulfide chemistry on other reduced bodies in the Solar System. Vapor or fluid phase interactions are likely important in the formation of volatile-rich phases in reduced systems. While most Na and K on the mercurian surface is expected to be hosted in feldspar, djerfisherite is likely a minor, but critical, reservoir for K, Na, and Cl. Djerfisherite present on reduced bodies, such as Mercury, may represent sulfides formed via late-stage, primary metasomatism.

Akimasa Suzumura^1,3, Noriyuki Kawasaki², Hisayoshi Yurimoto², Shoichi Itoh¹
Meteoritics & Planetary Science (in Press) Open Access
Link to Article [https://doi.org/10.1111/maps.14222]
¹Department of Earth and Planetary Sciences, Kyoto University, Kyoto, Japan
²Department of Natural History Sciences, Hokkaido University, Sapporo, Japan
³Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan
Published by arrangement with John Wiley & Sons

A melilite-rich, compact type A Ca-Al-rich inclusion (CAI), KU-N-02, from the reduced CV3 chondrite Northwest Africa 7865, is mantled by an åkermanite-poor layer. We carried out a combined study of petrographic observations and in situ O and Al–Mg isotopic measurements for KU-N-02. The core shows a typical texture of igneous compact type A CAIs. The mantle consists of spinel, åkermanite-poor melilite, and perovskite. Individual mantle melilite crystals show reverse zoning toward the crystal grain boundary, in contrast to core melilite crystals showing normal zoning. The O isotopic compositions of the minerals in KU-N-02 plot along the carbonaceous chondrite anhydrous mineral line on a three O-isotope diagram. The mantle and core spinel crystals are uniformly ¹⁶O-rich (Δ¹⁷O ~ −23‰). The mantle melilite crystals exhibit variable O isotopic compositions ranging between Δ¹⁷O ~ −2‰ and −9‰, in contrast to the uniformly ¹⁶O-poor (Δ¹⁷O ~ −2‰) core melilite. The mantle melilite crystals also exhibit variable δ²⁵Mg values (δ²⁵Mg_DSM-3 ~ −2‰ to +3‰) compared with the nearly constant δ²⁵Mg values of the core melilite (δ²⁵Mg_DSM-3 ~ +2‰). The mantle minerals are likely to have formed by condensation from the solar nebular gas after core formation. The Al–Mg mineral isochrons of the core and mantle give initial ²⁶Al/²⁷Al ratios of (4.66 ± 0.15) × 10⁻⁵ and (4.74 ± 0.14) × 10⁻⁵, respectively. The age difference between the core and mantle formation is estimated to be within ~0.05 Myr, implying that both melting and condensation processes in the variable O isotopically solar nebular environments occurred within a short time during single CAI formation.