^1,2Laura Noel García,¹María Eugenia Varela,³Shyh-Lung Hwang,⁴Pouyan Shen,⁵Raúl Bolmaro,⁵Martina Ávalos
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13911]
¹Instituto de Ciencias Astronómicas, de la Tierra y del Espacio (ICATE), Universidad Nacional de San Juan, CONICET, J5402DSP San Juan, Argentina
²Instituto de Mecánica Aplicada, Universidad Nacional de San Juan, J5400ARL San Juan, Argentina
³Department of Materials Science and Engineering, National Dong Hwa University, 974 Hualien, Taiwan, ROC
⁴Department of Materials and Optoelectronic Science, National Sun Yat-sen University, 804 Kaohsiung, Taiwan, ROC
⁵Instituto de Física Rosario (IFIR), Universidad Nacional de Rosario, CONICET, S2000EKF Rosario, Argentina
Published by arrangement with John Wiley & Sons

Meteorites carry information about the most common processes that have been active in the early solar system. In particular, mesosiderites are meteorites with a structure considered to be composed of equal parts of iron–nickel metal and silicates. A natural delimitation in the study of such complex systems is the discrimination of the iron–nickel metallic and silicate domains. In this work, we focus on the metallic phases of the Mincy mesosiderite, a specimen available at the Instituto de Ciencias Astronómicas, de la Tierray y del Espacio repository. In Mincy, the metallic phases are iron–nickel–carbon alloys that are distributed forming metallic lumps or pebbles (referred to as metallic nodules in the article) in which kamacite and taenite are present, and taenite is found both at the kamacite/silicate interface and surrounded by kamacite, that is, isolated from the silicates. We made use of the electron backscattered diffraction technique to determine the crystallographic orientation relationships along the taenite/kamacite boundaries as well as for characterizing the (hkl)-specific grain boundaries regarding the underlying tilt, twist, or twinning mechanism to assist the interpretation of the phase transformations and mechanisms that could explain the formation of these metallic nodules. From the results, each of the metallic nodules has a unique temperature–pressure history and kinetics to undergo phase transformations (mainly partial melting, heterogeneous nucleation-controlled solidification, and possible evaporation–condensation) as well as liquid-phase sintering and recrystallization in its own way.

¹Aryavart Anand,¹Pascal M. Kruttasch,¹Klaus Mezger
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13916]
¹Institut für Geologie, Universität Bern, Baltzerstrasse 1+3, 3012 Bern, Switzerland
Published by arrangement with John Wiley & Sons

The meteorite Erg Chech (EC) 002 is the oldest felsic igneous rock from the solar system analyzed to date and provides a unique opportunity to study the formation of felsic crusts on differentiated protoplanets immediately after metal–silicate equilibration or core formation. The extinct ⁵³Mn-⁵³Cr chronometer provides chronological constraints on the formation of EC 002 by applying the isochron approach using chromite, metal–silicate–sulfide, and whole-rock fractions as well as “leachates” obtained by sequential digestion of a bulk sample. Assuming a chondritic evolution of its parent body, a ⁵³Cr/⁵²Cr model age is also obtained from the chromite fraction. The ⁵³Mn-⁵³Cr isochron age of 1.73 ± 0.96 Ma (anchored to D’Orbigny angrite) and the chromite model age constrained between $$ {1.46}_{-0.68}^{+0.78} $$ and $$ {2.18}_{-1.06}^{+1.32} $$ Ma after the formation of calcium-aluminium-rich inclusions (CAIs) agree with the ²⁶Al-²⁶Mg ages (anchored to CAIs) reported in previous studies. This indicates rapid cooling of EC 002 that allowed near-contemporaneous closure of multiple isotope systems. Additionally, excess in the neutron-rich ⁵⁴Cr (nucleosynthetic anomalies) combined with mass-independent isotope variations of ¹⁷O provides genealogical constraints on the accretion region of the EC 002 parent body. The ⁵⁴Cr and ¹⁷O isotope compositions of EC 002 confirm its origin in the “noncarbonaceous” reservoir and overlap with the vestoid material Northwest Africa 12217 and anomalous eucrite Elephant Moraine 92023. This indicates a common feeding zone during accretion in the protoplanetary disk between the source of EC 002 and vestoids. The enigmatic origin of iron meteorites remains still unresolved as EC 002, which is more like a differentiated crust, has an isotope composition that does not match known iron meteorite groups that were once planetesimal cores.