Petrology and mineralogy of mesosiderite Northwest Africa 12949: Implications for geological history on its parent body

1,2Zilong Wang,1Wei Tian
Meteoritics & Planetary Science (in Press) Link to Article []
1The Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing, China
2The Key Laboratory of Paleomagnetism and Tectonic Reconstruction of MNR, Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing, China
Published by arrangement with John Wiley & Sons

Mesosiderites are breccias composed of roughly equal parts of metal phases and silicate clasts. However, the parent body and formation process of mesosiderites remain enigmatic. Northwest Africa (NWA) 12949 is a newly found mesosiderite belonging to type 2A. One type of ultramafic clasts and four types of mafic clasts (gabbroic, poikilitic, subophitic, and cataclastic), compositionally consistent with diogenites and eucrites, have been identified in NWA 12949. However, these clasts have undergone different thermal histories, with cooling rates varying from ~0.0044 °C year−1 to a few °C h−1, and equilibrium temperatures varying from ~880 to 910 °C to ~1000 to 1100 °C. All the lithic clasts have undergone redox reactions during extensive metamorphism, forming excess troilite, chromite, merrillite, tridymite, and pyroxene with lower Fe/Mg and Fe/Mn. The petrology and mineralogy of NWA 12949 support a formation scenario involving two major impact events, and a candidate parent body of 4 Vesta.


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