¹Jingyou Chen, ²Ying Wang, ³Ai-Cheng Zhang, ²Shiyong Liao, ⁴Shaolin Li, ¹Sky Beard, ¹Meng-Hua Zhu
Journal of Geopyhsical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2023JE007954]
¹State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, China
²CAS Center for Excellence in Comparative Planetology, Purple Mountain Observatory, Nanjing, China
³State Key Laboratory for Mineral Deposits Research and School of Earth Science and Engineering, Nanjing University, Nanjing, China
⁴Astronomical Research Center, Shanghai Science & Technology Museum, Shanghai, China
Published by arrangement with John Wiley & Sons

Mesosiderites are thought to be created by a catastrophic impact that mixes the silicate crust with the metallic core of a differentiated asteroid(s). The metal-silicate mixing event greatly affects the subsequent geological evolution of the mesosiderite parent body. To gain a better understanding of this mixing event, we carried out studies on olivine alteration and merrillite Pb-Pb thermochronology in the Dong Ujimqin Qi mesosiderite. The primary olivine in this meteorite has been altered through sulfidation reactions, leading to the formation of troilite-orthopyroxene intergrowths. This alteration likely took place during metal-silicate mixing, as the mixing environment can provide favorable chemical and thermal conditions for this reaction. Phosphate-chromite veins crosscutting the troilite-orthopyroxene intergrowths indicate a secondary alteration process likely induced by subsequent impacts. Additionally, the metal-silicate mixing event likely contributed to the occurrence of abundant merrillites at the boundary between silicates and Fe-Ni metals, as supported by the distinctly depleted incompatible elements resulting from the redox reaction between metals and adjacent silicates. The ion microprobe analyses for these merrillites yielded a Pb-Pb age of 4,064 ± 120 Ma, which is interpreted as the record of the Pb isotopic closure of merrillite during prolonged cooling associated with the deep burial. Our two-stage cooling model suggests that the mesosiderite parent body’s burial potentially started around 4.52 Ga, which is consistent with the Sm-Nd, Ar-Ar, and Pb-Pb thermochronological records in mesosiderites.

¹D. Paul,¹S. Dhoundiyal,¹M. Aranha,¹A. Porwal,²G. Thangjam
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115865]
¹CSRE Department, IIT Bombay, Powai-400076, India
²School of Earth and Planetary Sciences, NISER, HBNI, Bhubaneswar 752050, India
Copyright Elsevier

Pyroxene chemistry estimated using a series of spectral parameters derived from Chandrayaan-I M3 data was used to divide the basalts of Mare Humorum into six compositional units. In order to understand the petrogenetic history of the Humorum basalts, first, the dominant pyroxene end-member composition in each unit is used to estimate the temperature of crystallization; and then crater counting is implemented using craters mapped from the high-resolution Kaguya Terrain Camera data to estimate the age of each unit. The spatial distributions of pyroxene composition and corresponding crystallization temperatures indicate that there is a difference in volcanic activity between the regions corresponding to Units 1–3 (Group I) and the regions corresponding to Units 4–6 (Group II). This observation is further reinforced by analyzing the variation of FeO and TiO2 content across the units. Hence two sources ilmenite-rich HCP and low ilmenite HCP correspond to two groups of basalts in the Humorum area. Furthermore, our new crater-counting analysis reveals that the magmatic activity probably continued until ca. 1.9 Ga in the Humorum basin. To the best of our knowledge, this younger age of volcanism has not been reported before.