^1,2,3Xiao Tian Deng,^1,2Hong Yi Chen,³Yang Li,^1,2Jin Yu Zhang,^1,2Lan Fang Xie,³Si Zhe Zhao,⁴Zhuang Guo,⁵Chen Li⁶Kai Rui Tai
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70085]
¹Institution of Meteorites and Planetary Materials Research, Key Laboratory of Planetary Geological Evolution of Guangxi Provincial Universities, Guilin University of Technology, Guilin, China
²Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, Guilin University of Technology, Guilin, China
³Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
⁴Department of Geology, Northwest University, Xi’an, China
⁵School of Engineering, Yunnan University, Kunming, China
⁶College of Earth and Planetary Sciences, Chengdu University of Technology, Chengdu, China
Published by arrangement with John Wiley & Sons

The Campo del Cielo iron meteorite (IAB-MG) provides a unique window into earlysolar system processes, particularly the formation and evolution of carbon phases innon-magmatic iron meteorites. In this study, we conducted a systematic nanostructuralinvestigation of three distinct graphite occurrences—cliftonite (type I), interstitial graphite(type II), and silicate-associated graphite (type III)—within a single meteorite sample. Using amulti-technique approach, including scanning and transmission electron microscopy, Ramanspectroscopy, X-ray diffraction, and electron probe microanalysis, we characterized theircrystallographic properties, crystallinity, crystallite size, and crystallization temperatures. Ourresults reveal that type III graphite exhibits the highest crystallinity and largest crystallite size(average La = 287.4 nm), with a peak crystallization temperature of 1112°C, while types Iand II show comparable nanostructural features and lower crystallization temperatures(991°C and 1013°C, respectively). These differences reflect a crystallization sequence fromsilicate-associated with metal-encapsulated graphite, consistent with formation inimpact-generated metallic melt pools. The absence of diamond or diaphite structures indicatespeak shock pressures below 100 GPa. Combined with mineral chemistry data indicating areduced, magnesium-rich silicate assemblage akin to CR chondrites, our findings support anorigin via impact melting on a partially differentiated, CR-like parent body. This workunderscores the role of localized, shock-induced thermal processing in shaping the carboninventory of primitive planetary bodies and provides a mineralogical framework forunderstanding the complex formation history of IAB iron meteorites.