Graphite crystallinity and thermal record in Campo del Cielo IAB iron meteorite: A window into impact processing on a chondritic bodyOPEN ACCESS 

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Xiao Tian Deng, Hong Yi Chen, Yang Li, Jin Yu Zhang, Lan Fang Xie, Si Zhe Zhao, Zhuang Guo, Chen Li, Kai Rui Tai

MAPS, Version of Record online: 24 January 2026

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“The Campo del Cielo iron meteorite (IAB-MG) provides a unique window into early solar system processes, particularly the formation and evolution of carbon phases in non-magmatic iron meteorites. In this study, we conducted a systematic nanostructural investigation of three distinct graphite occurrences—cliftonite (type I), interstitial graphite (type II), and silicate-associated graphite (type III)—within a single meteorite sample. Using a multi-technique approach, including scanning and transmission electron microscopy, Raman spectroscopy, X-ray diffraction, and electron probe microanalysis, we characterized their crystallographic properties, crystallinity, crystallite size, and crystallization temperatures. Our results 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 I and II show comparable nanostructural features and lower crystallization temperatures (~991°C and ~1013°C, respectively). These differences reflect a crystallization sequence from silicate-associated with metal-encapsulated graphite, consistent with formation in impact-generated metallic melt pools. The absence of diamond or diaphite structures indicates peak shock pressures below ~100 GPa. Combined with mineral chemistry data indicating a reduced, magnesium-rich silicate assemblage akin to CR chondrites, our findings support an origin via impact melting on a partially differentiated, CR-like parent body. This work underscores the role of localized, shock-induced thermal processing in shaping the carbon inventory of primitive planetary bodies and provides a mineralogical framework for understanding the complex formation history of IAB iron meteorites.”

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