^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.

¹Isabelle S. Mattia,¹Matthew J. Genge,²Martin D. Suttle
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70105]
¹Department of Earth Sciences, Imperial College London, London, UK
²School of Physical Sciences, The Open University, Milton Keynes, UK
Published by arrangement with John Wiley & Sons

Fossil micrometeorites (MMs) recovered from lithified sedimentary rocks, particularlyiron-rich (I-type) cosmic spherules (CSs) provide valuable insights into past dust-forming events.Their abundances, when combined with estimates of local sedimentation rates can be used toreconstruct the flux of extraterrestrial dust. However, their preservation in the geological recordis highly susceptible to postdepositional diagenetic processes, complicating their quantificationand past flux calculations. This study investigated lenticular calcitic concretions as potential sitesof enhanced preservation of fossil MMs. A total of 17–18 I-types (but no silicate dominatedspherules, S-types) were recovered from Cenomanian sediments within the Cretaceous ChalkSupergroup at Lulworth Cove, England. The I-types, identified by optical and SEM–EDXanalyses, exhibited typical dendritic textures and varying degrees of alteration, including mottledsurfaces and loss of Ni and Cr by leaching. Calcitic concretions yielded a comparableconcentration of I-types to the surrounding hosting marl, but due to the added carbonatecementation during their growth, preservation per original sediment volume was shown to beenhanced (potentially by up to ~60%). Calcitic concretions can therefore act asmicroenvironments that enhance fossil MM preservation by limiting complete dissolution andloss of I-types. To constrain possible diagenetic effects on fossil MM quantification, futurestudies should compare cosmic dust yields across multiple sites exposing the same targetedsedimentary horizon.