The Vaca Muerta mesosiderite: The path under which Fe-Ni alloy C phases could have formed

The combined SEM and TEM studies on the metal (Fe-Ni alloy +/- C) portion of the Vaca Muerta mesosiderite reveal structural and compositional evidence at micro to nanoscale, which sheds light on the solidification of taenite + graphite as a cement, and later solid-state precipitation process for the kamacite formation as grain boundary allotriomorph. Besides, it is proposed that the graphite veinlets formed through a complex partial melting process followed by a solidification toward the final eutectic transient coupled with the solid-state precipitation and later decomposition ordering of taenite. The presence of defects and taenite in graphite signal formation in a liquid environment. The delta 13C values of graphite in the graphite-rich areas (e.g., ranging from -0.8 +/- 1.7 parts per thousand to +15.3 +/- 2.5 parts per thousand) suggest a short-circuit diffusion path for C isotope fractionation.