Morphology and Cooling Rates of FeNi Metal–Sulfide Eutectic Blobs

Abstract

The metal-troilite blobs in the Yanzhuang shock-produced melt can be divided into three types: (i) blobs with dendritic texture, (ii) blobs with cellular texture, and (iii) irregular cellular blobs. All they are with textures of FeNi–FeS eutectic intergrowth aggregates. Based on the dendrite arm spacing or cell widths of blobs, the calculated cooling rates in melt pockets are 0.8–67.8 ℃/s, while those in melt veins are 103–2935 ℃/s. It was revealed that the local shock-induced melting took place at the surface of Yanzhuang parent body to form melt pockets of 4–35 mm in size. The melt veins formed by filling the fractures of shock melt are only 1–5 mm in width. This indicates that the Yanzhuang meteorite had subjected extremely heavy impact and in-situ melting event, and experienced very complicated rapid cooling process.