Abstract: Meteorite fusion crusts are formed during atmospheric entry and show different textural characteristics based on differences in entry velocity and structural changes in the atmosphere. Therefore, fusion crust study is important to understand atmospheric entry processes and atmospheric structure at that time. Many Antarctic meteorites have retained their original or complete fusion crust because of the region’s unique geographical and climatic conditions, so they are ideal samples for fusion crust research. An ordinary H5 chondrite (GRV 090196) from the Grove Mountains region (Antarctica) was investigated in this study. It has a complete molten fusion crust with some flow lines showing its flying direction. Thin sections showed two intact fusion crusts with thicknesses of 1.3 mm and 0.4 mm. Petrology and mineralogy showed that the first fusion crust (Ⅰ) could be divided into four structural layers (outside to inside). Layers 1 and 2 were melted completely and recrystallized to form porphyritic structures in a glassy matrix, but the morphology and chemical composition of olivine phenocrysts in these layers were very different. This indicates it experienced different atmospheric layers of various densities. In layer 3, partial melting was obvious and mineral residues were observed; crystals were rounded with some bubbles. Thermal metamorphism occurred in layer 4, appearing opaque and black under plane polarized light, with a darkening phenomenon that may be from fine iron precipitation. Its texture was similar to those inside the meteorite. The second fusion crust (Ⅱ) was divided into three layers (outside to inside). Silicates in layer 1 were partially melted and rich in metallic grains. Layers 2 and 3 were similar to layers 3 and 4 in fusion crustⅠ. We suggest that fusion crusts were caused by accumulation and can be used to judge the landing direction of a meteorite. The two glassy layers and olivine phenocrysts in fusion crustⅠas well as the recrystallized olivine phenocrysts indicate that fusion crust melt was moved along the meteorite body by air. The fusion crusts experienced two relatively denser atmosphere layers that formed two glassy layers, and fusion crustⅡwas located in the side of the front. Only a small amount of the molten material remained and formed a very thin glassy fusion crust.

Key words: ordinary chondrite, fusion crust, accumulation cause, Antarctica