Petrography and Metallographic Cooling Rate of H-chondrite Impact Melt

Introduction: Impact melts resulting from craterproducing impacts on asteroids can be used to understand the collisional evolution of our solar system. Part of that analysis includes an assessment of the cooling rates of the impact melts and/or the locations where the melts are deposited. In this study, we examined LAP 04751 [1], which is an impact melt breccia that came from the H-chondrite parent body. Petrography: Thin section LAP 04751,6 is composed of 54% impact melt (7.3 % in quenched zones around clasts) and 46% surviving clasts. A detailed point count (1742 pts with a spacing of 100 μm) of the melt indicates the silicate matrix (66.9% of the melt) entrains orbicular metal and sulfide (16.7% of the melt; Fig. 1) and small (≤310 μm) silicate xenocrysts and xenoliths (12.7% of melt) that also survived the impact. Fractures and holes (3.7%) are randomly distributed through the melt.