What’s up? Preservation of gravitational direction in the Larkman Nunatak 06299 LL impact melt breccia

摘要: Abstract– Larkman Nunatak (LAR) 06299 is a vesicular LL chondrite impact melt breccia that cooled rapidly (0.1–0.3 °C s−1) during crystallization. Ar-Ar data from the literature indicate event formed this rock occurred approximately 1 Ga ago. About 30 vol% of meteorite consists matrix containing faceted and intergrown mafic silicate grains (mainly 4–11 μm size olivine phenocrysts) partially to completely surrounded by 2–20 μm patches plagioclase. Suspended in are 30–370 μm ellipsoidal spheroidal metal-sulfide nodules (several hundred per thin section), many connected 8–600 μm vesicles. Most contain large oblate metallic Fe-Ni bleb at one end nodule. For 90% nodules, metal blebs aligned on same side nodules; for 80% adjacent vesicles, vesicles attached opposite blebs. themselves flattened direction perpendicular long axis nodule/vesicle. These features result alignment gravitational field parent asteroid, making LAR 06299 first known direction. Using reasonable estimates cooling rate, viscosity melt, asteroid density, as well observed sizes constituent phases LAR 06299, we obtain lower limit 1.5 km radius body. The body was probably substantially larger.