Cooling rates for lunar samples determined with a diffusion model for phosphide exsolutionA numerical model for diffusion-controlled phase growth has been applied to the exsolution of phosphide lamellae in lunar metal grains. Computer simulations reproduce observed composition profiles, and reveal the influence of cooling rate on dimensional and compositional parameters of phosphide and metal. At lower cooling rates, phosphide lamellae are larger and the concentration of P in the metal host close to the interface is lower. Cooling rates inferred for Apollo 16 samples, based on compositions and dimensions of the phosphide-metal grains, are mostly in the range 1-100 C/day. These rates correspond to burial depths of 5-0.5 m for melt rocks and 3-0.3 m for breccias. This is in good agreement with thicknesses of lunar cooling units determined by other techniques.
Document ID
19780057745
Acquisition Source
Legacy CDMS
Document Type
Conference Proceedings
Authors
Hewins, R. H. (Rutgers University New Brunswick, N.J., United States)
Goldstein, J. I. (Lehigh University Bethlehem, Pa., United States)