Rb-Sr age of the Shergotty achondrite and implications for metamorphic resetting of isochron ages

摘要: Abstract An internal Rb-Sr isochron for the Shergotty achondrite yields extremely young age of 165 ± 11 Myr and high initial 87Sr/86Sr = 0.72260 0.00012. This is interpreted as resulting from resetting system by shock event in which plagioclase was converted to maskelynite. A model quantifying ‘degree resetting’ ages introduced order discuss context discordant obtained K-Ar Sm-Nd methods. It possible consider different apparent within a single conceptual framework based on diffusive transport elements out between mineral grains. Some generalizations about relative resistance various types are made semi-empirical treatment factors governing activation energies diffusion Ar, Sr Nd. Constraints put burial depth cooling time required reset radiometric measured Shergotty. The scenario most consistent with all constraints, including particular rates Nd, is: 1. (1) crystallized melt 650 ago. 2. (ii) parent object involved an energetic collision Our sample heated ~300–400°C after it remained buried under hundreds meters overburden cooled ~ 104 yr. 3. (iii) exposed cosmic rays small ~2