Annealing of shocked quartz during atmospheric re-entry

Abstract

The Chicxulub impact launched shocked quartz grains on ballistic trajectories outside the atmosphere, thus enabling their global dissemination. The shocked grains heated up during atmospheric re-entry and the maximum temperature reached was related to their size, velocity and re-entry angle. The extreme heating of some shocked quartz grains is likely to have resulted in the destruction of their planar deformation features (PDFs). A significant negative correlation exists between the palaeodistance from Chicxulub of a given K/T boundary locality and the size of the largest shocked quartz crystal found at that locality. The re-entry annealing process can explain this correlation. The largest shocked quartz grain at a given locality followed the shallowest available trajectory and survived re-entry without being thermally annealed. Larger crystals and those on steeper trajectories exceeded the annealing point and lost their PDFs.