A borehole investigation of zircon radiation damage annealing

This contribution reports Raman radiation damage measurements of zircons from the Kontinentale Tiefbohrung, on the western border of the Bohemian Massif. The mean wavenumbers (omega(3)) and widths (Gamma(3)) of the nu(3)(SiO4) Raman band are constant down to 3 km, decrease (omega(3)) resp. increase (Gamma(3)) between 3 and 5 km, and are again constant between 5 and 7 km. Uniform high Gamma(3) values associated with omega(3) values close to those of undamaged zircon between 5 and 7 km are interpreted as due to residual damage predating the exhumation of the Bohemian Massif. A superimposed post-exhumation signal indicates full damage retention down to 3 km depth, partial annealing between 3 and 5 km, and zero retention at greater depth. An attempt to calculate radiation damage ages gives results of a meaningful order of magnitude but also exposes difficulties associated with dating basement samples with complex damage accumulation and annealing histories.