POSITIONING THE TITANITE FISSION-TRACK PARTIAL ANNEALING ZONE

As part of the KTB (Kontinentale Tiefbohrung) programme in Germany, ti tanite (sphene) fission-track data were acquired for samples to a dept h of 9000 m, where the host rock temperature is similar to 265 degrees C. At this depth, age and confined track length information suggest t hat the partial annealing zone for the fission tracks in titanite was not reached. By reconstructing the thermal history and 'backstacking' of an uplifted partial annealing zone, it is suggested that the in sit u partial annealing zone is likely to be found in the region 265-310 d egrees C. This value is more precise than previous estimates of the ti tanite partial annealing zone, and it is also higher than previous est imates. Microprobe analysis indicates that the chemical composition of the titanites is rather homogeneous throughout the whole drilled sect ion. (C) 1998 Elsevier Science B.V. All rights reserved.