1. An Historical Perspective on Fission-Track Thermochronology

This chapter reviews the background, beginnings and early development of fission-track (FT) thermochronology. In the 1930s, it was discovered that uranium would break into two lighter products when bombarded with neutrons and, subsequently, that uranium was capable of natural, spontaneous fission. The fission process produced damage tracks in solid-state detectors, which could be revealed by chemical etching and observed by electron and, later, by optical microscopy. Fleischer, Price and Walker at the General Electric R&D laboratories developed diverse track-etching procedures, estimates of track registration and stability in different materials, track formation models, uranium determination in terrestrial, lunar and meteorite samples, neutron dosimetry and mineral dating using ²³⁸U spontaneous fission. Application to dating of natural and man-made glass was frustrated by low-uranium content and relative ease of track fading (annealing). In the 1970s–1980s, most FT analyses used apatite, zircon and titanite (sphene) to date tephra and acid intrusive rocks with the recognition of differing sensitivities of track annealing in each mineral. Studies in the Alps showed apatite with its greater susceptibility to annealing could provide estimates of the timing and rate of exhumation. The landmark 1980 Pisa FT Workshop highlighted problems with FT system calibration and emphasised the value of annealing in apatite to reveal thermal history. System calibration eventually reached a consensus agreement in 1988 at the Besançon FT Workshop with the majority of analysts adopting the zeta comparative approach. Multiple laboratory and borehole studies have determined the conditions for track annealing in apatite leading to widespread applications in exhumation, sedimentary basin, hydrocarbon exploration and other areas.