STATISTICAL PROPERTIES OF SEMI-TRACKS IN FISSION-TRACK ANALYSIS

The lengths of fission tracks in an apatite crystal reflect its therma l history. This article is concerned with the estimation of thermal hi story parameters from semi-track measurements, i.e. the remaining part s of tracks that have intersected a polished prismatic surface. We pre sent formulae and calculations for semi-tracks corresponding to those for projected tracks given in Laslett et al. (1994). For semi-tracks, the formulae are simpler and the potential information is greater. For thermal histories described by two parameters mu(1) and p, correspond ing to the maximum palcotemperature and the timing of uplift and erosi on or cooling, we study what parameter values can be estimated with re asonable precision, what sample sizes are necessary, how useful are me asurements of angles (in addition to lengths), and how the estimates c ompare with those from confined tracks and from projected tracks. Qual itatively, the results for semi- tracks mimic those for projected trac ks: precise estimates can be obtained when p is large, corresponding t o recent cooling, and when mu(1) is small, corresponding to a high max imum paleotemperature; and measurement of angles improves the estimate of mu(1) but makes only a small improvement to the estimate of p. Qua ntitatively, there is a substantial gain in precision from measuring s emi-tracks rather than projected tracks. Copyright (C) 1996 Elsevier S cience Ltd