FISSION-TRACK ANNEALING SYSTEMATICS IN APATITE WITH GEOLOGICAL APPLICATIONS (ORGAN MOUNTAINS, NEW MEXICO, RIO GRANDE RIFT, UPLIFT EROSION)

Published data from laboratory fission-track annealing experiments are used to evaluate the empirical expressions that relate fission-track annealing, time, and temperature that have been proposed in the literature. Temperature fluctuations that commonly occur during nominally isothermal annealing experiments have been ignored in previous statistical analyses of the empirical functions; the effect of these temperature fluctuations on the evaluation of the equations is considered in detail in this study. The results of this work indicate that the published data cannot be used to study the annealing of the fission tracks in geological situations due to the uncertainties introduced into the empirical coefficients by the temperature variations.; Consequently, the annealing of fission tracks in apatite is studied using new experimental techniques that minimize temperature fluctuations during isothermal annealing experiments. The new data are used to determine the coefficients for the empirical expressions that describe the time and temperature behavior of fission-track annealing. Isothermal annealing of fisson tracks that have been previously annealed under known, nonisothermal temperature conditions is also examined. The results from these experiments show that the rate of fission-track annealing decreases as the degree of pre-annealing increases. This observation indicates that the empirical time-temperature equations for track annealing need to be modified to take this rate change into account if they are to be used to aid in the interpretation of fission-track ages in areas having complex thermal histories.; Fission-track ages are utilized in two geological applications. First, apatite, sphene, and zircon fission-track ages are used to unravel the thermal history of the Organ batholith in south-central New Mexico. Second, apatite fission-track ages are used to describe the late Cretaceous to middle Miocene uplift and erosional history of the northern Rio Grande rift, New Mexico.