Abstract
Previous inter-laboratory experiments on confined fission-track length measurements in apatite have consistently reported variation substantially in excess of statistical expectation. There are two primary causes for this variation: (1) differences in laboratory procedures and instrumentation, and (2) personal differences in perception and assessment between analysts. In this study, we narrow these elements down to two categories, etching procedure and analyst bias. We assembled a set of eight samples with induced tracks from four apatite varieties, initially irradiated between 2 and 43 years prior to etching. Two mounts were made containing aliquots of each sample to ensure identical etching conditions for all apatites on a mount. We employed two widely used etching protocols, 5.0 M HNO3 at 20 °C for 20 s and 5.5 M HNO3 at 21 °C for 20 s. Sets of track images were then captured by an automated system and exchanged between two analysts, so that measurements could be carried out on the same tracks and etch figures, in the same image data, allowing us to isolate and examine the effects of analyst bias. An additional 5 s of etching was then used to evaluate etching behavior at track tips. In total, 8391 confined fission-track length measurements were performed; along with 1480 etch figure length measurements. When the analysts evaluated each other’s track selections within the same images for suitability for measurement, the average rejection rate was ∼14%. For tracks judged as suitable by both analysts, measurements of 2D and 3D length, dip, and c-axis angle were in excellent agreement, with slightly less dispersion when using the 5.5 M etch. Lengths were shorter in the 5.0 M etched mount than the 5.5 M etched one, which we interpret to be caused by more prevalent under-etching in the former, at least for some apatite compositions. After an additional 5 s of etching, 5.0 M tracks saw greater lengthening and more reduction in dispersion than 5.5 M tracks, additional evidence that they were more likely to be under-etched after the initial etching step. Systematic differences between analysts were minimal, with the main exception being likelihood of observing tracks near perpendicular to the crystallographic c axis, which may reflect different use of transmitted vs. reflected light when scanning for tracks. Etch figure measurements were more consistent between analysts for the 5.5 M etch, though one apatite variety showed high dispersion for both. Within a given etching protocol, each sample reflected a decrease of mean track length with time since irradiation, giving evidence of 0.2–0.3 μm of annealing over year to decade timescales.
Acknowledgments and Funding
This research was supported by the Geology Foundation of the Jackson School of Geosciences and the School of Earth Sciences at the University of Melbourne. We thank R. Jonckheere and E. Sobel for thorough and helpful reviews, which improved the quality of this work.
References cited
Barbarand, J., Carter, A., Wood, I., and Hurford, T. (2003a) Compositional and structural control of fission-track annealing in apatite. Chemical Geology, 198(1), 107–137.10.1016/S0009-2541(02)00424-2Search in Google Scholar
Barbarand, J., Hurford, T., and Carter, A. (2003b) Variation in apatite fission-track length measurement: Implications for thermal history modelling. Chemical Geology, 198(1), 77–106.10.1016/S0009-2541(02)00423-0Search in Google Scholar
Belton, D.X. (2006) The low-temperature thermochronology of cratonic regions. University of Melbourne, Ph.D. thesis, 306 pages.Search in Google Scholar
Bhandari, N., Bhat, S.G., Lal, D., Rajagopalan, G., Tamhane, A.S., and Venkatavaradan, V. S. (1971) Fission fragment tracks in apatite: recordable track lengths. Earth and Planetary Science Letters, 13, 191–199.10.1016/0012-821X(71)90123-3Search in Google Scholar
Carlson, W.D., Donelick, R.A., and Ketcham, R.A. (1999) Variability of apatite fission-track annealing kinetics: I. Experimental results. American Mineralogist, 84, 1213–1223.10.2138/am-1999-0901Search in Google Scholar
Donelick, R.A., and Miller, D.S. (1991) Enhanced tint fission track densities in low spontaneous track density apatites using 252 Cf-derived fission fragment tracks: A model and experimental observations. International Journal of Radiation Applications and Instrumentation, 18, 301–307.Search in Google Scholar
Donelick, R.A., Roden, M.K., Mooers, J.D., Carpenter, B.S., and Miller, D.S. (1990) Etchable length reduction of induced fission tracks in apatite at room temperature (≈23°C): Crystallographic orientation effects and “initial” mean lengths. International Journal of Radiation Applications and Instrumentation, Part, 17, 261–265.10.1016/1359-0189(90)90044-XSearch in Google Scholar
Donelick, R.A., Ketcham, R.A., and Carlson, W.D. (1999) Variability of apatite fission-track annealing kinetics: II. Crystallographic orientation effects. American Mineralogist, 84, 1224–1234.10.2138/am-1999-0902Search in Google Scholar
Donelick, R.A., O’Sullivan, P.B., and Ketcham, R.A. (2005) Apatite fission-track analysis. Reviews in Mineralogy & Geochemistry, 58, 49–94.10.1515/9781501509575-005Search in Google Scholar
Fleischer, R.L., Price, P.B., Walker, R.M., and Hubbard, E.L. (1964) Track registration in various solid-state nuclear track detectors. Physical Review, 133, 1443–1449.10.1103/PhysRev.133.A1443Search in Google Scholar
Fleischer, R.L., Price, P.B., and Woods, R.T. (1969) Nuclear-particle-track identification in inorganic solids. Physical Review, 188(2), 563–568.10.1103/PhysRev.188.563Search in Google Scholar
Gallagher, K. (2012) Transdimensional inverse thermal history modeling for quantitative thermochronology. Journal of Geophysical Research: Solid Earth, 177, B02408.10.1029/2011JB008825Search in Google Scholar
Gleadow, A.J.W., and Duddy, I.R. (1981) A natural long-term track annealing experiment for apatite. Nuclear Tracks, 5, 169–174.10.1016/0191-278X(81)90039-1Search in Google Scholar
Gleadow, A.J.W., and Lovering, J.F (1978) Fission track geochronology of King Island, Bass Strait, Australia: Relationship to Continental Rifting. Earth and Planetary Science Letters, 37, 429–437.10.1016/0012-821X(78)90058-4Search in Google Scholar
Gleadow, A.J.W., Duddy, I.R., Green, P.F., and Lovering, J.F. (1986) Confined fission track lengths in apatite: a diagnostic tool for thermal history analysis. Contributions to Mineralogy and Petrology, 94, 405–415.10.1007/BF00376334Search in Google Scholar
Gleadow, A.J.W., Gleadow, S.J., Belton, D.X., Kohn, B.P., Krochmal, M.S., and Brown, R.W. (2009) Coincidence mapping—a key strategy for the automatic counting of fission tracks in natural minerals. Geological Society of London, Special Publications, 324, 25–36.10.1144/SP324.2Search in Google Scholar
Gleadow, A., Harrison, M., Kohn, B., Lugo-Zazueta, R., and Phillips, D. (2015) The Fish Canyon Tuff: A new look at an old low-temperature thermochronology standard. Earth and Planetary Science Letters, 424, 95–108.10.1016/j.epsl.2015.05.003Search in Google Scholar
Green, P.F., and Durrani, S.A. (1977) Annealing studies of tracks in crystals. Nuclear Track Detection, 1, 33–39.10.1016/B978-1-4832-8338-8.50034-0Search in Google Scholar
Green, P.F., Duddy, I.R., Gleadow, A.J.W., Tingate, P.R., and Laslett, G.M. (1986) Thermal annealing of fission tracks in apatite. 1. A qualitative description. Chemical Geology: Isotope Geoscience Section, 59, 237–253.10.1016/0168-9622(86)90074-6Search in Google Scholar
Green, P.F., Duddy, I.R., Laslett, G.M., Hegarty, K.A., Gleadow, A.J.W., and Lovering, J.F. (1989) Thermal annealing of fission tracks in apatite 4. Quantitative modelling techniques and extension to geological timescales. Chemical Geology: Isotope Geoscience Section, 79, 155–182.10.1016/0168-9622(89)90018-3Search in Google Scholar
Jonckheere, R. (2003) On methodical problems in estimating geological temperature and time from measurements of fission tracks in apatite. In Radiation Measurements, 36, 43–55.10.1016/S1350-4487(03)00096-9Search in Google Scholar
Jonckheere, R., Enkelmann, E., Min, M., Trautmann, C., and Ratschbacher, L. (2007) Confined fission tracks in ion-irradiated and step-etched prismatic sections of Durango apatite. Chemical Geology, 242, 202–217.10.1016/j.chemgeo.2007.03.015Search in Google Scholar
Jonckheere, R., Tamer, M.T., Wauschkuhn, B., Wauschkuhn, F., and Ratschbacher, L. (2017) Single-track length measurements of step-etched fission tracks in Durango apatite: “vorsprung durch Technik.” American Mineralogist, 102, 987–996.Search in Google Scholar
Jonckheere, R., Wauschkuhn, B., and Ratschbacher, L. (2019) On growth and form of etched fission tracks in apatite: A kinetic approach. American Mineralogist, 104, 569–579.10.2138/am-2019-6762Search in Google Scholar
Ketcham, R.A. (2005) Forward and inverse modeling of low-temperature thermo-chronometry data. Reviews in Mineralogy and Geochemistry, 58, 275–314.10.2138/rmg.2005.58.11Search in Google Scholar
Ketcham, R.A. (2015) Technical Note: Calculation of stoichiometry from EMP data for apatite and other phases with mixing on monovalent sites. American Mineralogist, 100, 1620–1623.10.2138/am-2015-5171Search in Google Scholar
Ketcham, R.A. (2019) Fission track annealing: from geologic observations to thermal modeling. In P.G. Fitzgerald and M. Malusa, Eds., Fission Track Thermochronology and its Application to Geology, p. 49–75. Springer.10.1007/978-3-319-89421-8_3Search in Google Scholar
Ketcham, R.A., Donelick, R.A., and Carlson, W.D. (1999) Variability of apatite fission-track annealing kinetics: III. Extrapolation to geological timescales. American Mineralogist, 84, 1235–1255.10.2138/am-1999-0903Search in Google Scholar
Ketcham, R.A., Carter, A., Donelick, R.A., Barbarand, J., and Hurford, A.J. (2007) Improved measurement of fission-track annealing in apatite using c-axis projection. American Mineralogist, 92, 799–810.10.2138/am.2007.2280Search in Google Scholar
Ketcham, R.A., Donelick, R.A., Balestrieri, M.L., and Zattin, M. (2009) Reproducibility of apatite fission-track length data and thermal history reconstruction. Earth and Planetary Science Letters, 284, 504–515.10.1016/j.epsl.2009.05.015Search in Google Scholar
Ketcham, R.A., Carter, A., and Hurford, A.J. (2015) Inter-laboratory comparison of fission track confined length and etch figure measurements in apatite. American Mineralogist, 100, 1452–1468.10.2138/am-2015-5167Search in Google Scholar
Ketcham, R.A., van der Beek, P., Barbarand, J., Bernet, M., and Gautheron, C. (2018) Reproducibility of thermal history reconstruction from apatite fission-track and (U-Th)/He data. Geochemistry, Geophysics, Geosystems, 19, 2411–2436.10.1029/2018GC007555Search in Google Scholar
Laslett, G.M., and Galbraith, R.F. (1996) Statistical properties of semi-tracks in fission track analysis. Radiation Measurements, 26, 565–576.10.1016/1350-4487(96)00027-3Search in Google Scholar
Laslett, G.M., Gleadow, A.J.W., and Duddy, I.R. (1984) The relationship between fission track length and track density in apatite. Nuclear Tracks and Radiation Measurements, 9, 29–38.10.1016/0735-245X(84)90019-XSearch in Google Scholar
Li, Q., Gleadow, A., Seiler, C., Kohn, B., Vermeesch, P., Carter, A., and Hurford, A. (2018) Observations on three-dimensional measurement of confined fission track lengths in apatite using digital imagery. American Mineralogist, 103, 430–440.10.2138/am-2018-6156Search in Google Scholar
Meitner, L., and Frisch, O.R. (1939) Disintegration of uranium by neutrons: A new type of nuclear reaction. Nature, 143, 239–240.10.1038/143239a0Search in Google Scholar
Miller, D. S., Eby, N., McCorkell, R., Rosenberg, P.E., and Suzuki, M. (1990) Results of interlaboratory comparison of fission track ages for the 1988 fission track workshop. International Journal of Radiation Applications and Instrumentation, Part, 17, 237–245.10.1016/1359-0189(90)90041-USearch in Google Scholar
Murakami, M., Yamada, R., and Tagami, T. (2006) Short-term annealing characteristics of spontaneous fission tracks in zircon: A qualitative description. Chemical Geology, 277, 214–222.10.1016/j.chemgeo.2005.10.002Search in Google Scholar
Naeser, C.W., Zimmerman, R.A., and Cebula, G.T. (1981) Fission-track dating of apatite and zircon: an interlaboratory comparison. Nuclear Tracks, 5, 65–72.10.3133/ofr78108Search in Google Scholar
Paul, T.A., and Fitzgerald, P.G. (1992) Transmission electron microscopic investigation of fission tracks in fluorapatite. American Mineralogist, 77, 336–344.Search in Google Scholar
Sobel, E., and Seward, D. (2010) Influence of etching conditions on apatite fission-track etch pit diameter. Chemical Geology, 271, 59–69.10.1016/j.chemgeo.2009.12.012Search in Google Scholar
Spiegel, C., Kohn, B., Raza, A., Rainer, T., and Gleadow, A. (2007) The effect of long-term low-temperature exposure on apatite fission track stability: A natural annealing experiment in the deep ocean. Geochimica et Cosmochimica Acta, 71, 4512–4537.10.1016/j.gca.2007.06.060Search in Google Scholar
Tamer, M. T. (2012) The lengths of fossil and induced fission tracks in Durango apatite. Technische Universitaet Bergakademie Freiberg. Masters thesis, 37 p.Search in Google Scholar
Tamer, M.T., and Ketcham, R.A. (2018) Is low-temperature fission-track annealing in apatite a thermally controlled process? 16th International Conference On Thermochronology, Germany/Quedlinburg. Conference proceedings.10.1029/2019GC008877Search in Google Scholar
Wagner, G.A. (1981) Fission-track ages and their geological interpretation. Nuclear Tracks, 5, 15–25.10.1016/0191-278X(81)90022-6Search in Google Scholar
Wagner, G.A., Gleadow, A.J.W., and Fitzgerald, P.G. (1989) The significance of the partial annealing zone in apatite fission-track analysis: Projected track length measurements and uplift chronology of the transantarctic mountains. Chemical Geology: Isotope Geoscience Section, 79, 295–305.10.1016/0168-9622(89)90035-3Search in Google Scholar
Watt, S., and Durrani, S.A. (1985) Thermal stability of fission tracks in apatite and sphene: Using confined-track-length measurements. Nuclear Tracks and Radiation Measurements, 10, 349–357.10.1016/0735-245X(85)90124-3Search in Google Scholar
Watt, S., Green, P.F., and Durrani, S.A. (1984) Studies of annealing anisotropy of fission tracks in mineral apatite using Track-in-Track (tint) length measurements. Nuclear Tracks and Radiation Measurements, 8, 371–375.10.1016/0735-245X(84)90123-6Search in Google Scholar
Ziegler, J.F., Biersach, P.J., and Ziegler, M.D. (2008) SRIM The Stopping and Range of Ions in Matter, vol. 05, 390 pp. SRIM Co. Chester, Maryland.Search in Google Scholar
© 2019 Walter de Gruyter GmbH, Berlin/Boston
