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TitleCharacterisation, interpretation and modelling of multi-kinetic apatite fission track data using elemental data
AuthorIssler, D R
SourceThermo 2018: 16th International Conference on Thermochronology, conference abstracts; 2018 p. 95
LinksOnline - En ligne (complete volume - volume complet, pdf, 9.72 MB)
Year2018
Alt SeriesNatural Resources Canada, Contribution Series 20180133
MeetingThermo 2018 - 16th International Conference on Thermochronology; Quedlinburg; DE; 16-21 September, 2018
Documentbook
Lang.English
Mediapaper; on-line; digital
File formatpdf
Subjectsgeochronology; fission-track dates; apatite; modelling; thermal analyses; thermal history; temperature; provenance; methodology; apatite fission track (AFT) dating; apatite fission track annealing; kinetic analyses; Phanerozoic; Cenozoic; Tertiary; Mesozoic; Paleozoic
ProgramMackenzie Corridor, Shield-to-Selwyn geo-transect, Mackenzie-Selwyn sub-activity, GEM2: Geo-mapping for Energy and Minerals
Released2018 09 01
AbstractIt is very common for sedimentary rock samples to have compositionally-variable detrital apatite with overdispersed apatite fission track (AFT) ages. Proper characterization of AFT annealing kinetics is essential for determining whether differential thermal annealing and/or variable provenance are the cause for the age dispersion. Although the widely used single kinetic parameters, Cl content and D(par), may work for simple apatite compositions, they are generally inadequate for resolving multi-kinetic annealing behavior in more typical detrital samples with heterogeneous apatite compositions. The r(mr0) parameter, determined using elemental data, is able to resolve multiple statistical AFT kinetic populations for a large suite (> 150 samples) of Phanerozoic age (Cambrian through Eocene) samples from northern Canada that contain apatite with highly variable cation (Fe, Mn, Mg, Na, Sr, La, Y, Ce) and anion (F, Cl, OH) concentrations. In general, these same populations cannot be distinguished using Cl or D(par) due to substantial or complete overlap of population age and length data in kinetic parameter space. Analysis of 340 duplicate sets of apatite elemental data from 50 of these Phanerozoic samples indicate that r(mr0) values, when expressed as "effective Cl" values, are reproducible to within ±0.03 apfu for the majority of the data (>80%). This uncertainty represents ~5-10% or less of the typical range of r(mr0) values for the apatite grains comprising these multi-kinetic samples, meaning much less overlap of age and length data across population boundaries. In contrast, >400 duplicate D(par) values for the same samples are reproducible within ±0.25 microns and ±0.50 microns, for 56% and 90% of the data, respectively, representing ±25% and ±50% of the typical range in D(par) values (~1 micron) for these samples. The large uncertainty in D(par), and the use of Cl only, means that application of these parameters can result in mixed, poorly-defined AFT kinetic populations that can bias model thermal history results.
Multi-kinetic modelling, constrained using elemental data, extends the time-temperature range and resolution of thermal histories in comparison to more conventional methods that use the single kinetic parameters, D(par) or Cl content. Although r(mr0) values are more precise than D(par) or Cl for defining kinetic populations, calculated values are less accurate beyond the dominant range of the annealing experimental calibration data (0.75 < r(mr0) < 0.84; Ketcham et al. 1999) and must be estimated through thermal modelling. AFTINV, an inverse multi-kinetic AFT thermal model, is used to obtain statistically-acceptable, geologically-constrained thermal solutions that fit observed AFT and vitrinite reflectance data. Multi-kinetic AFT samples from northern Canada can have two or three kinetic populations with geological annealing temperatures that can range from ~75°C to >200°C, consistent with temperatures inferred from annealing experiments. Such a broad temperature range can constrain thermal histories further back in time and allow for the resolution of multiple heating events.
Ketcham R.A., Donelick, R.A., and Carlson, W.D. 1999. Variability of apatite fission-track annealing kinetics: III. Extrapolation to geological time scales. American Mineralogist, 84: 1235-1255.
Summary(Plain Language Summary, not published)
Apatite fission track thermochronology is a powerful method for reconstructing the thermal history of rock samples at temperatures below 200°C. Sedimentary rock samples can be difficult to work with because apatite grains can be derived from multiple source areas with different thermal histories and apatite mineral compositions. A method is presented that uses detailed elemental data to sort mixed apatite grains into discrete populations for modelling, resulting in better resolved thermal histories.
GEOSCAN ID308425