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TitleApatite fission track thermal history analysis of the Beaufort-Mackenzie Basin, Arctic Canada: a natural laboratory for testing multi-kinetic thermal annealing models
 
AuthorIssler, D RORCID logo; Grist, A M
SourceThermo 2014, 14th International Conference on Thermochronology, abstract program; 2014 p. 125-126
LinksOnline - En ligne
Image
Year2014
Alt SeriesEarth Sciences Sector, Contribution Series 20140016
MeetingThermo 2014 - 14th International Conference on Thermochronology; Chamonix; FR; September 8-12, 2014
Documentbook
Lang.English
Mediapaper; on-line; digital
File formatpdf
ProvinceYukon; Northwest Territories
NTS107; 117
AreaBeaufort-Mackenzie Basin
Lat/Long WENS-144.0000 -128.0000 72.0000 68.0000
Subjectsgeochronology; thermal analyses; thermal history; apatite; fission-track dates; models; modelling
Illustrationslocation maps
ProgramGEM: Geo-mapping for Energy and Minerals Mackenzie Delta and Corridor
AbstractThe Arctic Beaufort-Mackenzie basin (BMB) is a natural laboratory for testing composition-based apatite fission track (AFT) annealing models because it comprises compositionally homogeneous Upper Cretaceous-Cenozoic deltaic successions with highly variable heating/cooling histories and long residence times in the AFT partial annealing zone. Sixty AFT (mainly core) samples from 25 wells are available from Paleogene post-rift (Aklak, Taglu, Richards and Kugmallit sequences), Upper Jurassic-Lower Cretaceous syn-rift (Husky, Martin Creek and Kamik formations), and Devonian pre-rift (Imperial Formation) successions (Figure 1). All major tectonic elements are sampled, including the western Tertiary fold belt, Tertiary growth faults of the Tarsiut-Amauligak and Taglu fault zones, the Kugmallit Trough (formed by Jurassic-Early Cretaceous rifting), and intact continental crust of the Anderson Basin to the southeast. Multi-parameter well data (e.g., temperature1, 2, 3, stratigraphy, thermal maturity4 and porosity) were compiled for integrated thermal history analysis as part of a major government-industry funded study of BMB petroleum systems.
Samples collected during the initial phase of the study (generally at low thermal maturity; < 0.5 %Ro) yielded mainly single grain ages that passed the chi-squared test, giving an initial impression of compositionally uniform AFT age populations. Subsequent sampling from successions with higher thermal maturity (> 0.5 %Ro) yielded many samples with single grain ages that failed the chi-squared test, indicating mixed AFT age populations within samples. Further analysis of single grain ages using the binomial peak-fitting program (Binomfit) of Mark Brandon (Yale University) suggests that most of the samples have two statistically significant age populations. This interpretation is supported by elemental data and microscopic observations that show significant variability in elemental abundances and etch figure sizes (Dpar) among apatite grains. The rmr0 parameter6 (based on elemental data) is more successful at defining separate statistical AFT populations with distinct annealing kinetics than widely used kinetic parameters based on chlorine content or Dpar. Elemental data indicate that most samples have two statistical kinetic populations with different annealing properties that behave as separate thermochronometers: a fluorine-rich apatite (lower track retentivity) and an iron-rich apatite (higher track retentivity).
Low uranium concentrations of apatite grains, rapid exhumation of sediment source areas, and variable degrees of post-depositional annealing present challenges to defining statistical kinetic populations. However, insight into multi-kinetic annealing is gained by examining the spatial variation in AFT data within a regional thermal maturity framework4, leading to successful multikinetic thermal models that satisfy available geological constraints. Apatite composition is similar for all Paleogene samples with approximately equal abundances of fluorine-rich and iron-rich apatite. The apparent uniform AFT age of low maturity samples can be attributed to rapid cooling of apatite source areas and this eliminates variation in detrital provenance age as a factor in modeling. The different kinetic populations within a sample can be modeled using the same thermal history, indicating that compositionally-related differential annealing is the main factor causing grain age dispersion at higher thermal maturity. The fluorine-rich apatite is more sensitive to the post-depositional thermal history whereas the iron-rich apatite retains information on the predepositional rapid cooling history of detrital apatite source areas. AFT data from other areas of western and northern Canada suggest that compositional variation in detrital apatite is common and needs to be considered when undertaking thermochronology studies.
Summary(Plain Language Summary, not published)
Apatite fission track (AFT) thermochronology is a powerful method for quantifying the thermal history of rock samples. It is useful to oil exploration because it provides time-temperature information in the temperature range for petroleum generation. The arctic Beaufort-Mackenzie Basin has a unique set of AFT samples with compositionally-variable apatite minerals from Paleozoic, Mesozoic and Cenozoic rocks that permit enhanced resolution of the thermal history of this petroleum-rich sedimentary basin. This presentation outlines interpretation and modelling methods for treating statistical populations of apatite grains with different chemical compositions as separate thermochronometers that constrain different parts of the thermal history. AFT data quantify the rate, magnitude and timing of cooling related to deep erosion of the basin margin, and the high heating rate of rapidly deposited Cenozoic deltaic sediments.
GEOSCAN ID293881

 
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