Fission-Track Annealing: From Geologic Observations to Thermal History Modeling

Ketcham, Richard A.

doi:10.1007/978-3-319-89421-8_3

Cited by 51 publications

(40 citation statements)

References 127 publications

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“…Comparing our new ZHe geochronology to the published low‐temperature thermochronology of the Phyllite‐Quartzite Unit across Crete allows us the timing correlation of displacement along the length of the detachment. Within eastern Crete, our data are significantly younger than the zircon fission track (ZFT) data of Brix et al (), which ranges from 414 ± 24 to 229 ± 14 Ma, with shortened track lengths, corresponding to partial annealing zone temperatures of 310–220 °C (Ketcham, ). Brix et al () also reported ZFT dates of 17 ± 2 to 18 ± 1 Ma within small fault bounded blocks in central Crete.…”

Section: Discussioncontrasting

confidence: 53%

Back to Normal: Direct Evidence of the Cretan Detachment as a North‐Directed Normal Fault During the Miocene

2019

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The Cretan Detachment represents a major tectonic contact between an Alpine high‐pressure Lower Nappe System in the footwall and an Alpine unmetamorphosed Upper Nappe System in the hanging wall. Interestingly, the kinematics and the tectonic nature of this contact is still highly controversial and has been interpreted either as a top‐to‐the S thrust or as a normal fault with top‐to‐the N and/or top‐to‐the S displacement sense. Whereas some models suggest exhumation of the high‐pressure rocks synchronous with out‐of‐sequence thrusting or Himalayan‐type extrusion tectonics, other models propose that Crete represents a metamorphic core complex that exhumed below the extensional Cretan Detachment. In this work, we show that the Cretan Detachment in eastern Crete is an up to 100‐m‐thick cataclastic low‐angle fault zone, which localized below the Tripolitza Unit (Upper Nappe System) within the upper part of the Upper Violet Slates (top of Lower Nappe System) cutting downsection to lower structural levels. The unequivocal kinematic indicators in this fault zone clearly suggest a top‐to‐the N displacement of the hanging wall. New low‐temperature geochronological data and numerical modeling suggest rapid cooling of the rocks in the footwall of the Cretan Detachment at circa 15 Ma. Top‐to‐the S ductile shear sense toward lower structural level in the Lower Nappe System support the idea that the Cretan Detachment facilitated the exhumation of the high‐pressure rocks in an extrusion tectonic setting. Therefore, in the early to middle Miocene, subduction‐related extrusion in Crete was simultaneously active with back‐arc extension‐related metamorphic core formation in the Cyclades.

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Section: Discussioncontrasting

confidence: 53%

Back to Normal: Direct Evidence of the Cretan Detachment as a North‐Directed Normal Fault During the Miocene

2019

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“…Thermal history inversion using low-temperature thermochronological data is a widely used technique with a range of geologic applications, from rifting and basin evolution to mountain building and landscape development (e.g., Gallagher et al, 1998;Lisker et al, 2009;Malusa & Fitzgerald, 2018;Reiners & Brandon, 2006). The reproducibility of these methods is critically important to their soundness and the degree of confidence that can be placed in their results.…”

Section: Introductionmentioning

confidence: 99%

Reproducibility of Thermal History Reconstruction From Apatite Fission‐Track and (U‐Th)/He Data

Ketcham

Beek

Barbarand

et al. 2018

Geochem Geophys Geosyst

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We report a new interlaboratory exercise to evaluate the reproducibility of apatite fission‐track (AFT) and (U‐Th)/He (AHe) data and thermal history analysis. Twelve laboratory groups participated, analyzing apatite separates from two previously studied localities. Ten groups returned AFT data from 13 analysts, five groups returned AHe data, one contributed apatite U/Pb data, and nine contributed thermal history models. Submitted AFT age data were generally consistent with the original studies and each other to within uncertainties, although there were departures, particularly among results obtained using laser ablation inductively coupled plasma mass spectrometry for uranium determination. AFT‐confined track‐length data showed more variation, which correlated between samples, suggesting that they may reflect analyst‐specific factors. Accounting for anisotropy using c axis projection reduced the variation and correlation. AHe ages showed more dispersion than observed in the previous studies, with one sample showing many ages consistent with prior work but also many significantly older ages, and the other roughly matching prior work but showing symmetrical scatter suggesting a 1SE uncertainty of 17–21%. Thermal history models generally agreed in their major features but showed considerable variation in detail, due to differences in data and data entry, model setup, and modeling software approach. Addressing pitfalls in data entry and model setup improved congruence, as would greater emphasis on AFT length and etch figure calibration. Because of scatter, AHe data had to be entered selectively into the models to achieve reasonable results. Although cautionary in several respects, study results point to promising avenues for improving the reproducibility of thermal history modeling.

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“…Typically, model parameters are fitted by minimizing the misfit between model equation predictions and the data, and different model equations are evaluated and compared based on their degree of misfit and residuals (e.g., Laslett et al, ; Laslett & Galbraith, ), as well at their predictions against geological benchmarks (Ketcham et al, ). Because the various proposed empirical annealing equations overlap greatly over the limited time and temperature range of laboratory experiments (e.g., Ketcham, ; Figure 3.9), extending this range provides a new opportunity to distinguish models by providing more space for them to diverge. Previous annealing studies covered temperature ranges of ~100 to ~450 °C and durations from ~30 min up to a couple of months, while this study extends annealing temperatures down to ~23 °C and broadens the time range to span from 39 s to ~32 years (Figure ).…”

Section: Discussionmentioning

confidence: 99%

“…The Donelick et al () result is consistent with spontaneous confined track lengths being shorter than induced tracks in Fish Canyon Tuff (28 ± 2 Ma) apatite and Durango apatite (31 ± 3 Ma), which have been assumed to have not experienced significant heating above ambient earth‐surface temperatures since emplacement (Gleadow et al, ; McDowell et al, ). A reanalysis of the Donelick et al () data for Tioga apatite, combined with higher‐temperature experiments by Donelick (), indicates that this low‐temperature annealing is well described by the empirical equations used to characterize fission‐track annealing (e.g., Donelick et al, ; Ketcham et al, ; Laslett et al, ), suggesting that it may be controlled by the same process (Ketcham, , Figure 3.12). However, these data sets were generated with an etching protocol that is no longer used, and the high‐temperature experiments may have suffered from temperature calibration issues (Carlson et al, ), making this result suggestive but not definitive.…”

Section: Introductionmentioning

confidence: 94%

Is Low‐Temperature Fission‐Track Annealing in Apatite a Thermally Controlled Process?

Tamer

Ketcham

2020

Geochem Geophys Geosyst

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We report a new series of experiments to explore the phenomenon of low‐temperature annealing of fission tracks in apatite that feature a number of improvements over previous work. Grain mounts were preirradiated using 252Cf to increase confined track detection and allow briefer thermal neutron irradiation. We coirradiated and etched four apatite varieties (Durango, Fish Canyon, Renfrew, and Tioga) over five time steps equally spaced from 3.66 to 15 ln(s). A length standard was coetched with all experiments to ensure that subtle differences are within detection limits. Finally, we used a standard etching protocol, allowing the data to be comodeled with extensive high‐temperature data sets and recent analyses of induced tracks that underwent ambient‐temperature annealing over year‐to‐decade time scales. Ambient‐temperature annealing occurs at two different rates, with faster annealing at early stages that decreases to a slower rate that converges with empirical fanning linear or curvilinear models. The nature of this decrease varies among the apatite species examined, but no patterns could be determined. The fitted models make geological time‐scale predictions consistent with those based on high‐temperature data only and also make predictions consistent with reasonable inferred low‐temperature histories for all four apatite varieties. The empirical fanning curvilinear equation encompasses low‐temperature annealing at month‐to‐decade time scales, but low‐temperature annealing at shorter time scales may occur by a distinct mechanism. We consider but rule out annealing by radiation from short‐lived activated isotopes. We also reconsider the notion of the initial track length, and the appropriate length for normalizing confined track length measurements.

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Fission-Track Annealing: From Geologic Observations to Thermal History Modeling

Cited by 51 publications

References 127 publications

Back to Normal: Direct Evidence of the Cretan Detachment as a North‐Directed Normal Fault During the Miocene

Back to Normal: Direct Evidence of the Cretan Detachment as a North‐Directed Normal Fault During the Miocene

Reproducibility of Thermal History Reconstruction From Apatite Fission‐Track and (U‐Th)/He Data

Is Low‐Temperature Fission‐Track Annealing in Apatite a Thermally Controlled Process?

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