Computational Tools for Low-Temperature Thermochronometer Interpretation

Ehlers, Todd A.; Chaudhri, Tehmasp; Kumar, Santosh; Fuller, Chris W.; Willett, Sean D.; Ketcham, Richard A.; Brandon, M. T.; Belton, David; Kohn, Barry P.; Gleadow, A. J. W.; Dunai, Tibor J.; Fu, Frank Q.

doi:10.2138/rmg.2005.58.22

Cited by 175 publications

(161 citation statements)

References 54 publications

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“…The (U‐Th)/He method is used to track the time since a mineral cooled below closure temperatures of ~55–90 °C for apatite and ~160–200 °C for zircon (e.g., Ehlers et al, 2005). The effective closure temperature of any sample depends on the cooling rate, grain size, mineralogy, and radiation damage (e.g., Farley, 2000; Flowers et al, 2009; Reiners et al, 2004, 2005).…”

Section: Bedrock Thermochronometrymentioning

confidence: 99%

Slow Long‐Term Exhumation of the West Central Andean Plate Boundary, Chile

2018

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We present a regional analysis of new low‐temperature thermochronometer ages from the Central Andean fore arc to provide insights into the exhumation history of the western Andean margin. To derive exhumation rates over 10 million‐year timescales, 38 new apatite and zircon (U‐Th)/He ages were analyzed along six ~500‐km long near‐equal‐elevation, coast parallel, transects in the Coastal Cordillera (CC) and higher‐elevation Precordillera (PC) of the northern Chilean Andes between latitudes 18.5°S and 22.5°S. These transects were augmented with age‐elevation profiles where possible. Results are synthesized with previously published thermochronometric data, corroborating a previously observed trenchward increase in cooling ages in Peru and northern Chile. One‐dimensional thermal‐kinematic modeling of all available multichronometer equal‐elevation samples reveals mean exhumation rates of <0.2 km/Myr since ~50 Ma in the PC and ~100 Ma in the CC. Regression of pseudovertical age‐elevation transects in the CC yields comparable rates of ~0.05 to ~0.12 km/Myr between ~40 and 80 Ma. Differences between the long‐term mean 1‐D rates and shorter‐term age‐elevation‐derived rates indicate low variability in the exhumation history. Modeling results suggest similar background exhumation rates in the CC and PC; younger ages in the PC are largely a function of increased heat flow and consequently an elevated geothermal gradient near the arc. Slow exhumation rates are suggestive of semiarid conditions across the region since at least the Eocene and deformation and development of the Andean fore arc around this time.

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Section: Bedrock Thermochronometrymentioning

confidence: 99%

Slow Long‐Term Exhumation of the West Central Andean Plate Boundary, Chile

2018

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“…The thermal-kinematic model functions as: (1) a kinematic model that uses fault geometries and high-resolution point tracking inputs from the Move software to calculate rock transport (advection) velocities; (2) a transient thermal model that calculates the thermal field using fault motion, erosion above the 10 topographic surface, rock thermophysical properties, and thermal boundary conditions; and (3) a set of age prediction algorithms (Ehlers et al, 2005) that calculate a suite of thermochronometer ages for material at the topographic surface for each deformation step using the thermal histories of particles as they are exhumed and cooled from depth to the model surface (e.g. Coutand et al, 2014;McQuarrie and Ehlers, 2015).…”

Section: Thermal and Cooling Age Prediction Modelmentioning

confidence: 99%

Testing the effects of topography, geometry and kinematics on modeled thermochronometer cooling ages in the eastern Bhutan Himalaya

Gilmore¹,

McQuarrie²,

Eizenhöfer³

et al. 2017

Preprint

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Abstract. The temporal and kinematic evolution of fold-thrust belts is a critical component for evaluating the viability of proposed plate tectonic, geodynamic and even climatic processes in regions of convergence. Thermochronometer data have the potential to provide temporal constraints, but interpretations of these data are sensitive to both exhumational and deformational processes. In this study, reconstructions of a balanced geologic cross section in the Himalayan fold-thrust belt 10 of eastern Bhutan are used in a flexural and thermal-kinematic model to understand the sensitivity of predicted cooling ages to changes in fault kinematics, geometry and topography. We sequentially deform the cross section with ~10-km deformation steps and apply flexural loading and erosional unloading at each step to develop a high-resolution evolution of deformation, erosion, and burial over time.Comparison of model-predicted cooling ages to published thermochronometer data reveals that cooling ages are most 15 sensitive to (1) location and magnitude of fault ramps, (2) variable shortening rates between 68-6.4 mm/yr, and (3) timing and magnitude of out-of-sequence faulting. The predicted ages are less sensitive to (4) radiogenic heat production, and (5) estimates of topographic evolution. We propose a revised cross section geometry that separates one large ramp previously proposed for the modern decollement into two smaller ramps. The revised cross section results in an improved fit to observed ages, particularly young AFT ages (2-6 Ma) located north of the Main Central Thrust. 20

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“…cooling rate, using an updated version of the FTINDEX program (Ehlers et al 2005). This value is somewhat artificially bounded by the condition of linear cooling to an assumed earth-surface temperature of 20°C as implemented by the program.…”

Section: Discussionmentioning

confidence: 99%

Annealing behavior of alpha recoil tracks in phlogopite

et al. 2009

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In this study we present and interpret a new experimental data set documenting thermal annealing of alpha recoil tracks (ARTs) in phlogopite. Through improvements in experimental technique, difficulties in obtaining useable data from material with an uneven distribution of U and Th were overcome. The resulting annealing pattern was well organized on an Arrhenius plot, allowing construction of a simple, 3-parameter annealing model of parallel contours of constant annealing with a linear progression. Our data and model indicate that phlogopite ARTs anneal at very low temperatures on geological time scales. At the million-year time scale, full annealing requires a temperature of only 33°C, and we infer closure temperatures from 26-37°C for cooling rates of 10-100°C/m.y. Phlogopite ART analysis is thus likely to be primarily useful in relatively young (b1 Ma) terrains featuring either recent volcanism or recent, fast exhumation. In such situations, however, it may provide unique information on the timing of the final stages of unroofing. Comparison of our results with previous studies on ART and fission-track annealing in phlogopite and biotite indicates that these two types of radiation damage anneal at disparate time and temperature conditions in biotite-series micas.

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Computational Tools for Low-Temperature Thermochronometer Interpretation

Cited by 175 publications

References 54 publications

Slow Long‐Term Exhumation of the West Central Andean Plate Boundary, Chile

Slow Long‐Term Exhumation of the West Central Andean Plate Boundary, Chile

Testing the effects of topography, geometry and kinematics on modeled thermochronometer cooling ages in the eastern Bhutan Himalaya

Annealing behavior of alpha recoil tracks in phlogopite

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