U-Th zonation-dependent alpha-ejection in (U-Th)/He chronometry

Hourigan, J. K.; Reiners, Peter W.; Brandon, M. T.

doi:10.1016/j.gca.2005.01.024

Cited by 363 publications

(332 citation statements)

References 36 publications

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“…Ages were calculated following the methods of Meesters and Dunai (2005), and error was propagated through our analysis to accurately estimate uncertainty in resulting ages. All grains were measured using spatially calibrated photos taken across and down the c axis to calculate alpha ejection correction factors (Ft; e.g., Farley et al, 1996; Farley & Stockli, 2002; Hourigan et al, 2005; Ketcham et al, 2011) using the geometric models of Ketcham et al (2011). Throughout, we take a conservative error estimate of 5% on all Ft values derived from the maximum difference on select problematic grains between our Ft calculation and one modeled with a Matlab script, using a Monte Carlo alpha ejection simulation on 3‐D grain models built from our multiangle photos (Glotzbach et al, 2017).…”

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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“…Finally, the raw (U-Th)/He ages of zircon and apatite were form-corrected (Ft correction) following Farley et al (1996) and Hourigan et al (2005). Replicate analyses of Durango apatite over the period of this study yielded a mean (U-Th)/He age of 30.4 ± 1.7 Ma, which is in good agreement with the reference (U-Th)/He age of 31.12 ± 1.01 Ma (McDowell et al 2005).…”

Section: Aft Analytical Techniquesmentioning

confidence: 99%

Exhumation and uplift of the Sierras Pampeanas: preliminary implications from K–Ar fault gouge dating and low-T thermochronology in the Sierra de Comechingones (Argentina)

Löbens

Bense

Wemmer

et al. 2010

Int J Earth Sci (Geol Rundsch)

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The Sierras Pampeanas in central and northwestern Argentina constitute a distinct morphotectonic feature between 27°S and 33°S. The last stage of uplift and deformation in this area are interpreted to be closely related to the Andean flat-slab subduction of the Nazca plate beneath the South American plate. K-Ar fault gouge dating and low-temperature thermochronology along two transects within the Sierra de Comechingones reveal a minimum age for the onset of brittle deformation about 340 Ma, very low exhumation rates since Late Paleozoic time, as well as a total exhumation of about 2.3 km since the Late Cretaceous. New Ar-Ar ages (7.54-1.91 Ma) of volcanic rocks from the San Luis volcanic belt support the eastward propagation of the flat-slab magmatic front, confirming the onset of flat-slab related deformation in this region at 11.2 Ma. Although low-temperature thermochronology does not clearly constrain the signal of the Andean uplift, it is understood that the current structural relief related to the Comechingones range has been achieved after the exhumation of both fault walls (circa 80-70 Ma).

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“…Farley et al (1996) demonstrated that (U-Th)/He ages typically require correction for the effects of alpha-ejection from crystals. The age-zoned zircons typically show systematic core-to-rim zonation of U and Th that can cause inaccuracy in alpha-ejection-corrected (U-Th)/He ages (Farley et al, 1996;Reiners et al, 2004;Hourigan et al, 2005). In most cases of this study, the rims have higher U and lower Th than the cores.…”

Section: Figure 2 a Continuous Profile Ofmentioning

confidence: 81%

“…In most cases of this study, the rims have higher U and lower Th than the cores. Although in general this may cause a bias to younger ages in grains requiring alpha-ejection corrections, it is not likely to exceed ~10% to 15% (Hourigan et al, 2005) because most grains show core-to-rim concentration contrasts of less than a factor of ~2-3, and have opposing Th and U zonation patterns.…”

Section: Figure 2 a Continuous Profile Ofmentioning

confidence: 99%

Detrital zircon U-Pb-He double dating: A method of quantifying long- and short-term exhumation rates in collisional orogens

Wang

Campbell

Reiners

et al. 2014

Sci. China Earth Sci.

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A U-Pb-He double-dating method is applied to detrital zircons with core-rim structure from the Ganges River in order to determine average short-and long-term exhumation rates for the Himalayas. Long-term rates are calculated from the U/Pb ages of metamorphic rims of the grains that formed during the Himalayan orogeny and their crystallization temperatures, which are calculated from the Ti-in-zircon thermometer. Short-term rates are calculated from (U-Th)/He ages of the grains with appropriate closure temperatures. The results show that short-term rates for the Himalayas, which range from 0.70  0.09 to 2.67  0.40 km/Myr and average 1.75  0.59 (1) km/Myr, are higher and more varied than the long-term rates, which range from 0.84  0.16 to 1.85  0.35 km/Myr and average 1.26  0.25 (1) km/Myr. The differences between the long-term and short-term rates can be attributed to continuous exhumation of the host rocks in different mechanisms in continental collision orogen. The U/Pb ages of 44.0 ± 3.7 to 18.3 ± 0.5 Ma for the zircon rims indicate a protracted episode of ~25 Myr for regional metamorphism of the host rocks at deeper crust, whereas the (U-Th)/He ages of 42.2 ± 1.8 to 1.3 ± 0.2 Ma for the zircon grains represent a protracted period of ~40 Myr for exposure of the host rocks to shallower crustal level. In particular, the oldest (U-Th)/He ages of the zircon grains are close to the oldest U/Pb ages for the rims, indicating that some parcels of the rocks that contain zircons were rapidly exhumed from deep to shallow levels in the stage of collisional orogeny. On the other hand, some parcels of the rocks may have been carried upwards by thrust faults in the post-collisional stage. The parcels could be carried upwards by the thrust faults that steepen as they near the surface, or by transient movement faults so that areas of rapid exhumation became areas of slow exhumation and visa versa on a time scale of a few Myr in order to maintain the continuous exhumation. In this regard, the Ganges River must be preferentially sampling areas that are currently undergoing above average rates of uplift.zircon, U-Pb-He double-dating method, Himalayas, exhumation rate, collisional orogen Citation:Wang C Y, Campbell I H, Reiners P W, et al. 2014. Detrital zircon U-Pb-He double dating: A method of quantifying long-and short-term exhumation rates in collisional orogens.

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U-Th zonation-dependent alpha-ejection in (U-Th)/He chronometry

Cited by 363 publications

References 36 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

Exhumation and uplift of the Sierras Pampeanas: preliminary implications from K–Ar fault gouge dating and low-T thermochronology in the Sierra de Comechingones (Argentina)

Detrital zircon U-Pb-He double dating: A method of quantifying long- and short-term exhumation rates in collisional orogens

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