Alpha thermochronology of carbonates

Copeland, Peter; Watson, E. Bruce; Urizar, S. Cristina; Patterson, Desmond B; Lapen, T. J.

doi:10.1016/j.gca.2007.07.004

Cited by 30 publications

(26 citation statements)

References 45 publications

(56 reference statements)

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“…This complexity is underscored by (U-Th)/He ages reported on a suite of known-age samples, several of which yield anomalously young ages. In contrast to the MDD behavior observed for some carbonates, Copeland et al (2007Copeland et al ( , 2015 find step-heating results for crinoid columnals that suggest He diffusion from a single domain is dominant in these samples. They suggest that the biotic origin of these samples produces a more uniform microstructure in the carbonate, which develops into large effective He diffusion domains upon heating.…”

Section: Introductioncontrasting

confidence: 61%

“…A synthetic calcite sample was obtained from Commercial Crystal Labs, the same material used by Copeland et al (2007) and Arvidson et al (2003). A dolomite specimen from Styria, Austria was obtained from the Smithsonian collection (USNM # R12596).…”

Section: Sample Preparationmentioning

confidence: 99%

“…More recent work by Copeland et al (2007) directly evaluates 4 He diffusion kinetics by soaking a variety of carbonates in pressurized 4 He gas and undertaking bulk step-heating experiments. The measured diffusion parameters predict closure temperatures from $54 to 90°C.…”

Section: Introductionmentioning

confidence: 99%

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Diffusion of helium in carbonates: Effects of mineral structure and composition

Cherniak

Amidon

Hobbs

et al. 2015

Geochimica et Cosmochimica Acta

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Diffusion of helium has been characterized in four carbonates: calcite, dolomite, magnesite, and aragonite. Cleaved or oriented and polished slabs of carbonate minerals were implanted with 100 keV or 3 MeV 3 He at doses of 5 Â 10 15 3 He/cm 2 and 1 Â 10 16 3 He/cm 2 , respectively, and annealed in 1-atm furnaces. 3 He distributions following diffusion experiments were measured with nuclear reaction analysis using the reaction 3 He(d,p) 4 He.Our results show that He diffusion in calcite is the fastest among the carbonates studied, with diffusivities progressively slower in magnesite, dolomite and aragonite. In the case of the isomorphic trigonal carbonates (calcite, dolomite, magnesite), these observations are broadly consistent with predictions based on lattice characteristics such as unit cell size and inter-atomic apertures, with diffusivities faster in more open carbonate structures. Dolomite is an exception to this trend, suggesting that its unique ordered R3 crystal structure may play a role in slowing helium diffusion. Diffusion is anisotropic in all of the trigonal carbonates, and is typically slowest for diffusion along the c direction, and faster for diffusion normal to c and in directions normal to cleavage surfaces. The patterns of diffusional anisotropy are predicted to first order by the size of limiting inter-atomic apertures along any given crystallographic direction, providing additional support to the concept of modeling crystal lattices as "molecular sieves" with regard to diffusion of helium.When the effects of anisotropy and diffusion domain size are considered, our results are in reasonable agreement with previous results from bulk degassing of natural samples. Modeling of helium diffusive loss shows that calcite and magnesite are unlikely to be retentive of helium on the Earth's surface for typical grain sizes and time/temperature conditions. Dolomite and aragonite may be retentive under cooler conditions, but because helium retention is strongly dependent on diffusion domain size, general predictions are difficult given the structural complexities of natural samples. Our axis-specific diffusion measurements across a range of carbonate compositions, evaluated through direct profiling, offer important constraints for modeling helium mobility in carbonates, and for understanding the influence of the complexities of carbonate structures on He outgassing patterns.

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Section: Introductioncontrasting

confidence: 61%

Section: Sample Preparationmentioning

confidence: 99%

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Diffusion of helium in carbonates: Effects of mineral structure and composition

Cherniak

Amidon

Hobbs

et al. 2015

Geochimica et Cosmochimica Acta

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“…Until the 1960s, these dates were regarded as geologically meaningless, but the eventual realization that daughter isotope loss is a predominantly diffusive process led Table 2 Diffusion data and bulk closure temperatures for important systems Diffusion parameters are for the mean of two gem-quality calcite rhombs assuming a ¼ 300 mm. Other carbonate samples studied by Copeland et al (2007) yielded diffusion parameters that differed slightly. f Based on kinetic parameters (frequency factor and activation energy for trapped energy release) from Murray and Wintle (1999) and Spooner and Questiaux (2001).…”

Section: Closure Temperature Theorymentioning

confidence: 99%

Thermochronology in Orogenic Systems

Hodges

2014

Treatise on Geochemistry

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“…Moreover, both fission-track and (U -Th)/He techniques have been used successfully to date the formation of supergene minerals such as some phosphates or vanadates, hematite, goethite, limonite, manganese oxides and carbonate minerals (e.g. Bender 1973; Lippolt et al 1995;Shuster et al 2005;Boni et al 2007;Copeland et al 2007). …”

Section: Absolute Datingmentioning

confidence: 99%

Apatite thermochronology in modern geology

Lisker

Ventura

Glasmacher

2009

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Fission-track and (U-Th-Sm)/He thermochronology on apatites are radiometric dating methods that refer to thermal histories of rocks within the temperature range of 408-125 8C. Their introduction into geological research contributed to the development of new concepts to interpreting time-temperature constraints and substantially improved the understanding of cooling processes within the uppermost crust. Present geological applications of apatite thermochronological methods include absolute dating of rocks and tectonic processes, investigation of denudation histories and long-term landscape evolution of various geological settings, and basin analysis.

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Alpha thermochronology of carbonates

Cited by 30 publications

References 45 publications

Diffusion of helium in carbonates: Effects of mineral structure and composition

Diffusion of helium in carbonates: Effects of mineral structure and composition

Thermochronology in Orogenic Systems

Apatite thermochronology in modern geology

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