Unraveling the exhumation history of high-pressure ophiolites using magnetite (U-Th-Sm)/He thermochronometry

Schwartz, Stéphane; Gautheron, Cécile; Ketcham, Richard A.; Brunet, Fabrice; Corre, Marianna; Agranier, Arnaud; Pinna-Jamme, Rosella; Haurine, Fréderic; Monvoin, Gael; Riel, Nicolas

doi:10.1016/j.epsl.2020.116359

Cited by 16 publications

(33 citation statements)

References 59 publications

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“…Another possible process is thermal annealing acting over geological times and during the degassing experiments. In the former case we presume that the temperature needed to get a significant annealing is high (above 200 • C) and this is compatible with the age for the sample Rocher Blanc magnetite from the Schistes Lustrés (Western Alps) [21] (see below). During the degassing experiments, the annealing is usually negligible, although the temperature is high, due to the short dwelling time of the steps.…”

Section: Theoretical Damage Quantificationsupporting

confidence: 60%

“…Due to the petrological importance of magnetite, during the last fifteen years special attention has been devoted to the development and application of the magnetite (U-Th)/He thermo-geochronology method (e.g., [17][18][19][20][21]). Knowledge of helium diffusivity in magnetite is a prerequisite for the geological interpretation of magnetite (U-Th)/He data.…”

Section: Introductionmentioning

confidence: 99%

“…The first and only He diffusion dataset was obtained on a magnetite crystal from the Bala Cretaceous kimberlite [17] and revealed He retentive behavior, with a calculated closure temperature of ~250 • C assuming 10 • C/Myr cooling and a sphere equivalent radius of 250 µm. The discovery of such a high closure temperature has paved the way for research into the use of the magnetite (U-Th)/He method to date the exhumation of mafic and ultramafic rocks [19,21], which are characterized by a scarcity of minerals that can be analyzed with (U-Th)/He thermochronometers. This new tool has been used to constrain the timing and duration of fossil hydrothermal mineralization and on serpentinite exhumation in a subduction-collision zone [20,22], respectively.…”

Section: Introductionmentioning

confidence: 99%

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Role of Defects and Radiation Damage on He Diffusion in Magnetite: Implication for (U-Th)/He Thermochronology

et al. 2022

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The discovery of He retentivity in magnetite has opened up the use of the magnetite (U-Th)/He method as a thermochronometer to date the exhumation of mafic and ultramafic rocks, and also as a chronometer to date magnetite crystallization during serpentinization. However, published He diffusion data reveal more complex behavior than expected. To resolve this issue and generalize the understanding of He retention in magnetite, we conducted a multiscale theoretical study. We investigated the impact of natural point-defects (i.e., vacancies unrelated to radiation damage) and defects associated with radiation damage (i.e., vacancies and recoil damage that form amorphous zones) on He diffusion in magnetite. The theoretical results show that He diffusion is purely isotropic, and that defect-free magnetite is more He diffusive than indicated by experimental data on natural specimen. Interestingly, the obtained theoretical trapping energy of vacancies and recoil damage are very similar to those obtained from experimental diffusion data. These results suggest that He diffusion in magnetite is strongly controlled by the presence of vacancies and radiation damage, even at very low damage dose. We propose that, when using magnetite (U-Th)/He thermochronometry, the impact of vacancies and radiation damage on He retention behavior should be integrated.

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Section: Theoretical Damage Quantificationsupporting

confidence: 60%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Role of Defects and Radiation Damage on He Diffusion in Magnetite: Implication for (U-Th)/He Thermochronology

et al. 2022

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“…After peak burial between 62 and 55 Ma for LPU and LPM (Agard et al, 2002) and around 50-45 Ma for the Monviso LPL (Rubatto and Hermann, 2003;Rubatto and Angiboust, 2015;Garber et al, 2020), the four units of the Queyras-Monviso transect were exhumed from late Eocene to Miocene times (Schwartz et al, 2007(Schwartz et al, , 2020Angiboust and Glodny, 2020)…”

Section: The Queyras-monviso Traversementioning

confidence: 99%

Along-dip variations of subduction fluids: The 30–80 km depth traverse of the Schistes Lustrés complex (Queyras-Monviso, W. Alps)

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Agard

et al. 2021

Lithos

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“…Another possible source of 3 He in minerals is 3 H produced as a result of ternary fission of U (Vorobiev et al, 1969;Halpern, 1971). This component is generally negligible for U concentrations < 10 ppm (Farley et al, 2006), but can be an important component when inclusions with high effective uranium concentrations ([eU] Shuster et al, 2006), such as apatite and zircon, are present. The kinetic energy of fissiogenic 3 H of 8.1 ± 0.2 MeV (Vorobiev et al, 1969) leads to an average ejection distance of 121 µm within magnetite and 264 µm in the soil.…”

Section: Production Of 3 He In Magnetitementioning

confidence: 99%

Exposure dating of detrital magnetite using <sup>3</sup>He enabled by microCT and calibration of the cosmogenic <sup>3</sup>He production rate in magnetite

et al. 2021

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Abstract. We test whether X-ray micro-computed tomography (microCT) imaging can be used as a tool for screening magnetite grains to improve the accuracy and precision of cosmogenic 3He exposure dating. We extracted detrital magnetite from a soil developed on a fanglomerate at Whitewater, California, which was offset by the Banning strand of the San Andreas Fault. This study shows that microCT screening can distinguish between inclusion-free magnetite and magnetite with fluid or common solid inclusions. Such inclusions can produce bulk 3He concentrations that are significantly in excess of the expected spallation production. We present Li concentrations, major and trace element analyses, and estimated magnetite (U–Th) / He cooling ages of samples in order to model the contribution from fissiogenic, nucleogenic, and cosmogenic thermal neutron production of 3He. We show that mineral inclusions in magnetite can produce 3He concentrations of up to 4 times that of the spallation component, leading to erroneous exposure ages. Therefore, grains with inclusions must be avoided in order to facilitate accurate and precise magnetite 3He exposure dating. Around 30 % of all grains were found to be without inclusions, as detectable by microCT, with the largest proportion of suitable grains in the grain size range of 400–800 µm. While grains with inclusions have 3He concentrations far in excess of the values expected from existing 10Be and 26Al data in quartz at the Whitewater site, magnetite grains without inclusions have concentrations close to the predicted depth profile. We measured 3He concentrations in aliquots without inclusions and corrected them for Li-produced components. By comparing these data to the known exposure age of 53.5 ± 2.2 ka, we calibrate a production rate for magnetite 3He at sea level and high latitude (SLHL) of 116 ± 13 at g−1 a−1. We suggest that this microCT screening approach can be used to improve the quality of cosmogenic 3He measurements of magnetite and other opaque mineral phases for exposure age and detrital studies.

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Unraveling the exhumation history of high-pressure ophiolites using magnetite (U-Th-Sm)/He thermochronometry

Cited by 16 publications

References 59 publications

Role of Defects and Radiation Damage on He Diffusion in Magnetite: Implication for (U-Th)/He Thermochronology

Role of Defects and Radiation Damage on He Diffusion in Magnetite: Implication for (U-Th)/He Thermochronology

Along-dip variations of subduction fluids: The 30–80 km depth traverse of the Schistes Lustrés complex (Queyras-Monviso, W. Alps)

Exposure dating of detrital magnetite using <sup>3</sup>He enabled by microCT and calibration of the cosmogenic <sup>3</sup>He production rate in magnetite

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Unraveling the exhumation history of high-pressure ophiolites using magnetite (U-Th-Sm)/He thermochronometry

Cited by 16 publications

References 59 publications

Role of Defects and Radiation Damage on He Diffusion in Magnetite: Implication for (U-Th)/He Thermochronology

Role of Defects and Radiation Damage on He Diffusion in Magnetite: Implication for (U-Th)/He Thermochronology

Along-dip variations of subduction fluids: The 30–80 km depth traverse of the Schistes Lustrés complex (Queyras-Monviso, W. Alps)

Exposure dating of detrital magnetite using &lt;sup&gt;3&lt;/sup&gt;He enabled by microCT and calibration of the cosmogenic &lt;sup&gt;3&lt;/sup&gt;He production rate in magnetite

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Exposure dating of detrital magnetite using <sup>3</sup>He enabled by microCT and calibration of the cosmogenic <sup>3</sup>He production rate in magnetite