Isotope dilution analysis of Ca and Zr in apatite and zircon (U-Th)/He chronometry

Guenthner, William R.; Reiners, Peter W.; Chowdhury, Uttam Kumar

doi:10.1002/2016gc006311

Cited by 39 publications

(35 citation statements)

References 14 publications

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“…Larger uncertainty on a subset of the dates is due to low measured U and Th. We conservatively applied a 20% uncertainty to all eU values, which is consistent with a recent study that compared stoichiometric and morphologic methods for apatite and zircon volume estimates and found average eU percent differences of 15% and 25%, respectively (Guenthner et al, ). This is also consistent with the estimates of Baughman et al ().…”

Section: Methodssupporting

confidence: 78%

Rutile (U‐Th)/He Thermochronology: Temperature Sensitivity and Radiation Damage Effects

Robinson

Flowers

Metcalf

2019

Geochem Geophys Geosyst

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Rutile (TiO2) is a common U‐Th‐bearing accessory mineral in metamorphic and, to a lesser extent, igneous rocks. Its development as a (U‐Th)/He thermochronometer would diversify the lithologies dateable with the (U‐Th)/He technique. We report (U‐Th)/He dates for rutile with crystallization ages that vary from Cretaceous to Proterozoic from eight samples with independent constraints on their thermal history to empirically calibrate the temperature sensitivity of the rutile (U‐Th)/He (RHe) system. The results document an analytical challenge for the Proterozoic rutile, where degassing at laser powers typical for zircon volatilized the parent isotopes while lower laser powers failed to consistently and completely extract all 4He from the crystals. In contrast, the six Phanerozoic samples were easily degassed without U‐Th loss. RHe dates for five of these samples are fairly reproducible (6–22% dispersion) or yield positive RHe date‐eU correlations. RHe dates are older than or overlap with apatite (U‐Th)/He dates available for four of these samples and are younger than zircon (U‐Th)/He dates available for two of these samples. This implies that the He closure temperature (Tc) for these Phanerozoic rutile is between apatite (~70 °C) and lower damage zircon (~200 °C). We also conducted two 4He diffusion experiments. These data are consistent with anisotropic He diffusion and yield Tc estimates of ~155–159 °C for diffusion parallel to the c axis (at a 10 °C/Ma cooling rate). These diffusion experiment results, the degassing patterns for Phanerozoic versus Proterozoic rutile, and the positive RHe date‐eU correlations in two samples imply that radiation damage increases rutile He retentivity.

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Section: Methodssupporting

confidence: 78%

Rutile (U‐Th)/He Thermochronology: Temperature Sensitivity and Radiation Damage Effects

Robinson

Flowers

Metcalf

2019

Geochem Geophys Geosyst

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“…(U–Th)/He dating has a historical perspective, with Ernest Rutherford reporting the first radioisotopic date using a U–He system in 1904. In the last three decades, a resurgence of interest in dating minerals with 4 He ingrowth has been facilitated by an improved understanding of the behavior of He in minerals (Farley, ; Flowers et al, ; Gautheron et al, ; Guenthner et al, ; Lippolt et al, ; Reiners et al, ; Shuster et al, ; Shuster & Farley, ; Stockli & Farley, ; Wolf et al, ; Zeitler et al, ) and development of robust analytical techniques (Farley, ; Farley et al, ; Guenthner et al, ). This method can be applied to address geological problems operative over 10 5 to 10 9 years, as well as high‐temperature, short‐duration thermal pulses.…”

Section: Foundationmentioning

confidence: 99%

Innovations in (U–Th)/He, Fission Track, and Trapped Charge Thermochronometry with Applications to Earthquakes, Weathering, Surface‐Mantle Connections, and the Growth and Decay of Mountains

2019

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A transformative advance in Earth science is the development of low‐temperature thermochronometry to date Earth surface processes or quantify the thermal evolution of rocks through time. Grand challenges and new directions in low‐temperature thermochronometry involve pushing the boundaries of these techniques to decipher thermal histories operative over seconds to hundreds of millions of years, in recent or deep geologic time and from the perspective of atoms to mountain belts. Here we highlight innovation in bedrock and detrital fission track, (U–Th)/He, and trapped charge thermochronometry, as well as thermal history modeling that enable fresh perspectives on Earth science problems. These developments connect low‐temperature thermochronometry tools with new users across Earth science disciplines to enable transdisciplinary research. Method advances include radiation damage and crystal chemistry influences on fission track and (U–Th)/He systematics, atomistic calculations of He diffusion, measurement protocols and numerical modeling routines in trapped charge systematics, development of 4He/3He and new (U–Th)/He thermochronometers, and multimethod approaches. New applications leverage method developments and include quantifying landscape evolution at variable temporal scales, changes to Earth's surface in deep geologic time and connections to mantle processes, the spectrum of fault processes from paleoearthquakes to slow slip and fluid flow, and paleoclimate and past critical zone evolution. These research avenues have societal implications for modern climate change, groundwater flow paths, mineral resource and petroleum systems science, and earthquake hazards.

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“…Therefore, mass fractions of U, Th and Sm were calculated from the measured isotopic content and estimated fragment mass. Detailed protocols are described by Guenthner et al (2016).…”

Section: Conventional (U-th)/he Geochronologymentioning

confidence: 99%

MK‐1 Apatite: A New Potential Reference Material for (U‐Th)/He Dating

Shi

Danišík

et al. 2019

Geostandard Geoanalytic Res

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The (U‐Th)/He dating technique has been widely used for several decades to constrain the timing of low temperature geological processes. Recent research has shown that the commonly used reference material (the Durango apatite) often yields dispersed fragment dates that are beyond analytical uncertainties. Here, we report a new apatite (U‐Th)/He dating reference material, MK‐1, which was collected from the Mogok metamorphic belt in Burma. Electron probe microanalysis and backscattered electron images of two randomly selected fragments indicate that this apatite is chemically and structurally homogeneous. We performed single‐grain (U‐Th)/He dating on thirty randomly selected fragments of this material. (U‐Th)/He dating results from multiple laboratories show that fragments of the MK‐1 apatite megacryst yielded reproducible results, with a mean date of 18.0 ± 0.2 Ma. The Th/U ratio of this apatite is homogeneous. Nine randomly selected fragments registered a narrow range of effective uranium (eU) mass fractions (326–354 μg g−1), with a mean value of 336.6 ± 10.3 μg g−1. Twenty‐four in situ (U‐Th)/He dates yielded a mean value of 18.0 ± 0.2 Ma (MSWD = 0.41), indistinguishable from the results obtained by the conventional method. All the results suggest that this apatite has the potential to become a new reference material for (U‐Th)/He geochronology.

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Isotope dilution analysis of Ca and Zr in apatite and zircon (U-Th)/He chronometry

Cited by 39 publications

References 14 publications

Rutile (U‐Th)/He Thermochronology: Temperature Sensitivity and Radiation Damage Effects

Rutile (U‐Th)/He Thermochronology: Temperature Sensitivity and Radiation Damage Effects

Innovations in (U–Th)/He, Fission Track, and Trapped Charge Thermochronometry with Applications to Earthquakes, Weathering, Surface‐Mantle Connections, and the Growth and Decay of Mountains

MK‐1 Apatite: A New Potential Reference Material for (U‐Th)/He Dating

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