High-uranium matrix effect in zircon and its implications for SHRIMP U–Pb age determinations

White, L.B.; Ireland, Trevor

doi:10.1016/j.chemgeo.2012.02.025

Cited by 206 publications

(88 citation statements)

References 32 publications

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“…8), are positively correlated with U. This is consistent with the findings of White and Ireland (2012) that SHRIMP analysis of higher-U zircon yielded erroneous ages related to instrumental fractionation or matrix effects. Alternatively, the positive correlation could be explained by the addition of Pb to the zircon (e.g., Williams et al, 1984) or removal of U (less likely, given the high U concentrations); either of these could result in the same relationship.…”

Section: Rift Magmatism and Comparison With The Border Riftsupporting

confidence: 80%

U-Pb ages of igneous xenoliths in a salt diapir, La Popa basin: Implications for salt age in onshore Mexico salt basins

Lawton

Amato

2017

Lithosphere

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Ar cooling ages from a nearby diapir, which are younger than Upper Jurassic strata overlying the salt, combine to suggest that these samples were intruded into salt and exhumed during diapirism. A porphyritic mafic rock with a U-Pb zircon age of 150 Ma (Tithonian) has a crystallization age coeval with marine strata overlying the salt. It is interpreted as a shallow intrusion into salt emplaced after the onset of salt diapirism. Magmatism thus took place from 158 to 150 Ma.

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Section: Rift Magmatism and Comparison With The Border Riftsupporting

confidence: 80%

U-Pb ages of igneous xenoliths in a salt diapir, La Popa basin: Implications for salt age in onshore Mexico salt basins

Lawton

Amato

2017

Lithosphere

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“…Exceptionally high concentrations in U or analysis of metamict domains in zircon can be a cause of reverse discordance, owing to matrix-related ion yield effects (Williams and Hergt, 2000;White and Ireland, 2012;Kusiak et al, 2013). Neither elevated U concentrations nor significant metamict alteration in zircon domains have been observed.…”

Section: U-pb (Zircon) Geochronologymentioning

confidence: 99%

Time constraints on magmatism, mineralisation and metamorphism at the Falun base metal sulphide deposit, Sweden, using U–Pb geochronology on zircon and monazite

Kampmann

Stephens

Ripa

et al. 2016

Precambrian Research

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a b s t r a c t U-Th-Pb (zircon and monazite) ion probe data have provided constraints on the timing of emplacement and metamorphism of magmatic rocks close to the Palaeoproterozoic, Falun base metal sulphide deposit in the Bergslagen lithotectonic unit, Fennoscandian Shield, Sweden, and, thereby the timing of mineralisation. Hydrothermal alteration and mineralisation at Falun are constrained to a short interval of several million years between a 207 Pb/ 206 Pb weighted average age of 1894 ± 3 Ma for a rhyolitic sub-volcanic rock in the felsic volcanic to sub-volcanic host rock suite, and a 207 Pb/ 206 Pb weighted average age of 1891 ± 3 Ma for a post-sulphide, porphyritic dacite dyke. Magmatism also included the emplacement of granite plutons with igneous crystallization ages of 1894 ± 3, 1894 ± 2 Ma and 1893 ± 3 Ma. The felsic sub-volcanic to volcanic activity and the emplacement of dacite dykes and granite plutons overlap in age within their respective analytical uncertainties, indicating hydrothermal alteration and sulphide mineralisation inside a narrow time span of intense magmatic activity, and burial of the supracrustal rocks. Two distinct patchy and homogeneous metamorphic monazite types in a felsic volcanic rock around and hydrothermally altered rocks at the Falun deposit yield 207 Pb/ 206 Pb weighted average ages of 1831 ± 8 Ma and 1822 ± 5 Ma, respectively. These ages fall well within the temporal range of a younger 1.84-1.81 Ga (M 2 ) metamorphic episode during the 2.0-1.8 Ga Svecokarelian orogeny, with the older episode (M 1 ) inside the Bergslagen lithotectonic unit at around 1.86 Ga. This shows the major influence of the M 2 event in the north-western part of this unit, leading to a complete resetting of the U-Th-Pb isotope system in monazite.

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“…7). White and Ireland (2012) have shown that Jurassic high-U zircons which show an apparent U-concentration effect are metamict, according to the spectral featured described in Nasdala et al (1995).…”

Section: High-uranium Effectmentioning

confidence: 99%

“…The ∼ 36 Ma Raumid and ∼ 180 Ma Red Hill (Williams and Hergt, 2000;White and Ireland, 2012) zircons show a 274 excess up to about 0.1. However, the 0.8 Ma Bishop Tuff zircons, which do not seem to exhibit this high-uranium effect (Chamberlain et al, 2014;Ickert et al, 2015), have only one analytical spot with a 274 above 0.025, and none above (Fig.…”

Section: High-uranium Effectmentioning

confidence: 99%

“…Firstly, the covariation is not exact, and after calibration there remains a residual error that is rarely better than 0.5 %. Secondly, it requires corrections for bulk composition for zircons with more than 2000 ppm U (Williams and Hergt, 2000;White and Ireland, 2012), or for minerals that exhibit complex solid solution, such as monazite (Gregory et al, 2007;Fletcher et al, 2010). Thirdly, some simple oxides, such as baddeleyite and rutile, exhibit orientation-related deviations from the calibration (Wingate and Compston, 2000;Schmitt et al, 2010;Taylor et al, 2012).…”

Section: W Magee Jr Et Al: Isotopologue Disequilibrium In Simsmentioning

confidence: 99%

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Extreme isotopologue disequilibrium in molecular SIMS species during SHRIMP geochronology

Magee

Danišík

Mernagh

2017

Geosci. Instrum. Method. Data Syst.

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Abstract. The current limitation in the accuracy and precision of inter-element analysis in secondary ion mass spectrometry (SIMS) is the ability to find measurable quantities that allow relative differences in ionization and transmission efficiency of secondary ions to be normalized. In uraniumthorium-lead geochronology, the ability to make these corrections, or "calibrate" the data, results in an accuracy limit of approximately 1 %. This study looks at the ionization of uranium and thorium oxide species, which are traditionally used in U-Pb calibration, to explore the conditions under which isotopologues, or molecular species whose composition differs only in the isotopic composition of one or more atoms in the molecule, remain in or deviate from equilibrium.Isotopologue deficits of up to 0.2 (200 ‰) below ideal mixing are observed in UO + 2 species during SIMS gechronological analyses using the SHRIMP IIe SIMS instrument. These are identified by bombarding natural U-bearing minerals with an 18 O − 2 primary beam. The large anomalies are associated with repeat analyses down a single SIMS sputtering crater (Compston et al., 1984), analysis of high-uranium, radiation-damaged zircon, and analysis of baddeleyite. Analysis of zircon under routine conditions yield UO + 2 isotopologue anomalies generally within a few percent of equilibrium. The conditions under which the isotopologue anomalies are observed are also conditions in which the UO x -based corrections, or calibration, for relative U vs. Pb ionization efficiencies fail. The existence of these isotopologue anomalies suggest that failure of the various UO x species to equilibrate with each other is the reason that none of them will successfully correct the U / Pb ratio. No simple isotopologuebased correction is apparent. However, isotopologue disequilibrium appears to be a more sensitive tool for detecting high-U calibration breakdowns than Raman spectroscopy, which showed sharper peaks for ∼ 37 Ma high-uranium zircons than for reference zircons OG1 and Temora. U-ThSm / He ages were determined for aliquots of reference zircons OG1 (755±71 Ma) and Temora (323±43 Ma), suggesting that the broader Raman lines for the Temora reference zircons may be due to something other than accumulated radiation damage.Isotopologue abundances for UO + and ThO + and their energy spectra are consistent with most or all molecular species being the product of atomic recombination when the primary beam impact energy is greater than 5.7 keV. This, in addition to the large UO + 2 instrumentally generated isotopologue disequilibria, suggests that any attempts to use SIMS to detect naturally occurring isotopologue deviations could be tricky.

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High-uranium matrix effect in zircon and its implications for SHRIMP U–Pb age determinations

Cited by 206 publications

References 32 publications

U-Pb ages of igneous xenoliths in a salt diapir, La Popa basin: Implications for salt age in onshore Mexico salt basins

U-Pb ages of igneous xenoliths in a salt diapir, La Popa basin: Implications for salt age in onshore Mexico salt basins

Time constraints on magmatism, mineralisation and metamorphism at the Falun base metal sulphide deposit, Sweden, using U–Pb geochronology on zircon and monazite

Extreme isotopologue disequilibrium in molecular SIMS species during SHRIMP geochronology

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