Metamictisation of natural zircon: accumulation versus thermal annealing of radioactivity-induced damage

Nasdala, Lutz; Wenzel, Marita; Vavra, G.; Irmer, G.; Wenzel, Thomas J.; Kober, B

doi:10.1007/s004100000235

Cited by 369 publications

(363 citation statements)

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“…Mechanisms proposed as being responsible for these effects include metamictisation due to radiation damage (e.g. Nasdala et al 2001;Ewing et al 2003), annealing of radiation damage (e.g. Nasdala et al 2002), fluid alteration (e.g.…”

Section: Introductionmentioning

confidence: 99%

Zircon ages in granulite facies rocks: decoupling from geochemistry above 850 °C?

Kunz

Regis

Engi

2018

Contrib Mineral Petrol

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Granulite facies rocks frequently show a large spread in their zircon ages, the interpretation of which raises questions: Has the isotopic system been disturbed? By what process(es) and conditions did the alteration occur? Can the dates be regarded as real ages, reflecting several growth episodes? Furthermore, under some circumstances of (ultra-)high-temperature metamorphism, decoupling of zircon U-Pb dates from their trace element geochemistry has been reported. Understanding these processes is crucial to help interpret such dates in the context of the P-T history. Our study presents evidence for decoupling in zircon from the highest grade metapelites (> 850 °C) taken along a continuous high-temperature metamorphic field gradient in the Ivrea Zone (NW Italy). These rocks represent a well-characterised segment of Permian lower continental crust with a protracted high-temperature history. Cathodoluminescence images reveal that zircons in the mid-amphibolite facies preserve mainly detrital cores with narrow overgrowths. In the upper amphibolite and granulite facies, preserved detrital cores decrease and metamorphic zircon increases in quantity. Across all samples we document a sequence of four rim generations based on textures. U-Pb dates, Th/U ratios and Ti-in-zircon concentrations show an essentially continuous evolution with increasing metamorphic grade, except in the samples from the granulite facies, which display significant scatter in age and chemistry. We associate the observed decoupling of zircon systematics in high-grade non-metamict zircon with disturbance processes related to differences in behaviour of non-formula elements (i.e. Pb, Th, U, Ti) at high-temperature conditions, notably differences in compatibility within the crystal structure.

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Section: Introductionmentioning

confidence: 99%

Zircon ages in granulite facies rocks: decoupling from geochemistry above 850 °C?

Kunz

Regis

Engi

2018

Contrib Mineral Petrol

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“…With increasing metamictization, all main Raman bands decrease in intensity, become increasingly broader, and shift towards lower wavenumbers. These changes are due to decreasing short-range order in the radiation-damaged zircon (Nasdala et al, 2004). In the case of natural zircons, decreased short-range order is mainly caused by radiation damage.…”

Section: High-uranium Effectmentioning

confidence: 96%

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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“…The magnitude of this anomaly depends on the redox condition of the melt/fluid from which the zircon has crystallized 38 .…”

Section: +mentioning

confidence: 99%

Paleoarchean Zircons from Quartzite of South Bundelkhand Supracrustal Complex:Origin and Implications for Crustal Evolution in Bundelkhand Craton, Central India

Слабунов¹,

Singh²,

Joshi³

et al. 2017

Current Science

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The present study reports trace elemental data from 39 Paleoarchean (3.43 and 3.25 Ga) zircons separated from quartzite near Girar, which forms a part of the South Bundelkhand Supracrustal Complex in Central India. The zircons are prismatic, have well-developed oscillatory zoning and their Th/U ratio ranging from 0.27 to 8.62 is comparable to that of typical magmatic zircons. Crystallization temperature of 620-776C using titanium-in-zircon thermometer, positive slope of zircon REE patterns, positive Ce anomalies along with mineral inclusions like quartz, muscovite, magnetite and monazite suggest a granitic source for these quartzites. Sm-Nd isotopic data (T DM age = 3.29 Ga) along with zircon trace elemental data indicate the presence of granitic continental crust in southern Bundelkhand Craton at least during the Paleoarchean (3.4 Ga).

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Metamictisation of natural zircon: accumulation versus thermal annealing of radioactivity-induced damage

Cited by 369 publications

References 0 publications

Zircon ages in granulite facies rocks: decoupling from geochemistry above 850 °C?

Zircon ages in granulite facies rocks: decoupling from geochemistry above 850 °C?

Extreme isotopologue disequilibrium in molecular SIMS species during SHRIMP geochronology

Paleoarchean Zircons from Quartzite of South Bundelkhand Supracrustal Complex:Origin and Implications for Crustal Evolution in Bundelkhand Craton, Central India

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