The microstructure of zircon and its influence on the age determination from Pb/U isotopic ratios measured by ion microprobe

McLaren, A. C.; Gerald, John Fitz; Williams, Ian S.

doi:10.1016/0016-7037(94)90521-5

Cited by 192 publications

(77 citation statements)

References 23 publications

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“…The strongest is at 2 Å −1 , there are two at about 3.5 and 3.9 Å −1 and the weakest is at around 6 Å −1 . This profile matches very well with the diffraction pattern previously reported and obtained by electron diffraction (Murakami et al 1991, McLaren et al 1994, Capitani et al 2000. In the latter measurements the first ring was at 2.0 Å −1 , which agrees with our first peak.…”

Section: Resultssupporting

confidence: 91%

Amorphization in zircon: evidence for direct impact damage

Rı́os¹,

Salje²,

Zhang³

et al. 2000

J. Phys.: Condens. Matter

125

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Abstract. X-ray diffraction has been used to characterize the amorphous phase present in a series of radiation-damaged natural zircons with radiation doses ranging from 0.06 to 16 × 10 18 α-decay events g −1 . The fraction of amorphous material present in each of the samples studied has been determined, and its dependence on the radiation dose has been calibrated. Direct determination of the amorphous fraction confirms that amorphization in natural zircon occurs as a consequence of the direct impact within cascades caused by α-recoil nuclei. These results are not consistent with the commonly accepted double-overlap model of damage accumulation.The volume swelling of amorphous regions changes as a function of dose. Thus, the density of amorphous regions depends on the degree of damage up to a certain point (i.e. 8 × 10 18 α-decay events g −1 ), unlike in previous models for which a constant value independent of the radiation dose was assumed.

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Section: Resultssupporting

confidence: 91%

Amorphization in zircon: evidence for direct impact damage

Rı́os¹,

Salje²,

Zhang³

et al. 2000

J. Phys.: Condens. Matter

125

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“…4b). The data point 14.1 shows reverse discordance, which may be attributed from the reliability of the U-Pb calibration or the secondary emission yield of the labile Pb (e.g., McLaren et al, 1994;Wiedenbeck, 1995).…”

Section: Resultsmentioning

confidence: 99%

SHRIMP U–Pb zircon ages of granitoids adjacent to Chitradurga shear zone, Dharwar craton, South India and its tectonic implications

Nasheeth

Okudaira

Horie

et al. 2015

Journal of Mineralogical and Petrological Sciences

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We report newly obtained U-Pb SHRIMP ages of zircons from the granitoids in the vicinity of Chitradurga shear zone of Dharwar craton, South India. The analyses yielded two different ages, an older age of ca. 3300 Ma and younger ages of~2600-2650 Ma, those suggest two major igneous activities in the study area. The former activity contemporaneous with the formation of Mesoarchean (~3.3 Ga) basement rocks (i.e., Peninsular Gneiss) and the latter reflects the Neoarchean (~2.6 Ga) regional plutonic activity in the Western Dharwar craton. Field and petrographic observations suggest that the intensity of deformation is high at the boundary between amphibolites and granitoids. Our new age dates imply that the formation of Chitradurga shear zone postdated the magmatic activity in the study area and the deformation structures possibly related to the development of Chitradurga shear zone. The area on either sides of the boundary between Eastern and Western Dharwar cratons experienced a Neoproterozoic event between 700-600 Ma indicated by prominent SHRIMP lower intercepts.

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“…Zircon does not self-anneal at low temperatures so is often found in nature to be metamict; the higher temperature annealing of natural radiation damage has been extensively studied by optical, X-ray and TEM techniques. For low degrees of damage it seems to anneal back to the single crystal state; at intermediate levels of damage, new zircon crystallites nucleate in the amorphous regions and the crystals anneal to a mosaic state; while with high levels of damage, the samples anneal to ZrO 2 and SiO 2 , which persist as separate phases to at least 1200°C (McLaren, 1994;Murakami, 1991, Woodhead, 1991. In fact, there is now some doubt as to whether zircon is a truly stable ambient pressure phase.…”

Section: Crystal Structure Model Of Monazitementioning

confidence: 99%