Metamictization and chemical durability of detrital zircon

Balan, Etienne; Neuville, Daniel R.; Trocellier, P.; Fritsch, Emmanuel; Müller, Jean‐Pierre; Calas, Georges

doi:10.2138/am-2001-8-909

Cited by 129 publications

(70 citation statements)

References 35 publications

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“…By 200 days after synthesis, the dose imparted to the material is approximately 1x10 18 alpha-events/g. This value is similar to the values given by Ewing and coworkers (Ewing and Headley 1983;Balan et al 2001) for the dose of amorphization of pyrochlore and zircon, respectively.…”

Section: Discussionsupporting

confidence: 91%

“…A number of studies Begg et al (2000) of radiation damage in natural titanate minerals have shown that the host phase becomes metamict after >1.0x10 18 alpha-events/g or ~1 dpa (displacements per atom). Balan et al (2001) argued that metamictization becomes an important factor in the aqueous durability of natural zircon crystals when the amorphized regions become interconnected. They proposed that a dose of ~3.5x10…”

Section: Discussionmentioning

confidence: 99%

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The Status of Radiation Damage Experiments

Strachan¹,

Scheele²,

Icenhower³

et al. 2001

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SummaryThis is a status report on the progress of the radiation damage experiments that are being performed at the Pacific Northwest National Laboratory in support of the Plutonium Immobilization Program (PIP) to dispose plutonium that is surplus to the defense needs of the US. This report covers the progress of radiation damage from the decay of 238 Pu to the titanate phases that comprise the PIP ceramic. With the exception of brannerite, all the phases are represented in the specimens we are testing and characterizing. The phases appear to damage faster than anticipated from the information in the literature. Pyrochlore appears to become metamict 2 to 3 times faster. Zirconolite is more resistant, but this depends on what impurities are present.Radiation damage results in swelling of the specimens. After 650 days, the trend in the data suggest that swelling will continue as the damage process appears to be incomplete (it has not yet "saturated" or reached a steady-state condition). The decrease in density from swelling is between 8 % and 15%, based on measurements of the pyrochlore baseline and a zirconolite-rich ceramic. The linear expansion of the specimen dimensions is between 2% and 5%.The dissolution rate appears to be between 500 -1000 times greater for a 238 Pu-bearing pyrochlore baseline sample than for the corresponding 239 Pu specimen. Although we believe that this increase in rate is due to radiation damage, we cannot be absolutely certain because we did not manage to obtain SPFT data on these specimens before damage started to accumulate. It is possible that the increased rate is due to some effect related to the higher dose rate and radiation field near the 238 Pu specimens that we don't understand.

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Section: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 99%

The Status of Radiation Damage Experiments

Strachan¹,

Scheele²,

Icenhower³

et al. 2001

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“…These silcretes have higher levels of Zr ( Figure 7A), Al, K, Na, Rb, Pb, Nb and Y than are typical of the other duricrust samples, probably due to incorporation of zircon and feldspar (and/or weathered clay derived from the feldspar) from the underlying granitoid-gneiss. The ratio of the physical contributions of the granitoid-gneiss and Kalahari Group sands to the lower silcrete is approximately 1:3, calculated from the median Zr concentrations of the bedrock (384 ppm), lower silcrete (144 ppm) and remaining duricrusts (41 ppm, representative of the Kalahari Group sands), assuming that Zr is chemically immobile (Webb and Golding, 1998;Balan, et al, 2001).…”

Section: Geochemistry: Kang Pan and Tswaane Quarrymentioning

confidence: 99%

Petrology, geochemistry and environmental significance of silcrete‐calcrete intergrade duricrusts at Kang Pan and Tswaane, central Kalahari, Botswana

Nash

McLaren

Webb

2004

Earth Surf Processes Landf

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Calcrete–silcrete intergrade duricrusts are an important component of the Kalahari Group sediments of central southern Africa and yet have neither been analysed systematically nor in any detail. In this study, the petrological and geochemical characteristics of suites of calcrete, silcrete and intergrade duricrusts from two fresh, relatively deep exposures at Kang Pan and Tswaane (adjacent to the Okwa Valley) in the central Kalahari, Botswana, are described. The duricrust profile at Kang Pan consists of a highly indurated crystalline non-pedogenic calcrete which has been extensively silicified by chalcedony, and, rarely, cryptocrystalline silica or microquartz. Silicification is most extensive in lower parts of the profile, where replacement is related to groundwater fluctuations, and in upper sections due to periodic flooding by ephemeral surface water.\ud The exposure at Tswaane consists of a sequence of pale green glauconitic non-pedogenic silcrete and cal-silcrete overlain by non-pedogenic calcrete, all of which have formed within sediments situated upon granitoid-gneiss bedrock. The siliceous duricrusts are dominated by cryptocrystalline silica cements and appear to have developed through the replacement of a preexisting non-pedogenic calcrete. These siliceous duricrusts have also been calcified at a later date during the formation of\ud the overlying calcrete to produce a complex range of silica–carbonate cements. At both sites, the style and type of silicification present appears to be determined by the duration of wetting and the permeability of the precursor calcrete. Geochemical evidence indicates a lack of chemical weathering profile development within the granitoid–gneiss bedrock and considerable differences between the chemical signature of the bedrock and combined duricrusts from Kang and Tswaane. This suggests that bedrock made a minimal contribution in terms of silica and carbonate species to duricrust formation, and that the majority of cementing agents were non-local. It would therefore appear likely that the geomorphological context of each site had a major influence upon the development of calcrete, silcrete and intergrade duricrust cements

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“…This zircon has an ID -TIMS weighted mean 206 Pb/ 238 U age of 2.508 ± 0.002 Ma. On the one hand, the 230 Th disequilibrium effect cannot be corrected, because the because they are young, they are unlikely to have suffered any radiation damage [32] . Consequently, all 206 Pb/ 238 U ages are assumed to be meaningful.…”

Section: La -Mc -Icp -Ms Results Applied To Young Reference Zirconsmentioning

confidence: 99%