Effects of weathering on the UPb ages of zircon from the Morton Gneiss, Minnesota

Stern, T. W.; Goldich, Samuel S.; Newell, M.F.

doi:10.1016/0012-821x(66)90027-6

Cited by 58 publications

(19 citation statements)

References 8 publications

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“…The limited recovery had apparently a profound effect on the stability of U and Th, which were extensively removed from the reaction zones, compared with the comparatively high stability of these cations in the 450 ∞C-experiments of Geisler et al (2001b). The enhanced susceptibility of metamict zircon to lose Pb, U, and Th at low temperatures in the presence of a fluid, where structural recovery is minimal, was a significant result from that study and can explain loss of Pb, and possible U, from weathered zircon crystals (e.g., Stern et al 1966).…”

Section: Introductionmentioning

confidence: 97%

Experimental hydrothermal alteration of partially metamict zircon

Geisler

Pidgeon

Kurtz

et al. 2003

American Mineralogist

274

140

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We present the results of a series of hydrothermal experiments on grains from two partially metamict zircon samples from Sri Lanka in the temperature range 350 to 650 ∞C and with different solutions (2 M AlCl 3 , 2 M CaCl 2 , pure H 2 O, and a multi-cation solution). Under these conditions, sharply bounded reaction fronts penetrated into the zircon grains and developed complex lobate and rim structures that resemble structures found in natural zircon systems. The reaction zones are characterized by a marked increase in the cathodoluminescence intensity, a decrease of the back-scattered electron emission, and an increased degree of structural order, as revealed by micro-Raman and infrared spectroscopy. Sensitive high-resolution ion microprobe and electron microprobe measurements revealed that the altered areas gained solvent cations (e.g., Ca 2+ , Ba 2+ , Mg 2+ , Al 3+ ) from the solution and lost variable amounts of Zr, Si, Hf, the REE, U, Th as well as radiogenic Pb. A comparison between "dry" and "hydrothermal" annealing trends shows that the kinetics of structural recovery, including recrystallization of the amorphous phase in metamict zircon, is strongly enhanced under hydrothermal conditions. This finding suggests that water "catalyzes" structural recovery processes in metamict zircon. We found that the structure of the reacted areas does not resemble that of crystalline zircon, i.e., is still characterized by a temperature-dependent degree of disorder, which would not be expected if the reaction is controlled by a coupled dissolution and re-precipitation process. Instead, the alteration process can be described best by a diffusion-reaction-recrystallization model. In this model, it is postulated that the diffusion of water into the metamict structure is the driving force for moving recrystallization fronts. We found that the rate and the extent of solid-state recrystallization of the amorphous phase is an important factor in determining the mobility of trace elements. This interpretation is indicated by the observation that trace elements, including U and Th, were preferentially lost during the reaction with a fluid at low temperatures, where recrystallization of the amorphous material was slow or not activated at all. The observed chemical alteration patterns are believed to reflect a competition between the kinetics of long-range diffusion and ion exchange and the kinetics of the short-range diffusion necessary for the recrystallization process.

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Section: Introductionmentioning

confidence: 97%

Experimental hydrothermal alteration of partially metamict zircon

Geisler

Pidgeon

Kurtz

et al. 2003

American Mineralogist

274

140

View full text Add to dashboard Cite

show abstract

“…Catanzaro and Kulp (1964) argued that discordance in zircon from the Beartooth, Little Belt and Santa Catalina Mountains was due to Pb loss caused, in some cases by metamorphism, in others by groundwater leaching. By analyzing zircon from weathered parts of the Archean gneiss dated by Catanzaro (1963), Stern et al (1966) demonstrated that zircon could lose 50-85% of its radiogenic Pb even at ambient temperature. Such open system characteristics were evidently related to the metamict state of the zircon.…”

Section: Isotopic Dating Of Zircon -1955 To 1973mentioning

confidence: 98%

Historical Development of Zircon Geochronology

Davis

Williams

Krogh

2003

Reviews in Mineralogy and Geochemistry

165

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“…hydrothermal activity) is a likely candidate for inducing Pb loss in the inherited zircon crystals (producing the discordia), as well as causing a minor disturbance to zircon fraction 1 of the c. 411 Ma magmatic zircon population (Silver & Deutsch 1963;Stern et al 1966;Hansen & Friderichsen 1989;Mezger & Krogstad 1997;Geisler et al 2003). Such hydrothermal activity and dissolution-precipitation reactions are likely candidates for inducing Pb loss (Geisler et al 2007, and references within), with resultant textures easily observable using electron microscopy.…”

mentioning

confidence: 97%