Trace-element segregation to dislocation loops in experimentally heated zircon
30
Citation
55
Reference
10
Related Paper
Citation Trend
Abstract:
Abstract To evaluate the mechanisms driving nanoscale trace element mobility in radiation-damaged zircon, we analyzed two well-characterized Archean zircons from the Kaapvaal Craton (southern Africa): one zircon remained untreated and the other was experimentally heated in the laboratory at 1450 °C for 24 h. Atom probe tomography (APT) of the untreated zircon reveals homogeneously distributed trace elements. In contrast, APT of the experimentally heated zircon shows that Y, Mg, Al, and Pb+Yb segregate to a set of two morphologically and crystallographically distinct cluster populations that range from 5 nm tori to 25 nm toroidal polyhedra, which are confirmed to be dislocation loops by transmission electron microscopy (TEM). The dislocation loops lie in {100} and {001} planes; the edges are aligned with <100>, <101>, and <001>. The largest loops (up to 25 nm diameter) are located in {100} and characterized by high concentrations of Mg and Al, which are aligned with <001>. The 207Pb/206Pb measured from Pb atoms located within all of the loops (0.264 ± 0.025; 1σ) is consistent with present-day segregation and confirms that the dislocation loops formed during our experimental treatment. These experimentally induced loops are similar to clusters observed in zircon affected by natural geologic processes. We interpret that differences in cluster distribution, density, and composition between experimentally heated and geologically affected zircon are a function of the radiation dose, the pressure-temperature-time history, and the original composition of the zircon. These findings provide a framework for interpreting the significance of clustered trace elements and their isotopic characteristics in zircon. Our findings also suggest that the processes driving cluster formation in zircon can be replicated under laboratory conditions over human timescales, which may have practical implications for the mineralogical entrapment of significant nuclear elements.Keywords:
Trace element
Io-ages obtained for glass-zircon pairs which were not consistent with expected ages were discussed on the basis of uranium and thorium distribution between zircon and glass. Uranium and thorium distribution between zircon and host rocks from dacites and granites were also discussed. Discordant Io-ages obtained for glass-zircon pairs with normal (Th/U)zircon/(Th/U)glass ratio are explained by early stage crysallization of the zircon in the magma. Discordant Io-ages with abnormal (Th/U)zircon/(Th/U)glass ratios suggest that the zircon was captured in the magma as xenoryst. The discrepancy between (Th/U)zircon/(Th/U)glass ratios (about 0.19) for dacites and (Th/U)zircon/(Th/U)whole rock ratios (about 0.12) for granites could be explained by crystallization of granitic zircon from liquid having chemical composition different from that of the whole rock of granite.
Metamictization
Cite
Citations (25)
Cite
Citations (4)
The intrusive rocks in El Sela area can be arranged from the oldest to the youngest into: two-mica granite and postgranitic dikes which include microgranite, dolerite and bostonite dikes. Zircon is the most abundant accessory mineral. Zircon morphology and geochemical features are good indicators for evolution of rocks. The aim of the work is to determine the morphology, internal structure and chemical composition of zircon to identify the difference of zircon in various intrusive rocks. Results show that morphologically, zircon in the two-mica granite is euhedral coarse- grained with zonation. It is represented by crystals up to 125 µm and corresponds to S10 and P2. Zircon in post-granitic dikes exhibit irregular forms. Geochemically, zircon crystals have higher ZrO2 values in the core whereas HfO2 , UO2 , ThO2 increase at the peripheries of zoned crystals of the two-mica granite. Zircon of two-mica granite contains high HfO2 , UO2 , ThO2 and CaO contents but low Sc2 O3 content. HfO2 is not detected in zircon of microgranite. TiO2 in zircon of two-mica granite and bostonite dikes is under detection limits. REEs are not recorded in zircon of the studied intrusive rocks
Dike
Granitic rock
Cite
Citations (11)
Cite
Citations (23)
NIST
Trace element
Cite
Citations (1,551)
Table S1: Location information for new detrital zircon samples. Table S2: New zircon U-Pb and trace element data. Table S3: Compiled zircon U-Pb and trace element data. Figure S1: Comparison of Ce anomaly (A) and Eu anomaly (B) of zircons calculated using the method of Onuma et al. (1968) and traditional methods. Figure S2: Summary figures from zircon trace element compilation.
Trace element
Table (database)
Cite
Citations (0)
In this article we present a compilation of U-Pb zircon ages of the whole Xolapa terrane in coastal southern Mexico (dataset 1) as a curved line, obtained from plotting individual zircon grains versus its corresponding age. We identified five low-slope segments of the curved line, each one assigned to a high zircon-production (or preservation) event (HZE). Crystallization temperatures (CT) from Ti-in-zircon geothermometer data on Xolapa rocks were estimated separately from individual zircon grains (dataset 2), in order to compare CT ranges corresponding to each HZE identified. Datasets 1 and 2 are discussed for tectonic implications in the research article "The opening and closure of the Jurassic-Cretaceous Xolapa basin, southern Mexico" Peña-Alonso et al., 2017.
Cite
Citations (3)