Nanogeochronology of discordant zircon measured by atom probe microscopy of Pb-enriched dislocation loops
Isotopic discordance is a common feature in zircon that can lead to an erroneous age determination, and it is attributed to the mobilization and escape of radiogenic Pb during its post-crystallization geological evolution. The degree of isotopic discordance measured at analytical scales of ~10 µm of...
| Main Authors: | , , , , , , |
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| Format: | Journal Article |
| Published: |
2016
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| Online Access: | http://hdl.handle.net/20.500.11937/43560 |
| _version_ | 1848756731997323264 |
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| author | Peterman, E. Reddy, Steven Saxey, David Snoeyenbos, D. Rickard, William Fougerouse, Denis Kylander-Clark, A. |
| author_facet | Peterman, E. Reddy, Steven Saxey, David Snoeyenbos, D. Rickard, William Fougerouse, Denis Kylander-Clark, A. |
| author_sort | Peterman, E. |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | Isotopic discordance is a common feature in zircon that can lead to an erroneous age determination, and it is attributed to the mobilization and escape of radiogenic Pb during its post-crystallization geological evolution. The degree of isotopic discordance measured at analytical scales of ~10 µm often differs among adjacent analysis locations, indicating heterogeneous distributions of Pb at shorter length scales. We use atom probe microscopy to establish the nature of these sites and the mechanisms by which they form. We show that the nanoscale distribution of Pb in a ~2.1 billion year old discordant zircon that was metamorphosed c. 150 million years ago is defined by two distinct Pb reservoirs. Despite overall Pb loss during peak metamorphic conditions, the atom probe data indicate that a component of radiogenic Pb was trapped in 10-nm dislocation loops that formed during the annealing of radiation damage associated with the metamorphic event. A second Pb component, found outside the dislocation loops, represents homogeneous accumulation of radiogenic Pb in the zircon matrix after metamorphism. The (207)Pb/(206)Pb ratios measured from eight dislocation loops are equivalent within uncertainty and yield an age consistent with the original crystallization age of the zircon, as determined by laser ablation spot analysis. Our results provide a specific mechanism for the trapping and retention of radiogenic Pb during metamorphism and confirm that isotopic discordance in this zircon is characterized by discrete nanoscale reservoirs of Pb that record different isotopic compositions and yield age data consistent with distinct geological events. These data may provide a framework for interpreting discordance in zircon as the heterogeneous distribution of discrete radiogenic Pb populations, each yielding geologically meaningful ages. |
| first_indexed | 2025-11-14T09:16:52Z |
| format | Journal Article |
| id | curtin-20.500.11937-43560 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| last_indexed | 2025-11-14T09:16:52Z |
| publishDate | 2016 |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-435602017-09-13T13:39:38Z Nanogeochronology of discordant zircon measured by atom probe microscopy of Pb-enriched dislocation loops Peterman, E. Reddy, Steven Saxey, David Snoeyenbos, D. Rickard, William Fougerouse, Denis Kylander-Clark, A. Isotopic discordance is a common feature in zircon that can lead to an erroneous age determination, and it is attributed to the mobilization and escape of radiogenic Pb during its post-crystallization geological evolution. The degree of isotopic discordance measured at analytical scales of ~10 µm often differs among adjacent analysis locations, indicating heterogeneous distributions of Pb at shorter length scales. We use atom probe microscopy to establish the nature of these sites and the mechanisms by which they form. We show that the nanoscale distribution of Pb in a ~2.1 billion year old discordant zircon that was metamorphosed c. 150 million years ago is defined by two distinct Pb reservoirs. Despite overall Pb loss during peak metamorphic conditions, the atom probe data indicate that a component of radiogenic Pb was trapped in 10-nm dislocation loops that formed during the annealing of radiation damage associated with the metamorphic event. A second Pb component, found outside the dislocation loops, represents homogeneous accumulation of radiogenic Pb in the zircon matrix after metamorphism. The (207)Pb/(206)Pb ratios measured from eight dislocation loops are equivalent within uncertainty and yield an age consistent with the original crystallization age of the zircon, as determined by laser ablation spot analysis. Our results provide a specific mechanism for the trapping and retention of radiogenic Pb during metamorphism and confirm that isotopic discordance in this zircon is characterized by discrete nanoscale reservoirs of Pb that record different isotopic compositions and yield age data consistent with distinct geological events. These data may provide a framework for interpreting discordance in zircon as the heterogeneous distribution of discrete radiogenic Pb populations, each yielding geologically meaningful ages. 2016 Journal Article http://hdl.handle.net/20.500.11937/43560 10.1126/sciadv.1601318 fulltext |
| spellingShingle | Peterman, E. Reddy, Steven Saxey, David Snoeyenbos, D. Rickard, William Fougerouse, Denis Kylander-Clark, A. Nanogeochronology of discordant zircon measured by atom probe microscopy of Pb-enriched dislocation loops |
| title | Nanogeochronology of discordant zircon measured by atom probe microscopy of Pb-enriched dislocation loops |
| title_full | Nanogeochronology of discordant zircon measured by atom probe microscopy of Pb-enriched dislocation loops |
| title_fullStr | Nanogeochronology of discordant zircon measured by atom probe microscopy of Pb-enriched dislocation loops |
| title_full_unstemmed | Nanogeochronology of discordant zircon measured by atom probe microscopy of Pb-enriched dislocation loops |
| title_short | Nanogeochronology of discordant zircon measured by atom probe microscopy of Pb-enriched dislocation loops |
| title_sort | nanogeochronology of discordant zircon measured by atom probe microscopy of pb-enriched dislocation loops |
| url | http://hdl.handle.net/20.500.11937/43560 |