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| Titel |
A novel approach to in-situ rutile petrochronology |
| VerfasserIn |
Ellen Kooijman, Matthijs Smit, Andrew Kylander-Clark |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250143695
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| Publikation (Nr.) |
 EGU/EGU2017-7442.pdf |
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| Zusammenfassung |
| Rutile petrochronology has become an increasingly important tool for deciphering the timing
and conditions of petrological processes. Rutile provides a reliable single-mineral
thermometer, capable of retaining temperature information during high and ultra-high
temperature metamorphism. Its HFSE contents can be used to investigate the geochemical
environment in which rutile crystallized. Most importantly, rutile strongly fractionates U/Pb
and enables U-Pb thermochronology in the intermediate temperature range. Here we present
a novel approach to using U-Pb thermochronology of rutile by exploring the use of Pb
as a diffusive species in kinetics-based thermometry. We performed high spatial
and analytical resolution micro-analysis of rutile by laser ablation multi-collector
ICPMS to constrain Pb diffusion profiles in rutile from high-grade metamorphic
rocks of the Western Gneiss Complex (WGC), Norway. The age and thermometric
results from this analysis are used to constrain a full thermal history from single
grains.
Millimeter-sized single crystals of rutile from a rutile-rich phlogopitite vein in eclogite
were mounted and polished to expose their geometric cores. The grains were analyzed in
transects using rectangular spots (c. 15x45 μm). This ensures ablation of a significant volume
while maintaining the required radial spatial resolution. The transects yielded well-defined
Pb diffusion profiles, with U-Pb ages ranging from c. 415 Ma in the cores to c.
380 Ma in the outermost rims (±2%, 2σ on individual spots). Diffusion zoning
length was used with well-established Pb diffusion parameters [1] to determine peak
temperature conditions following the approach of [2]. The result, c. 810 ± 25 ˚ C,
is consistent with 800 ± 25 ˚ C and c. 780 ˚ C estimated for the same sample
using conventional and Zr-in-rutile thermometry, respectively. The cooling history
that is reconstructed through age zoning analysis and diffusion modeling shows
remarkable consistency with that established for the WGC through decades of 40Ar/39Ar
dating.
The data presented here demonstrate that in-situ rutile U-Pb analysis yields reliable
and precise temperature and age information that can be combined to resolve full
thermal histories from single crystals. This novel approach to the toolbox of rutile
petrochronology has great potential for research into the tectonics and dynamics of the
lithosphere.
References
[1] Cherniak (2000) Contrib. Mineral. Petrol. 139. 198-207.
[2] Smit et al. (2013) J. Metamorph. Geol. 31. 339-358. |
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