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| Titel |
Single grain detrital rutile U-Pb chronology: a key provenance tracer |
| VerfasserIn |
Laura Bracciali, Randall R. Parrish, Yani Najman, Matthew S. A. Horstwood, Daniel J. Condon |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250080616
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| Zusammenfassung |
| Rutile is an accessory mineral commonly found in the heavy mineral suite of detrital rocks
due to its stability during the sedimentary processes. This mineral originates mainly in
medium- to high-grade metamorphic and some igneous rocks and similarly to zircon and
other U-bearing minerals can be dated by the U-Pb method. Nevertheless, there are still very
few applications of U-Pb dating of rutile to provenance studies, likely because it usually has a
lower U content compared to zircon (which in turn leads to lower radiogenic Pb content
limiting measurement quality) and it can contain a relatively large proportion of common
(non radiogenic) Pb. In addition, there is a scarcity of widely available good quality natural
rutile reference materials that can be used to assess reproducibility and accuracy of the dating
technique.
We have addressed these issues and characterized two ~ 1.8 Ga rutile reference materials
(namely Sugluk-4 and PCA-S207 from granulite facies belts of the Canadian Shield) by
SEM, trace elements, U-Pb ID-TIMS, and intra-grain and inter-grain U-Pb LA-MC-ICP-MS
analysis. LA-U-Pb data (n ~ 500 for each of the two reference materials, collected using a
New Wave Research 193 nm wavelength laser ablation system coupled to a Nu Plasma HR
mass spectrometer) have a reproducibility of 206Pb/238U and 207Pb/206Pb of ~2–4% (at the
2Ïă level), which is only modestly worse than long-term data for multiple zircon standards,
this being due to the real variation in measured values arising from limited Pb loss, age
variation related to cooling, and common Pb variability. The analytical measurement of
rutile U-Pb data is rapid, allows high spatial resolution (the laser sampling protocol
employs a 50 or 35 μm static spot) and does not include common Pb correction
[1].
We have applied our refined method to constrain provenance of rutile from modern
drainages from British Columbia and the eastern Himalaya (with rutile ages as young as
75% of all rutile grains in a sediment; unsuccessful analyses are due to poor
quality rutiles with massive common Pb and/or U contents |
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