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Using Th-U-Pb geoch...
Using Th-U-Pb geochronology to extract crystallization ages of Paleozoic metamorphic monazite contaminated by initial Pb
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- Barnes, C. J. (författare)
- Polish Acad Sci, Inst Geol Sci, Krakow, Poland.;AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland.
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- Majka, Jaroslaw (författare)
- Uppsala universitet,Mineralogi, petrologi och tektonik,AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland.
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- Jeanneret, Pauline (författare)
- Uppsala universitet,Mineralogi, petrologi och tektonik
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- Ziemniak, G. (författare)
- AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland.;Univ Wroclaw, Inst Geol Sci, Wroclaw, Poland.
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- Kooijman, Ellen (författare)
- Naturhistoriska riksmuseet,Enheten för geovetenskap,Vegacenter,Swedish Museum Nat Hist, Dept Geosci, Stockholm, Sweden.
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- Kosminska, K. (författare)
- AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland.
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- Kielman-Schmitt, Melanie, 1988- (författare)
- Naturhistoriska riksmuseet,Enheten för geovetenskap,Vegacenter,Swedish Museum Nat Hist, Dept Geosci, Stockholm, Sweden.
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- Schneider, D. A. (författare)
- Univ Ottawa, Dept Earth & Environm Sci, Ottawa, ON, Canada.
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Majka, Jarek (författare)
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Polish Acad Sci, Inst Geol Sci, Krakow, Poland;AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland. Mineralogi, petrologi och tektonik (creator_code:org_t)
- Elsevier, 2021
- 2021
- Engelska.
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Ingår i: Chemical Geology. - : Elsevier. - 0009-2541 .- 1872-6836. ; 582
- Relaterad länk:
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Abstract
Ämnesord
Stäng
- Geochronology of Th-rich minerals is advantageous as it allows use of three isotopic systems (i.e., Pb-206/U-238, Pb-207/U-235, and Pb-208/Th-232) for accurate data assessment. The Pb-208/Th-232 system is especially advantageous in cases where the dated mineral includes an initial Pb component, as Pb-208/Th-232 is the least sensitive to the effects of initial Pb amongst the three systems. This benefit is demonstrated with monazite from a white mica schist of the Tsakkok Lens, Scandinavian Caledonides, where three distinct generations of Paleozoic monazite (Mnzsingle bondI, Mnz-II, Mnz-III) are recognized and dated using laser ablation inductively coupled mass spectrometry. The generations are interpreted to represent monazite crystallization in high-pressure conditions (Mnzsingle bondI), followed by lower-pressure monazite growth (Mnz-II), and likely dissolution-reprecipitation of the pre-existing monazite (Mnz-III). The results are compared in Tera-Wasserburg, Wetherill, and Th-U-Pb concordia space for each monazite generation. In both Tera-Wasserburg and Wetherill space, the data are all discordant and indicate an initial Pb component in the monazite. The trend and magnitude of discordance due to initial Pb in Mnz-I and Mnz-II is generally controlled by UO2 content of the monazite, with higher UO2 equating to greater radiogenic Pb and a dampening of the initial Pb effect, which is most prominent in the Pb-207/U-235 system. For the same generations, initial Pb discordance of Pb-206/U-238 versus Pb-208/Th-232 is less apparent due to the insensitivity of Pb-208/Th-232. Mnz-III does not follow the initial Pb trends, likely due to disturbance of the chemical and isotopic systems during recrystallization. Additional discordance in Mnz-I and Mnz-II, which is not related to initial Pb, is recognized and increases with actinide content. The additional discordance may be due to Pb-mobilization in Mnz-I and Mnz-II domains and is revealed when utilizing the( 208)Pb/Th-232 system due to its insensitivity to initial Pb effects. Consequently, relying only on the U-Pb systems can lead to significant initial Pb overcorrections in Tera-Wasserburg or Wetherill concordia space and to calculations of erroneously young concordia dates. The Th-U-Pb concordia method, incorporating all three systems, does not require an initial Pb correction and, therefore, can account for the additional discordance. The Th-U-Pb concordia dates are interpretated as accurate crystallization ages for Mnz-I (484.7 +/- 1.1 Ma, MSWD: 1.4) and Mnz-II (474.7 +/- 1.2 Ma, MSWD: 1.9). The timing for Mnz-III formation is not well-resolved as it formed via result of dissolution-reprecipitation of the pre-existing monazite, likely under lower amphibolite- to greenschist-facies conditions.
Ämnesord
- NATURVETENSKAP -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)
- NATURAL SCIENCES -- Earth and Related Environmental Sciences -- Geology (hsv//eng)
- NATURVETENSKAP -- Geovetenskap och miljövetenskap -- Geokemi (hsv//swe)
- NATURAL SCIENCES -- Earth and Related Environmental Sciences -- Geochemistry (hsv//eng)
Nyckelord
- Scandinavian Caledonides
- Monazite
- Initial Pb contamination
- Pb mobilization
- LA-ICP-MS Th-U-Pb isotopic dating
- The changing Earth
Publikations- och innehållstyp
- ref (ämneskategori)
- art (ämneskategori)
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