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- Title
In search of lost time: Raman thermochronology of FC-1 zircon.
- Authors
Härtel, Birk; Enkelmann, Eva; Jonckheere, Raymond; Ludwig, Thomas; Krause, Joachim; Ratschbacher, Lothar
- Abstract
Translating thermochronological ages to geological models requires knowledge of the thermal sensitivity of the applied thermochronometer, i.e. the closure temperature or the partial annealing/retention zone. Zircon Raman dating is a thermochronometer that uses radiation-damage measurements and matched analyses of actinide contents in zircon. Experimental work placed its closure temperature at 330–370 °C for the internal ν2(SiO4) and ν3(SiO4) Raman bands at 439 and 1008 cm−1, and 260–310 °C for the external rotation (ER) band at 356 cm−1. However, experimental annealing models also predict partial radiation-damage annealing over a broad temperature range (> 500 °C). We test these closure temperatures by dating zircon from the U–Pb reference material FC-1. We matched Raman-based radiation-damage measurements with U and Th concentrations measured with a secondary ion mass spectrometer. The zircon Raman ages for the ν2, ν3, and ER bands are 942 ± 23 Ma (2 s), 978 ± 38 Ma, and 1033 ± 32 Ma. This is lower than the expected range of 1040–1080 Ma, between the apatite U–Pb (~ 490 °C) and zircon (U-Th)/He (ZHe; ~ 200 °C) ages. We discuss long-term, low-temperature annealing of radiation damage during protracted cooling of the sample as a cause of age reduction. This explanation fits both, experimental annealing models and zircon Raman data from other geological settings. Long-term, low-temperature annealing complicates the interpretation of standalone zircon Raman data. However, exploiting this effect by combining zircon Raman and ZHe dating on the same sample provides thermal-history information beyond that revealed by either of them.
- Subjects
ZIRCON; GEOLOGICAL modeling; RADIATION damage; MASS spectrometers; REFERENCE sources
- Publication
Contributions to Mineralogy & Petrology, 2024, Vol 179, Issue 1, p1
- ISSN
0010-7999
- Publication type
Article
- DOI
10.1007/s00410-023-02083-z