Journal of Earth Science

, Volume 29, Issue 2, pp 416–426 | Cite as

Occurrence of Excess 40Ar in Amphibole: Implications of 40Ar/39Ar Dating by Laser Stepwise Heating and in vacuo Crushing

  • Rong-Guo Hu
  • Xiu-Juan Bai
  • Jan Wijbrans
  • Fraukje Brouwer
  • Yi-Lai Zhao
  • Hua-Ning Qiu
Isotope Geochemistry


The joint methods of 40Ar/39Ar laser stepwise heating and in vacuo crushing have been applied to date amphiboles from the North Qaidam ultra-high pressure metamorphic amphibolites. Two amphibole samples analyzed by laser heating yielded saddle-shaped age spectra with total gas ages of 574.5±2.5 and 562.5±2.5 Ma. These ages are much older than the reported zircon U-Pb ages (∼495 Ma) from Yuka eclogite, indicating the presence of excess 40Ar. In order to decipher the occurrence of excess 40Ar and constrain the age of amphibolite-facies retrogression, two duplicate amphibole samples were further employed for 40Ar/39Ar in vacuo crushing analyses. Both samples exhibit similar monotonically declining release spectra, which are characterized by rapid decline of anomalously old apparent ages in the early steps. The data of the late steps yielded concordant apparent ages with plateau ages of 460.9±1.2 and 459.6±1.8 Ma. We interpret that gases released in the early steps derive from the significant excess 40Ar containing secondary fluid inclusions (SFIs) due to their distribution characteristics along cracks leading to be easily extracted, whereas those released in the later steps represent the contribution of the small primary fluid inclusions (PFIs).

Key words

40Ar/39Ar dating in vacuo crushing amphibole fluid inclusions 



We thank two anonymous reviewers for their comments that substantially improved this manuscript. We also sincerely thank Mr. Roel Van Elsas, Mrs. Wynanda Koot, Mr. Onno Postma, Mr. Arie Bikker, and Mr. Wim van der Plas from the VU Amsterdam, for their kind help in mineral separation, thin section preparation, and technical support for 40Ar/39Ar analyses. This work was funded by the National Natural Science Foundation of China (Nos. 41703054, 41503053), the Guangxi Natural Science Foundation Program (Nos. 2016GXNSFCA380022, 2014GXNSFBA118231) and the Chinese Academy of Sciences-Royal Netherlands Academy of Arts and Sciences Joint PhD Training Programme (No. O8PhD-08). The final publication is available at Springer via

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Copyright information

© China University of Geosciences and Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.College of Earth Sciences, Guangxi Key Laboratory of Hidden Metallic Ore Deposits ExplorationGuilin University of TechnologyGuilinChina
  2. 2.Geology & Geochemistry Cluster, Department of Earth SciencesVU AmsterdamAmsterdamThe Netherlands
  3. 3.Key Laboratory of Tectonics and Petroleum Resources, Ministry of EducationChina University of GeosciencesWuhanChina
  4. 4.State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of GeochemistryChinese Academy of SciencesGuangzhouChina

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