International Journal of Earth Sciences

, Volume 106, Issue 1, pp 255–268

Constraining the alteration history of a Late Cretaceous Patagonian volcaniclastic bentonite–ash–mudstone sequence using K–Ar and 40Ar/39Ar isotopes

Original Paper

DOI: 10.1007/s00531-016-1315-2

Cite this article as:
Warr, L.N., Hofmann, H. & van der Pluijm, B.A. Int J Earth Sci (Geol Rundsch) (2017) 106: 255. doi:10.1007/s00531-016-1315-2

Abstract

Smectite is typically considered unsuitable for radiometric dating, as argon (40Ar) produced from decay of exchangeable potassium (40K) located in the interlayer sites can be lost during fluid–rock interaction and/or during wet sample preparation in the laboratory. However, age analysis of Late Cretaceous Argentinian bentonites and associated volcaniclastic rocks from Lago Pellegrini, Northern Patagonia, indicates that, in the case of these very low-permeability rocks, the radioactive 40Ar was retained and thus can provide information on smectite age and the timing of rock alteration. This study presents isotopic results that indicate the ash-to-bentonite conversion and alteration of the overlying tuffaceous mudstones in Northern Patagonia was complete ~13–17 my after middle Campanian sedimentation when the system isotopically closed. The general absence of illite in these smectite-rich lithologies reflects the low activity of K and the low temperature (<60 °C) of the formation waters that altered the parent ash.

Keywords

Smectite age dating K–Ar and 40Ar/39Ar isotopes Cretaceous ash Bentonite Tuffaceous mudstone Detrital mica Neuquén Basin Argentina 

Supplementary material

531_2016_1315_MOESM1_ESM.xlsx (25 kb)
Supplementary material 1 (XLSX 26 kb)
531_2016_1315_MOESM2_ESM.xlsx (34 kb)
Supplementary material 2 (XLSX 34 kb)
531_2016_1315_MOESM3_ESM.xlsx (150 kb)
Supplementary material 3 (XLSX 151 kb)

Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  • L. N. Warr
    • 1
  • H. Hofmann
    • 2
  • B. A. van der Pluijm
    • 3
  1. 1.Institute of Geography and GeologyErnst-Moritz-Arndt-University GreifswaldGreifswaldGermany
  2. 2.LörrachGermany
  3. 3.Department of Earth and Environmental SciencesUniversity of MichiganAnn ArborUSA

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