Illite crystallinity patterns in the Anti-Atlas of Morocco

Abstract

The low-grade metamorphism of the sedimentary cover of the Moroccan Anti-Atlas is investigated using Illite crystallinity (IC) method. More than 200 samples from three key areas (southwestern, central and eastern Anti-Atlas) have been taken from a maximum of different stratigraphic levels and have been analysed. The metamorphism is of low to very low degree throughout the southern flank of the Anti-Atlas. It increases from northeast to southwest. Whereas in the eastern Anti-Atlas diagenetic and anchizonal IC-values are predominant, in the western and central Anti-Atlas also epizonal IC-values are found. In every respective area the IC improves with stratigraphic age. At the scale of the entire Palaeozoic Anti-Atlas basin the IC correlates best with estimated paleo-overburden. However, burial metamorphism cannot be the cause even though considering missing sedimentary pile of Late Carboniferous age. The ‘abnormal’ paleo-geothermal gradient of 43–35 °C/km we evidenced for the Carboniferous is a true one, and has to be related to a basement sequence enriched in heat producing elements such as series of the West African Craton.

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Correspondence to Geoffrey M. H. Ruiz.

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Edtitorial handling: J. Mosar, S. Bucher

Manuscript received November 23, 2007. Revision accepted May 15, 2008

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Ruiz, G.M.H., Helg, U., Negro, F. et al. Illite crystallinity patterns in the Anti-Atlas of Morocco. Swiss J. Geosci. 101, 387–395 (2008). https://doi.org/10.1007/s00015-008-1267-z

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Keywords:

  • Anti-Atlas
  • low-grade metamorphism
  • Illite crystallinity
  • paleo-geothermal gradient
  • Carboniferous