Progressive, episodic deformation in the Mexican Fold-Thrust Belt (central Mexico): Evidence from isotopic dating of folds and faults

Elisa Fitz-Diaz, Peter Hudleston, Gustavo Tolson, Ben Van Der Pluijm

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46 Scopus citations


We used illite Ar/Ar dating to obtain absolute ages of folds and shear zones formed within the Mexican Fold-Thrust Belt (MFTB). The methodology takes advantage of illite dating in folded, clay-bearing layers and the ability to obtain accurate ages from small-size fractions of illite using encapsulated Ar analysis. We applied our approach to a cross-section that involves folded Aptian-Cenomanian shale-bentonitic layers interbedded with carbonates of the Zimapán (ZB) and Tampico-Misantla (TMB) Cretaceous basins in central-eastern Mexico. Basinal carbonates were buried by syn-tectonic turbidites and inverted during the formation of the MFTB in the Late Cretaceous. Results from folds and shear zones record different pulses of deformation within this thin-skinned orogenic wedge. Mineralogical compositions, variations in illite polytypes, illite crystallite size (CS), and Ar/Ar ages were obtained from several size fractions in limbs and hinges of the folds and in the shear zones. 1Md-illite polytype (with CS of 6-9 nm) dominates in two folds in the TMB while 2M1-illlite (with CS of 14-30 nm) dominates in the third fold, in the ZB, and in the fold/shear zone. From west (higher grade) to east (lower grade): Ar retention ages indicate shearing occurred at ~84 Ma in the westernmost shear zone, folding at ~82 Ma in the ZB with subsequent localized shearing at ~77 Ma, and Ar total gas ages constrain the time of folding at ~64 Ma on the west side of the TMB and ~44 Ma on the eastern edge. These results are consistent with the age and distribution of syn-tectonic turbidites and indicate episodic progression of deformation from west to east.

Original languageEnglish (US)
Pages (from-to)734-755
Number of pages22
JournalInternational Geology Review
Issue number6
StatePublished - Apr 26 2014


  • Ar/Ar dating
  • fold-thrust belt
  • illite
  • progressive deformation


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