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It is ∼100–250 km wide, thinning to the southeast and dominated by Cretaceous carbonates (Fitz-Díaz et al., 2011a; Guzmán and de Cserna, 1963).
The study area spans four Cretaceous paleogeographical areas: the Zimapán and Tampico-Misantla Basins and the Valles–San Luis Potosi and El Doctor Platforms.
By combining newly determined ages of illitization in folds with new paleomagnetic results in Mexico’s central Sierra Madre Oriental, this study demonstrates the ability to associate a radiometric age with synfolding remagnetizations.
Extensive work has shown that many carbonates around the world have been remagnetized (Jackson and Swanson-Hysell, 2012; Mc Cabe and Elmore, 1989; Van der Voo and Torsvik, 2012), highlighting the potentially wide-scale application of this approach.
The absolute age of folds was determined by clay grain-size separation, illite polytype characterization, and Ar dating of multiple size fractions (Fitz-Díaz and van der Pluijm, 2013; Haines and van der Pluijm, 2008).
Ages of thrusting were determined for the Tolimán Sequences (83.5 ± 1.5 Ma) on the western edge of the study area, the western and eastern Zimapán Basin (82 ± 0.5 Ma and 76.5 ± 1.0 Ma, respectively), and the western and eastern Tampico-Misantla Basin (64 ± 2.0 Ma and 43.5 ± 0.5 Ma, respectively); see Figure 2 for details (Fitz-Díaz et al., 2014).
From the structural point of view, the Sierra Madre Oriental is an east-northeast–verging thin-skinned fold-thrust belt, also known as the Mexican fold-thrust belt.Prior to this study, the common way to date a remagnetization event was qualitatively, through comparison of a determined magnetic direction to the apparent polar wander path of the region.In deformed areas, the age range of the remagnetization episode can be estimated relative to folding, through application of the paleomagnetic fold test (Facer, 1983). (2008) dated remagnetization events in the Cantabrian-Asturian Arc (northwestern Spain) by applying Ar/Ar dating to clays collected from the area.For example, during illitization, smectite transforms to illite, releasing Fe as temperatures increase with burial (Altaner and Ylagan, 1997). Thus, while the growth of magnetite has been well studied, dating of remagnetization events remains a challenge; the latter provided the motivation for this study.The growth of magnetite into a stable single-domain structure allows a remanent magnetization to be acquired, resulting in a chemically remagnetized unit (Hirt et al., 1993; Mc Cabe et al., 1989). (1998) presented evidence of a strong or detectable chemical remagnetization in the limestone-marl sequences of their study area, the Vocontian Trough (southeastern France). The occurrence of illite is associated with chemically remagnetized rocks in these studies, and the presence of smectite is associated with primary magnetizations or comparatively weaker chemical remagnetizations. Illitization from smectite or illite precursors is common in naturally deformed rocks (e.g., Vrolijk and van der Pluijm, 1999), offering the potential for radiometric dating of deformation (van der Pluijm et al., 2001).
The ability to successfully date mesoscopic folds made this an ideal area to test the feasibility of absolute dating of synfolding remagnetizations.