Implications of illite X-ray diffraction characteristics and K–Ar dating for the tectonics of Mallorca (Spain)

A pre-tectonic thermal event from the early Cretaceous, marked by a K–Ar age of 133–140 Ma and palaeotemperatures of 180–200°C, was identified in the Serra de Tramuntana of Mallorca using illite X-ray diffraction (XRD) characteristics and dating. This event reflects an extremely high geothermal gradient at the end of Mesozoic extension, predating the Oligocene–Miocene Alpine orogeny that shaped the mountain range. The study analyzed 16 samples from two outcrops, employing XRD, microscopy, microanalysis, and K–Ar dating on clay fractions. Pure volcanic rock samples yielded consistent ages, while contaminated samples confirmed the Cretaceous origin of the thermal event. Maximum palaeotemperatures during later tectonic burial were estimated to be below 250°C, preserving Cretaceous illite XRD features that indicate conditions near the diagenesis/anchimetamorphism boundary.

Środoń, J., Szczerba, M., & Bojanowski, M. J. (2025). Implications of illite X-ray diffraction characteristics and K–Ar dating for the tectonics of Mallorca (Spain). Clay Minerals, 60(3), 259–272. https://doi.org/10.1180/clm.2025.10014