Clay mineral assemblage of the Middle Triassic-Lower Jurassic mudrocks from western-central Mediterranean Alpine Chains

The Middle Triassic to Lowermost Jurassic mudrocks from continental redbeds of the western-central Mediterranean region (Sicily, Calabria, Betic Cordillera and Rif) have been analyzed in order to reveal the mineralogical composition of the sediments and their thermal/burial history within the geological evolution of the Mediterranean area; the redbeds studied in this work have a palaeogeographic and geodynamic importance at the regional scale. The studied samples are characterized by the presence of abundant clay minerals; subordinately are present significant amounts of quartz and Fe-oxides (hematite or goethite), and minor concentrations of feldspars, calcite and dolomite. The <2 μm grain-size fraction of the samples is mostly composed by illite prevailing on illite-smectite mixed layers, kaolinite and chlorite. The proportions of illite in I-S mixed layers are in a range of 70-90 % of I/S (R>1), with an illite crystallinity value (IC) of 0.6-0.7° Δ2θ CuKα; these data suggest that the temperature experienced by the Mediterranean successions is in the range 100-150 °C. Thus the diagenetic/tectonic evolution should correspond to a lithostatic/tectonic loading of about 4-5 km.