Evidence of phyllosilicate alteration processes and clay mineral neoformation promoted by hydrothermal fluids in the Padul Fault area (Betic Cordillera, SE Spain) Abad, Isabel Nieto García, Fernando Reolid Pérez, Matias Jiménez-Millán, Juan Cataclasite Chlorite Nanoscale Talc Thermometry Zn Acknowledgements We acknowledge the technical and human support provided by CICT of Universidad de Ja´en (UJA, MINECO, Junta de Andalucía, FEDER). Cecilia de la Prada is especially recognized for helping with the HRTEM work. The access to the HAADF Thermo Fisher Scientific TALOS F200X microscope was facilitated by the Centro de Instrumentaci´on Científica of the Universidad de Granada. The authors are indebted to responsible of the JUMA Quarry and El Mill´on Quarry. Thanks are extended to B. Dubacq and an anonymous reviewer for their critical reviews and helpful comments and suggestions. Supplementary data to this article can be found online at https://doi. org/10.1016/j.clay.2022.106669. Funding This research was supported by the project PGC2018-094573-B-I00 from the MCIU-AEIFEDER and the research groups RNM-325, RNM-200 and RNM-179 of the Junta de Andalucía. Geochemical changes and authigenic clays were detected in the fault rocks of the Padul Fault. An enrichment from the protolith to the ultracataclasites in Si, Al, Fe, Ca, Ti and also Zn but an impoverishment in Mg was detected. Although the protolith (dolostones) and fault rocks are mostly composed of carbonates, the fault rocks are also characterized by the presence of fine-grained clays in the matrix (mainly chlorite and Mg-rich biotite, but also smectite and punctually talc). Neither chlorite nor talc were detected in the protolith. The application of chlorite thermometry gives temperatures around 140–220 °C for chlorites lamellae located on the fault plane. These chlorites are compositionally homogeneous, whereas the chlorites detected in the cataclasites are more variable, although both of them are Mg-rich and have almost no Fe. As well, chlorites from the cataclasites usually include Zn in their composition and, as observed at nanoscale, they are genetically related to biotites, which come from the protolith. Talc grains (< 1 μm) are always found between dolomite and calcite. These observations point to clay mineral reactions in the fault rocks as the chlorite and talc precipitation promoted by circulation of fault-controlled hydrothermal fluids close to 200 °C. Other clays such as smectite are the result of the final step of the hydrothermal activity in the fault. The identification of authigenic clay minerals, which cause weakening mechanisms, is consistent with the geodetic characterization of the Padul Fault, which plays an important role in aseismic deformation. 2022-10-13T11:52:50Z 2022-10-13T11:52:50Z 2022-09-08 info:eu-repo/semantics/article I. Abad et al. Evidence of phyllosilicate alteration processes and clay mineral neoformation promoted by hydrothermal fluids in the Padul Fault area (Betic Cordillera, SE Spain). Applied Clay Science 230 (2022) 106669 [https://doi.org/10.1016/j.clay.2022.106669] https://hdl.handle.net/10481/77300 10.1016/j.clay.2022.106669 eng http://creativecommons.org/licenses/by-nc-nd/4.0/ info:eu-repo/semantics/openAccess Attribution-NonCommercial-NoDerivatives 4.0 Internacional Elsevier