163129 20251009145936.0 doi 10.1007/s00531-025-02530-1 sideral 145616 ART-2025-145616 eng Simón-Muzás, Ana (orcid)0000-0001-5824-5367 Secondary precipitation of Fe–Ti oxides as a source for strongly changing magnetic properties in ancient volcanic rocks (Cadí Basin, Pyrenees) 2025 Abstract Strong changes of magnetic properties (magnetic susceptibility and natural magnetic remanence) affecting large volumes of rocks can be conditioned by a series of factors, including circulation of hydrothermal fluids or meteoric waters, often favored by the primary porosity of the rock or pervasive fracturing. In the Late Carboniferous-Permian Cadí Basin, in the Eastern Pyrenees, there are volcanic rocks that show a unique pattern of magnetic anomalies up to 200 nT in amplitude revealing a heterogeneous distribution of their magnetic properties. To unravel the origin of these anomalies, we performed a detailed study of the magnetic properties of the volcanic and volcaniclastic rocks, combined with magnetic surveying and analysis of brittle structures. The results indicate that the origin of the strong variations in the magnetic properties is linked to: (i) lithological changes within the volcanic series, and (ii) the inhomogeneous secondary precipitation of ferromagnetic minerals. As a result of these secondary processes, magnetic fabrics do not reliably record either the volcanic paleoflow or the deformation imprint. The mineralogical composition can be interpreted as the result of a strong hydrothermal alteration that took place during early diagenetic stages, which was also responsible for the neoformation of magnetite crystals with variable titanium content. Random fluid circulation during the Late-Variscan stage could be the origin of these strong variations in magnetic properties. Graphical Abstract Access copy available to the general public Unrestricted info:eu-repo/grantAgreement/ES/AEI/PID2019-108753GB-C22 info:eu-repo/grantAgreement/ES/MICINN/FPU19-02353 info:eu-repo/grantAgreement/ES/MICINN/PID2020-114273GB-C22 info:eu-repo/grantAgreement/ES/MICIU /PID2023-148256NB-I00 info:eu-repo/semantics/openAccess by https://creativecommons.org/licenses/by/4.0/deed.es info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion Casas-Sainz, Antonio M. Universidad de Zaragoza (orcid)0000-0003-3652-3527 Soto, Ruth Oliva-Urcia, Belén Universidad de Zaragoza (orcid)0000-0003-1563-6434 2000 428 Universidad de Zaragoza Dpto. Ciencias de la Tierra Área Geodinámica Interna 114, 5 (2025), 959-978 Int. j. earth sci. International Journal of Earth Sciences 1437-3254 5640980 http://zaguan.unizar.es/record/163129/files/texto_completo.pdf Versión publicada 2498626 http://zaguan.unizar.es/record/163129/files/texto_completo.jpg?subformat=icon icon Versión publicada oai:zaguan.unizar.es:163129 articulos driver 2025-10-08-12:59:46 ARTICLE