Multidisciplinary approach to constrain kinematics of fault zones at shallow depths: a case study from the Cameros–Demanda thrust (North Spain)

Determining transport direction in thrusts is one of the main issues to study deformation and to achieve reliable balanced cross-sections reconstruction of inverted basins and thrust systems. Anisotropy of Magnetic Susceptibility provides a tool to study deformation in fault rocks through the relationships between the magnetic susceptibility ellipsoid and deformational structures. The Cameros-Demanda Thrust (N Spain) shows a relatively simple history, with an average N-directed movement during the Cenozoic, and provides the possibility of determining the relationships between magnetic fabrics and transport directions in thrusts. The outcropping rocks are Mesozoic limestones in the hangingwall of the main thrust and Cenozoic conglomerates and Albian sandstones and coal in its footwall. Illite crystallinity and organic matter maturity indicate P-T conditions on the order of....The study of AMS in fault rocks (more than 400 samples distributed in 25 sites with fault gouge, breccia and microbreccia) in the Cameros thrust and its comparison with kinematic indicators (foliation, S/C structures and slickenside striations) indicates, in spite of the a priori simple relationships inferred from thrust geometry, a complex history of movements, changing from top-to-the-NW to top-to-the-NE along the history of Cenozoic thrusting. The transport direction is either oblique to the magnetic lineation and perpendicular to the strike of magnetic foliation, and can be checked with shear structures observed in thin sections and other kinematic indicators. The results obtained indicate that AMS can give clues about the transport direction in thrusts depending on the particular structures developed in each studied area.