Strain indicators and magnetic fabric in intraplate fault zones: Case study of Daroca thrust, Iberian Chain, Spain

Anisotropy of magnetic susceptibility (AMS) has been applied to the study of shallow fault zones, although
interpretation of the results requires establishing clear relationships between petrofabric and magnetic features,
magnetic behaviour of fault rocks, and an extensive knowledge of P-T conditions. In this work, we demonstrate
that magnetic methods can be applied to the study of heterogeneous fault zones, provided that a series of
requisites are met. A major fault zone within the Iberian plate (Daroca thrust), showing transpressional movements
during Cenozoic time was chosen for this purpose, because of the exceptional outcrops of fault gouge and
microbreccia and its relevance within the context of the northeastern Iberian Plate. Magnetic fabrics were
analysed and the results were compared with foliation and S-C structures measured within the fault zone. Clay
mineral assemblages suggest maximum burial depths shallower than 2 km (< 60–70 °C) for fault rocks in the
footwall of the Daroca thrust. The orientation of the AMS axes is consistent with mesostructural strain indicators:
kmin parallels the mean pole to S, or it is intermediate between S and C poles; kmax is oriented at a high angle
(nearly orthogonal in overall) to the transport direction, which can be explained from both deformational and
mineralogical controls. Both magnetic fabrics and kinematic indicators are consistent with a reverse movement
for most of the fault zone.