The Ponga Unit lies in the core of the Cantabrian/Asturian arc, a thrust system which was emplaced and then noncoaxially refolded during the Variscan Orogeny. Alternative models for thrust system geometry prior to refolding of the Ponga Unit have been proposed. Although the Ponga Unit becomes populated with steeply plunging folds under each model, the alternative models imply differing kinematic histories for these folds. Paleomagnetic data were acquired from 22 sites in grey and red Carboniferous limestones around these folds in order to determine the rotational histories of the structures and hence to identify the appropriate geological model for initial thrust system geometry. Low anisotropy of magnetic susceptibility indicated that the samples were suitable for rigid-body rotation studies. Four remanence components were identified on stepwise demagnetization: A very low temperature, randomly orientated component V; a low-temperature component L present between 50¿C and 200¿C (64/349, α95=4.4¿), clustered around the Recent field in geographic coordinates; an intermediate-temperature component I present between 200¿C and 400--600¿C, of reverse polarity and shallow inclination and showing significant between-site dispersion; and a high-temperature component H (30/342, α95=21¿), lying close to the Eocene reference direction in geographic coordinates.

The I component fails a fold test based upon a first deformation phase (D1) hanging wall anticline and is therefore a remagnetization. The I component consistently gives positive fold tests of the steeply plunging fold structures when the structures are unfolded about their plunging hinges. This demonstrates that these folds result from north-south shortening of essentially homoclinal westerly dipping D1 hanging wall ramps and that alternative models involving steeply dipping interference folds arising from complex hanging wall deformation during D1 are invalid. A partial restoration of the thrust system based on the former model with the paleomagnetic data pinned to a calculated Stephanian reference direction shows that the thrust front was approximately north-south in trend in the Ponga Unit, as it was farther south in the Esla Unit, where anticlockwise rotations and destral wrench faulting have subsequently occurred. The data also record a tilt to the north of up to 30¿, which has occurred incrementally since the end of Variscan deformation. ¿ American Geophysical Union 1995.