MAGNETIC FABRICS OF TERTIARY SANDSTONES FROM THE ARC-OF-FARS (EASTERNZAGROS, IRAN)

An analysis of magnetic fabric (45 sites, 514 samples) has been perfor med in folded but apparently not penetratively deformed Mio-Pliocene s edimentary rocks (mainly sandstones) from the Arc of Fars (Eastern Zag ros, Iran). Different types of magnetic fabrics and shapes of suscepti bility ellipsoids were observed from an oblate form reflecting a sedim entary fabric to a prolate form signifying a magnetic lineation of tec tonic origin. Classically in such weakly deformed sedimentary rocks th e magnetic lineation is perpendicular to the shortening direction and is interpreted as recording a pre-folding layer-parallel shortening. I n the studied area, the trends of the magnetic lineation show two clus ters oriented ENE-WSW and WNW-ESE. To a first approximation, the magne tic lineation follows the bending of the fold trend. However, a quite systematic obliquity is observed. According to regional geology and to other considerations arising from the magnetic analysis, we consider that the tectonic transport direction is NNW-SSE. The arc pattern obse rved in the fold and magnetic lineation trends may result either from an inherited structural framework or from post-folding clockwise rotat ions or both. In any case, our data rule out any interpretation of the whole Arc of Fars as resulting from the superimposition of two non-co axial folding events. (C) 1998 Elsevier Science B.V. All rights reserv ed.