Post-Miocene shortening pictured by magnetic fabric across the Zagros-Makran syntaxis (Iran)
C Aubourg, B Smith, H Bakhtari, N Guya, A Eshragi, S Lallemant, M Molinaro, X Braud, S Delaunay, 2004. "Post-Miocene shortening pictured by magnetic fabric across the Zagros-Makran syntaxis (Iran)", Orogenic curvature: Integrating paleomagnetic and structural analyses, Aviva J. Sussman, Arlo B. Weil
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We investigated the magnetic fabric of weakly deformed sedimentary rocks from the Zagros-Makran syntaxis. This syntaxis divides the active continental collision in the Zagros Mountains and the subduction in the Makran region of the Arabian Plate by the Iran block. We concentrated sampling for anisotropy of magnetic susceptibility (74 sites, about 1000 cores) in Miocene-Pliocene synorogenic clastics from Zagros and in Eocene to Pliocene flysch from Makran. In Zagros, the magnetic fabric is essentially intermediate (magnetic foliation parallel to bedding, magnetic lineation of tectonic origin), except in folds where tectonic magnetic foliation can develop. The degree of anisotropy is low (P′ < 1.1), and the shape of the anisotropy of magnetic susceptibility (AMS) ellipsoid is oblate to triaxial. We propose that AMS records a tectonic imprint related to the development of a layer of parallel shortening prior to folding. In the northern part of Makran, we propose that AMS in distal flysch preserves a magnetic foliation related to the deposition of turbidites. This magnetic foliation is oblique to bedding by ~20°, and such imbrication can be used to trace sedimentary flow. The degree of anisotropy is low (P′ < 1.1), and the shape of the AMS ellipsoid is oblate. In addition, the tectonic origin of magnetic lineation is not proved in these flysches. In the southern part of Makran, the clastics display an intermediate magnetic fabric, characterized by a low degree of anisotropy (P′ < 1.06) and an oblate to prolate AMS ellipsoid. Given the tectonic magnetic fabrics obtained from Zagros and South Makran, we inferred a shortening direction and compare this shortening direction to P-axes of centroid moment tensor (CMT) foci in the Zagros belt, which reflect the present day shortening direction in the basement of the Zagros. Both the AMS shortening direction and P-axes show an arcuate pattern, miming the shape of the Fars Arc of Zagros and the reentrant of the syntaxis. The disparity between P-axes and AMS shortening directions in the syntaxis may be related to decoupling of basement and cover strata. We combine our data with other structural elements to develop a model in which Oman acts as an indentor during the convergence of the Arabian Plate since the Miocene.