Emplacement and Deformation of Mesozoic Gabbros of the High Atlas (Morocco): Paleomagnetism and Magnetic Fabrics. Issue 12 (13th December 2017)

• Record Type: Journal Article
• Authors: Calvín, P.; Ruiz‐Martínez, V. C.; Villalaín, J. J.; Casas‐Sainz, A. M.; Moussaid, B.
• Is Part Of: Tectonics. Volume 36:Issue 12(2017)
• Page Start: 3012
• Page End: 3037
• Publication Date: 2017-12-13
• Subjects: gabbro -- paleomagnetism -- magnetic fabric -- High Atlas -- Paleomagnetic restoration -- small circles; Geology, Structural -- Periodicals; 551.8
• DOI: 10.1002/2017TC004578
• Languages: English
• ISSNs: 0278-7407

Abstract

Abstract: A paleomagnetic and magnetic fabric study is performed in Upper Jurassic gabbros of the central High Atlas (Morocco). These gabbros were emplaced in the core of preexisting structures developed during the extensional stage and linked to basement faults. These structures were reactivated as anticlines during the Cenozoic compressional inversion. Gabbros from 19 out of the 33 sampled sites show a stable characteristic magnetization, carried by magnetite, which has been interpreted as a primary component. This component shows an important dispersion due to postemplacement tectonic movements. The absence of paleoposition markers in these igneous rocks precludes direct restorations. A novel approach analyzing the orientation of the primary magnetization is used here to restore the magmatic bodies and to understand the deformational history recorded by these rocks. Paleomagnetic vectors are distributed along small circles with horizontal axes, indicating horizontal axis rotations of the gabbro bodies. These rotations are higher when the ratio between shales and gabbros in the core of the anticlines increases. Due to the uncertainties inherent to this work (the igneous bodies recording strong rotations), interpretations must be qualitative. The magnetic fabric is carried by ferromagnetic (s.s.) minerals mimicking the magmatic fabric. Anisotropy of magnetic susceptibility (AMS) axes, using the rotation routine inferred from paleomagnetic results, result in more tightly clustered magnetic lineations, which also become horizontal and are considered in terms of magma flow trend during its emplacement: NW‐SE (parallel to the general extensional direction) in the western sector and NE‐SW (parallel to the main faults) in the easternmost structures. Key Points: A novel approach to restore paleomagnetic data from deformed igneous rocks is described New paleomagnetic and magnetic fabric data from Jurassic gabbros of NW Africa are provided This study allows a better and more complete constraint of the deformational history of the central High Atlas