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Emplacement and deformation of mesozoic Gabbros of the High Atlas (Morocco): paleomagnetism and magnetic fabrics

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Calvín Ballester, Pablo and Ruíz Martínez, Vicente Carlos and Villalaín Santamaría, Juan José and Casa Sainz, Antonio María and Moussaid, Bennacer (2017) Emplacement and deformation of mesozoic Gabbros of the High Atlas (Morocco): paleomagnetism and magnetic fabrics. Tectonics, 36 (12). pp. 3012-3037. ISSN 0278-7407

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Official URL: http://dx.doi.org/10.1002/2017TC004578


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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.


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©2017 American Geophysical Union
This study was financed by the research projects CGL2012-38481 and CGL2016-77560 of the MINECO (Spanish Ministry of Economy and Competitiveness) with also FEDER funding (European Union). P. C. also acknowledges the MINECO for the F.P.I. research grant BES-2013-062988. The authors acknowledge Abdelkader Mahmoudi and Hmidou El Ouardi for helping in field work and Carlos Rossi for carrying out the extracts of the silicate crystals. Institute for Rock Magnetism (University of Minnesota, USA) and specifically Mike Jackson are thanked for rock magnetic measurement support. The authors also acknowledge the constructive revisions, comments, and suggestion from Helga de Wall and three anonymous reviewers. Raw data are in the supporting information.

Uncontrolled Keywords:Modipe gabbro; Susceptibility anisotropy; Layered intrusion; Troodos ophiolite; Central Pyrenees; South-Africa; Shear zone; Axial zone; Granite; Pluton; Gabbro; Paleomagnetism; Magnetic fabric; High Atlas; Paleomagnetic restoration; Small circles
Subjects:Sciences > Physics > Geophysics
Sciences > Physics > Meteorology
ID Code:46817
Deposited On:12 Mar 2018 19:38
Last Modified:01 Jun 2018 23:01

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