Paleoproterozoic structural evolution of the Eglab domain (Eglab shield, Algeria) from aeromagnetic data and anisotropy of magnetic susceptibility (AMS) study of the post-collisional Aftout granitoids

摘要

New interpretation of the aeromagnetic data allowed strong improvement in the knowledge of the Eglab domain, better specifying major deep structures. This domain corresponds to a regional extension of the unfoliated Aftout granitoids. In order to correlate this deep structures with those at the rock scale, AMS analyses were performed on these Aftout granitoids. Samples were collected in spaced sites along long profiles. Rockmagnetic studies have shown that magnetic fabric is mainly carried by large magnetite grains. AMS data appeared with different characteristics within two large compartments separated by a NE-SW limit that corresponds to a border of the Kahal Morrat corridor (KMC), a major structure evidenced by aeromagnetic data analyses. To the SE, the magnetic foliation and lineation are homogeneous (mainly ESE-WNW to E-W subvertical magnetic foliation and subhorizontal magnetic lineation). To the NW, the declination of the magnetic foliation and the plunge of the magnetic lineation show significant local variations, without coherency from one site to another. That highlights different stress field conditions (and then different depths) during emplacement. The major deep crustal structure separating these two compartments allowed a considerable relative uplift of the SE part of the Eglab domain relatively to the NW part. This period was also characterized by a cataclysmic volcanism in a very large area around the KMC, suggesting a relation with this deep structure.