Volume 20 N°2
2009
Abstrait
The Aïn Kahla granites are located along the N-S-trending Late Pan-African Arak major fouit, which separates the Ahnet and Mouydir basins (Algerian Saharan platform, North-West Hoggar). They belong to a crystalline and phyllo-crystalline complex located between a northem segment of the Arak fault in the West (Aïn Kahla fault) and one of its satellite faults at the East (called here «Eastern fault»). We analyze in this work the evolution of the anisotropy ofmagnetic susceptibility (AMS) ofthese granites over four sampling sites (with a total of 26 core samples) on an E-W cross section. The main magnetic carrier is magnetite, with multi-domain grained size. The shape parameter evolves from east to west, from a prolate shape to an oblate shape.
The mean magnetic foliation dips with a relatively low angle towards the west. It contains a W to WNW shallowly-dipping magnetic lineation. The main directions of the magnetic fabric cannot be correlated with those of the visible brittle structures (mainly regional cleavages S l and S2), that affected the granites at solid state later, likely at the end of the Paleozoic. lt would rather express structures related to the deformation acquired during magmatic to late-magmatic state of the granite, between the Pan-African and Early Paleozoic times, within a WNW-ESE to E-W regional stress field.
Mots clés : Mehdi Amine GUEMACHE, Bernard HENRY, Hamou DJELLIT and Mohamed El Messaoud DERDER