PETROGRAPHIC AND ANISOTROPY OF MAGNETIC SUSCEPTIBILITY (AMS) STUDIES OF SOME IGNEOUS ROCKS AT ABU-SHIHAT AREA, NORTHERN EASTERN DESERT, EGYPT

Document Type : Original Article

Authors

1 (1) Nuclear Materials Authority, Cairo, Egypt.

2 (2) Menofiya University, Shebin Elkoam, Menofiya, Egypt.

Abstract

Abu-Shihat area is covered by basement rocks of Precambrian age. Petrographic studies revealed that the study area is represented by amphibolites, diorites, monzogranites and pegmatites. Laboratory measurements (magnetic susceptibility and anisotropy of magnetic susceptibility (AMS)) were conducted on 114 samples, gathered from the four rock types in order to describe the behaviour of magnetic susceptibility, determine the direction of magma flow and investigate the preferred orientation of the prevailing structures that affected the different rock units constituting the study area.
The magnetic susceptibilities of the amphibolites and monzogranites are due to magnetite and/or ilmenite, while for diorites and pegmatites are due to paramagnetic minerals. The magnetic fabrics of diorites and monzogranites are interpreted as being primary related to the original emplacement process through magma flow, with subsequent cooling and crystallization under relatively static conditions. The magnetic fabrics of the amphibolites and pegmatites were interpreted as being secondary, which were acquired during late tectonic stages after emplacement and cooling. The determined AMS directions for the four rock types revealed relatively well-defined poles of magnetic foliation (K3). The foliation planes for these rocks were shallow to moderate with directions parallel to their elongation trends in the study area.

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