Geophysical and Geochemical Signature of Rare Metal Granites, Central Eastern Desert, Egypt: Implications for Tectonic Environment

Abstract

Magnetic survey is usually used to delineate magnetic-structural lineaments, analyze their relationships to the inherited ductile fabrics and estimate the depth of perturbing body sources, probably granitic intrusions. These were conducted on the total magnetic intensity reduced to the pole map as well as First vertical derivative and Euler deconvolution maps to show various aeromagnetic structural lineaments which were interpreted as fault systems on the interpretation maps. The early deformational event (D1) produced sets of NE-SW striking local and regional fractures and faults. The second deformational event (D2) generated mainly NNW-SSE and NW-SE faults and fractures some of which intersected earlier (D1) structures. At the northern and eastern parts of the study area (D1/D2) intersections are observed. The last event (D3)created NNE-SSW set of fractures and faults brought out by splay of dykes and reactivated some (D1 and D2)fractures and faults. The study area is also characterized by a major, N-S trending, late-stage dyke system that extend through the area. In order to estimate source depths from gridded aeromagnetic data, 3-D Euler deconvolution method was applied. The calculated source depths are in the range of 200 m to 3500 m. The deepest structures are in the ENE-WSW direction and have depths ranging from about 1100 m to 3000 m in the southeastern part of the study area. On the other hand, the network of parallel major structures trending in NNW-SSE direction have a shallow depth of about 700 m. Rare-metal granites of the Central Eastern Desert of Egypt are classified chemically into alkaline to peralkaline and peraluminous granites. They display the typical geochemical characteristics of A-type granites, with high SiO₂, Na₂O+K₂O, Rb, Zr, Nb, Ta, Sn, and Y, and low CaO, MgO, Ba and Sr. The magmatism of the rare metal granites of the Central Eastern Desert are related to anorogenic, within-plate, A-type, subvolcanic setting and emplaced in the extensional tectonic regime along to the inherited ductile fabrics.