| Magmatic and Structural Interactions during the Emplacement of a Neoproterozoic Gabbro–Tonalite–Granodiorite Complex, Atud Area, Eastern Desert, Egypt |
| Paper ID : 1074-ISCH |
| Authors |
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Sayed M. Sayed *1, Reda Abdu Yousef El-Qassas2, Mohamed H. M. Yousef3, Amin Esmail Khalil1, Yahia A. El Kazzaz1 1Department of Geology, Faculty of Science, Helwan University, P.O. 11795, Cairo, Egypt 2Ground Geophysics Department, Exploration Sector, Nuclear Materials Authority (NMA), P.O. Box 530, Maadi, Cairo, Egypt 3Nuclear Materials Authority, P.O. Box, 530, Maadi, Cairo, Egypt |
| Abstract |
| The mechanisms of magma emplacement in active orogenic belts remain a fundamental topic in Earth sciences. The Neoproterozoic Gabbro-Tonalite-Granodiorite Complex, Atud Area, located in the Eastern desert of Egypt, presents a series of geological paradoxes that challenge simple intrusion models. Field relationships reveal seemingly contradictory evidence, including: a contact between granodiorite and underlying tonalite that is simultaneously mylonitic and gradational; and bodies of gabbro that are structurally thrusted over the granodiorite, while also existing as older xenoliths within it. This study integrates field mapping, petrography, aeromagnetic data, and Anisotropy of Magnetic Susceptibility (AMS) measurements to resolve these paradoxes. Aeromagnetic data reveal a deep-seated E-W structural grain, interpreted as the primary crustal weakness that localized the shear system and controlled initial magma ascent. We propose a dynamic, four-stage, time-transgressive emplacement model that occurred within a continuously active, crustal-scale compressional shear zone. The model begins with the syn-tectonic sheet intrusion of tonalite, which established a rigid rheological floor. This was followed by the intrusion of an early gabbro, which was subsequently stoped as xenoliths by the main-phase, incrementally emplaced granodiorite. The granodiorite magma chamber evolved as a long-lived system, allowing for simultaneous mylonitization at its solidifying base and magma mingling in its mushy interior. Finally, after the entire complex solidified, continued regional compression resulted in late-stage, intra-pluton thrusting, which placed slices of the older, more rigid gabbro over the younger granodiorite. AMS data quantitatively support this model, revealing distinct magmatic and solid-state tectonic fabrics corresponding to specific emplacement stages. |
| Keywords |
| Syn-tectonic magmatism, Pluton emplacement, Arabian-Nubian Shield, Shear zone, Aeromagnetics, Anisotropy of Magnetic Susceptibility (AMS) |
| Status: Abstract Accepted (Poster Presentation) |