Geometry and growth of syn-tectonic plutons emplaced in thrust shear zones: Insights from Abu Ziran pluton, Egypt

Coupling of deformation and magmatism has been widely reported in several old orogenic belts, particularly along faults and shear zones. The syn-kinematic plutons in exhumed shear zones offer the best opportunity to understand the complex relationship between magmatism and regional deformation. The present paper investigates the geometry and internal structure of granite plutons emplaced in thrust faults and shear zones, and structural control on their emplacement mechanism. Abu Ziran pluton is an example of the intrusions emplaced in an active brittle-ductile thrust shear zone in the Nubian shield, and documents clear evidence on the interaction between magmatism and deformation during melt ascent and emplacement. Results from detailed geological mapping, remote sensing and structural analysis of the pluton permitted the constraining of the pluton's geometry, emplacement mechanism, and spatio-temporal evolution. Structural analysis indicates that pluton emplacement was syn-to-late-tectonic. The brittle-ductile fabrics in the wall rock are consistent with a sub-horizontal thrust shear zone with a top-to-NW shear sense. The activity of the shear zone was accompanied by an episode of a calc-alkaline magmatic pulse. Granitic magma ascended upward via non-exposed feeder dykes, or through ramps and flats in the thrust system and emplaced laterally along the shear zone, forming complex sub-horizontal sheet-shaped intrusion. The geometry and extent of pluton emphasize that inherited heterogeneities and regional stress states played important role in the emplacement processes. In addition, localization of pluton along or near the contact between ophiolitic nappes and mylonitic metasediments suggests that the rheological boundaries act as barriers that impede the rise of ascending magma, causing magma arrest and trigger lateral spreading and emplacement. The outcomes of this study allowed the reconstruction of the geometry and internal structure of Abu Ziran pluton and grasping its evolution in space and time. •Exhumed thrust shear zones documents a coupling of magmatic and deformational processes.•Plutons emplaced in shear zones have a distinctive tabular or sheet-shaped geometry.•Inherited structures and stress states play a significant control on the room required for magma emplacement.•Rheological boundaries in the orogenic belts act as a trap for ascending melt.•Syn-kinematic plutons record a spectrum of microstructures ranging from magmatic to solid-state fab