Geological studies and structural analysis of the Umm Anab metavolcanics and related quartz veins: implications for Pan-African volcanism in the Egyptian Nubian Shield

Abstract

HE NEOPROTEROZOIC basement complex of the Umm Anab area is located 40 km southwest of Hurghada city in the Northern Eastern Desert (NED) of Egypt. The basement rocks include metavolcanics and enormous plutons of granitoid rocks. The metavolcanics are regionally metamorphosed, forming greenschist to amphibolite facies rocks interbedded with banded iron formation (BIF). Structural analysis in the Umm Anab metavolcanics (UAV) indicates that the area has a poly-phase structural deformation, and each phase has its own effect and style. A Well-developed schistosity striking approximately E-W with dipping 60º-80º southward, and asymmetrical folds with oblique subvertical NNW-striking axial planes were observed. The structural analysis of the veins in metavolcanic by using GArcmB software determined the paleostress inversion and displayed two clusters of veins that formed under two stresses. The stress ratios ( Φ )= ( σ 2 – σ 3) / ( σ 1 – σ 3) for both clusters, respectively, are ~0.39 and ~0.16, which shows two stress status. The values of the stress ratio on vein walls suggest that the host rock was subject to low to moderate tectonic stress at the time the veins formation. In addition, finite strain results in metavolcanics were estimated using the Rf/φ method on deformed pebbles (with a trend of N73º-88ºE), confirming the idea that metavolcanics are affected by low to moderate deformation. The stretching mineral lineation and BIF have trend ENE-WSW to E-W that supports the oldest shortening event (D1) which is considered an early phase of deformation NNW–SSE linked with the Pan-African thrusting.