Syn- and post-accretionary structures in the Neoproterozoic Central Allaqi-Heiani suture zone, Southeastern Egypt

Abstract

The Allaqi-Heiani suture (AHS) is the western part of the main Allaqi-Heiani-Gerf-Onib-Sol Hamed-Yanbu suture and represents one of the Neoproterozoic, arc–arc sutures in the Arabian-Nubian Shield (ANS). It separates the ca. 750Ma South Eastern Desert terrane in the north from the ca. 830–720Ma Gabgaba terrane in the south. The AHS is a deformed belt of ophiolitic rocks, syn-tectonic granitoids and metasediments. The central AHS zone is divided into three structural domains. The western domain (I) is characterized by NNE dipping thrusts and SSW-vergent folds. The central domain (II) includes upright tight to isoclinal NNW–SSE oriented folds and transpressional faults. The eastern domain (III) shows NNW–SSE oriented open folds. Structural analysis indicates that the area has a poly-phase deformation history involving at least two events. Event D1 was an N–S to NNE–SSW regional shortening generating the SSW-verging folds and the NNE dipping thrusts. Event D2 was an ENE–WSW shortening producing NNW–SSE oriented folds in the central and eastern parts of the study area and reactivating older thrusts with oblique-slip reverse fault movement. The tectonic evolution of the area involves two episodes of collision: an early collision between the South Eastern Desert terrane and the Gabgaba terrane along the AHS after the consumption of a basin floored by oceanic crust above a north-dipping subduction zone; and a later collision between East- and West-Gondwanas at ca. 750–650Ma, leading to the closure of the Mozambique Ocean. This collision deformed the AHS along N–S trending shortening zones and produced NW–SE and NE–SW oriented sinistral and dextral transpressional faults, respectively. The early collision episode is related to the terrane accretion during the early Pan-African orogen, while the later phase is related to a late Pan-African or Najd orogen.