Role of Pre-existing Structures During the Opening of the Red Sea, Western Saudi Arabian Margin

Abstract

Reactivation of continental basement structures during rifting can control fault patterns and basin architecture. Recent studies have shown that the obliquity of pre-existing anisotropies is critical to the style of overprinting. Here we investigated the role of a major Precambrian terrane boundary in controlling Cenozoic age Red Sea (RS) rifting: The Ad-Damn Shear Zone (ADSZ), western Saudi Arabian margin, separating the lowlands of the Jeddah terrane to the NW, from Asir terrane highlands to the SE. Regional lineaments analysis coupled with field observations reveals three major trends of Cenozoic fault- and dyke-sets that strike (i) RS-parallel (NW–SE), (ii) RS-oblique (N-S ±10°), and (iii) RS-normal (NE–SW), that record extension (i) E–W (ii) NW–SE, (ii) and (iii) NE–SW, respectively. Cenozoic structures (dykes and faults) are largely parallel to Precambrian foliations, resulting in abrupt changes in the dominant orientation of rift structures across the ADSZ. Measured fault kinematics and dyke opening directions show that structural reorientation also corresponds to abrupt changes in the principal strain axes. Within the ADSZ and Asir terranes, the extension is dominantly orthogonal to the main Red Sea rift, suggesting that the pre-existing structure has acted as a primary control on rift evolution.