Tectonic evolution of oceans from initiation to drifting: example from the Red Sea

Abstract

The Red Sea Rift which separates the African continent from the Arabian continent is an example of a young oceanic basin on the modern Earth. Understanding the architecture and evolution of this unusually preserved tectonic environment allow critique of the transition between continental rifting and ocean spreading that may not be immediately apparent from relatively sparse data in ancient examples, and enable assessment of the tectonic drivers of ocean basin formation. This thesis presents an integrated study of field investigation from the Farasan Islands, remote sensing data and interpretation and modeling of regional geophysical datasets throughout the Red Sea. Field work investigation of the Farasan Islands indicated that the stratigraphic succession that form part of the Farasan Bank. The outcrop of the Farasan Islands consists of a Miocene shale unit, overlain by Pliocene marly limestone unit, overlain inturn by reefal limestone unit. In the subsurface, a thick evaporate succession up to 4 km underlies the Farasan Bank. The evaporate succession comprises eight prominent salt domes in the Farasan bank based on the modeling of the observed gravity gradient constrained by wells data. Salt diapirs sourced from Miocene evaporites have resulted in Salt doming with elongate geometries parallel or orthogonal to the axis of the Red Sea rift axis, suggesting diapirism was influenced by existing basement structures The Farasan limestone’s have been deformed by salt diapirsm into a varies of mapped structures including normal faults, salt domes, anticlinal salt ridges solution holes and collapse breccia. The islands show evidence of resent extensional faults away from the mid ocean ridge, suggesting that separation between the Arabian and African plates is not taken up by extension along the mid ocean ridge alone. Gravity data were collected during field work in Ras Hasis and Kilah area to obtain high resolution data. The structure observations during filed work is supported by the gravity data as it show that these areas features are presented by low gravity anomaly and largely controlled by extensional tectonics. These have a prevailing NW-SE orientation that is parallel to the present day coast, the orientation of the islands and the current mid oceanic ridge. The data also confirm that the islands are strongly faulted as a result of salt diapirism, many of the faults being parallel to the rift axis in NW-SE. An integrated synthesis of aeromagnetic, gravity and seismic refraction data along the Arabian shelf (Farasan Bank) and part of the Arabian Shield at southern Red Sea show remarkable complexity for the opening of the Red Sea, including multiple episodes of spreading, several failed attempts of rifting along the Arabian Escarpment, and ongoing crustal extension on the flanks of the mid ocean ridge as salt tectonics taken control in the modern environment, which have not been documented or interpreted in the past. Seven magnetic stripes identified in aeromagnetic data using different processing techniques. Modeling of the potential-field datasets illustrate that the Farasan Bank is likely to be floored by oceanic and transition crust based on the magnetic anomalies wavelength characteristic and behavior and density variation, which calls into question the concept that the Arabian Shelf represents a passive margin. The model illustrates the effectiveness of integrating potential field data for tectonic analysis of modern systems. Modelling of global potential field datasets shows that the architecture of the Red Sea is more complex with a resent spreading restricted to the southern and central sectors whereas the northern and southernmost Red Sea are still floored by thinned continental crust. These models marked variations in the crustal structure along the entire length of the Red Sea. The architecture suggests that ocean basin initiation occurs initially as a series of cells or windows surrounded by transitional crust along the strike of the Red Sea. These observations suggest that the Red Sea is not linked with the Gulf of Aden and the global rift network, nor does the observation support tectonic models that suggest oceans unzip or that the Afar plume is a primary control for the initiation of the Red Sea.