Northern Red Sea: Nucleation of an oceanic spreading center within a continental rift

Abstract

[1] The northern Red Sea is an amagmatic continental rift in which an oceanic spreading center is beginning to develop. A new compilation of marine geophysical data permits delineation of the structure of the northern Red Sea and of the manner in which the transition from continental to oceanic extension is occurring in this rift. The margins of the northern Red Sea are formed by large, apparently active faults on the seaward edge of the narrow continental shelves. The morphology of the main trough is a series of terraces stepping down to an axial depression. The terraces are a subdued expression of the basement structure, which consists of a series of large rotated fault blocks. The axial depression is an often faultbounded axis of deep water that extends south from the Suez triple junction. The rift is segmented alongstrike by throughgoing accommodation zones spaced at 40-60 km intervals along the rift. In the main trough, accommodation zones truncate or offset rift-parallel bathymetric and gravity features. The axial depression consists of a series of discrete depressions offset from each other and separated by slightly shallower areas corresponding to accommodation zones. Within each segment, the axial depression deepens away from the accommodation zones toward a small deep, a few kilometers across and a few hundred meters deeper than the surrounding seafloor. A pair of small volcanoes is perched on top of the scarps bounding the axial depression on either side of the deep within each segment. The volcanoes are all normally magnetized and interpreted as very young. The crust is uniformly thin (5-8.5 km) throughout the main trough, implying extension evenly spread across the rift through much of its development. As extension recently became concentrated at the axis, melt began to be generated and is focused to a location within the segment where it ascends along faults bounding the axial depression to form the pair of volcanoes flanking the axis. A volcano is also found on the floor of the axial depression in one segment. This isolated volcano appears to be the first step in the development of the seafloor spreading cells that are observed in the central Red Sea. The individual cells then grow and coalesce to become a continuous spreading axis.Components: 17,282 words, 24 figures.

Seismic structure beneath the Gulf of Aqaba and adjacent areas based on the tomographic inversion of regional earthquake data

“…However, more recent studies (Cochran, 2005;Cochran and Karner, 2007) report clear axial depression of the bathymetry and aligned magnetic anomalies as well as a chain of dykes that are more typical for rifting processes. In our study, we can see that the high-velocity anomaly in the Red Sea has very sharp bounds coinciding with the coastline; this presumes an abrupt difference in crustal properties between the onshore and offshore areas at all depth intervals.…”

Architecture of rifted continental margins and break-up evolution: insights from the South Atlantic, North Atlantic and Red Sea–Gulf of Aden conjugate margins

“…Dredging samples and side-scan images indicate that the spreading center is associated with volcanic features, basaltic rocks and gabbros (Monin et al 1982;Cochran 1983;Cochran 2005;Cochran & Karner 2007, Mitchell et al 2010. Some of the recent presalt exploratory boreholes in the South Atlantic, drilled in regions close the continent-ocean edge, have also penetrated basalts and gabbros (Mohriak, 2011).…”

The major tectonic boundaries of the Northern Red Sea rift, Egypt derived from geophysical data analysis

“…The floor of the Gulf of Suez is quite smooth and the depth of water is shallow, averaging about 55 m. In contrast, the Gulf of Aqaba has varied bottom topography with much greater depths of water reaching 1460 m. The bathymetry of the active, main trough of the northern Red Sea rift, consists of a series of terraces stepping down to an axial depression at a depth of 1100-1200 m (Martinez and Cochran, 1988;Cochran, 2005). Sediment deformation within the axial depression is much more intense than in the remainder of the Red Sea (Knott et al, 1966;Guennoc et al, 1988;Martinez and Cochran, 1988), implying that tectonic activity and extension is presently concentrated predominantly in the axial depression.…”

“…Based on the geophysical data in the Northern Red Sea, Cochran (2005) suggested that rift development occurs via the rotation of large crustal fault blocks that sole into a zone of plastic creep in the lower crust, resulting in a flat Moho and high upper crustal relief. Initial broadly distributed extension is eventually replaced by focused extension at the rift axis leading to rapid lithospheric thinning and melt generation.…”

“…Initial broadly distributed extension is eventually replaced by focused extension at the rift axis leading to rapid lithospheric thinning and melt generation. Melt formed within individual rift segments is focused to form small axial volcanoes (Cochran 2005).…”