Abstract
The role of magmatism in continental rupture at the birth of a new ocean is poorly understood. Continental rupture can take place with voluminous volcanism, as in the southern Red Sea, or in a relatively non-volcanic mode, as in the northern Red Sea. We report geophysical, geochemical and geochronological evidence suggesting that continental rupture in the northern Red Sea is preceded by MORB-type basaltic melt intrusions that cooled at depth forming gabbros at progressively shallower crustal levels as rifting progressed towards continental separation. One of these gabbros yielded an 40Ar/39Ar age of 25±6Ma, suggesting intrusion during early rifting. A magma chamber we detected 3.5km below Thetis Deep, an axial segment of initial oceanic crust accretion, represents the final stage in this progression. Oceanic crust accretion in the Red Sea rift starts first at depth before continental rupture and initiation of sea floor spreading.
Highlights
IntroductionAs hinted already by Alfred Wegener over 80 years ago (Wegener, 1929), the Red Sea provides today the prime example of a rupturing continent, with Arabia separating from Africa, and a new ocean being born in between
We present here 3D seismic reflection and gravity data obtained from an off-axis area of the NW Red Sea (Fig. 1), as well as a study of gabbroic rocks recovered in the same area both from an oil well (QUSEIR B-1X) below a thick syn-rift sediment pile, and from a layered mafic complex exposed on the Brothers islands (Fig. 2)
This implies that the Brothers and QUSEIR gabbros were intruded into sub-rift continental crust and exhumed by footwall-uplift during extension and block rotation, in a mechanism similar to that proposed for the basement cores of oceanic core complexes and/or of fault blocks exposed in the Gulf of Suez (Bosworth et al, 2005)
Summary
As hinted already by Alfred Wegener over 80 years ago (Wegener, 1929), the Red Sea provides today the prime example of a rupturing continent, with Arabia separating from Africa, and a new ocean being born in between. We present here 3D seismic reflection and gravity data obtained from an off-axis area of the NW Red Sea (Fig. 1), as well as a study of gabbroic rocks recovered in the same area both from an oil well (QUSEIR B-1X) below a thick syn-rift sediment pile, and from a layered mafic complex exposed on the Brothers islands (Fig. 2) These gabbros show geochemical signatures similar to those of mid-ocean ridge basalts (MORB) (Fig. 3). We detected a magma chamber beneath Thetis Deep, an axial cell of initial oceanic crust formation (Fig. 4) These new data suggest progressively shallower intrusions of MORB-type melts during rifting, implying that “oceanization” in the northern Red Sea occurred first at depth, preceding continental rupture and sea floor spreading
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