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Schettino, A.
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Schettino, A.
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- PublicationOpen AccessBirth of an ocean in the Red Sea: Initial pangs(2012-08-18)
; ; ; ; ; ; ; ; ; ;Ligi, M.; CNR-ISMAR Bologna ;Bonatti, E.; CNR-ISMAR Bologna ;Bortoluzzi, G.; CNR-ISMAR Bologna ;Cipriani, A.; CNR-ISMAR Bologna ;Cocchi, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Caratori Tontini, F.; GNS Science ;Carminati, E.; Università di Roma "La Sapienza" ;Ottolini, L.; CNR -Pavia ;Schettino, A.; Università di Camerino; ; ; ; ; ;; ; We obtained areal variations of crustal thickness, magnetic intensity, and degree of melting of the sub- axial upwelling mantle at Thetis and Nereus Deeps, the two northernmost axial segments of initial oceanic crustal accretion in the Red Sea, where Arabia is separating from Africa. The initial emplacement of oceanic crust occurred at South Thetis and Central Nereus roughly $2.2 and $2 Ma, respectively, and is taking place today in the northern Thetis and southern Nereus tips. Basaltic glasses major and trace element com- position suggests a rift-to-drift transition marked by magmatic activity with typical MORB signature, with no contamination by continental lithosphere, but with slight differences in mantle source composition and/or potential temperature between Thetis and Nereus. Eruption rate, spreading rate, magnetic intensity, crustal thickness and degree of mantle melting were highest at both Thetis and Nereus in the very initial phases of oceanic crust accretion, immediately after continental breakup, probably due to fast mantle upwelling enhanced by an initially strong horizontal thermal gradient. This is consistent with a rift model where the lower continental lithosphere has been replaced by upwelling asthenosphere before continental rupturing, implying depth-dependent extension due to decoupling between the upper and lower lithosphere with man- tle-lithosphere-necking breakup before crustal-necking breakup. Independent along-axis centers of upwell- ing form at the rifting stage just before oceanic crust accretion, with buoyancy-driven convection within a hot, low viscosity asthenosphere. Each initial axial cell taps a different asthenospheric source and serves as nucleus for axial propagation of oceanic accretion, resulting in linear segments of spreading.623 2204 - PublicationRestrictedInitial burst of oceanic crust accretion in the Red Sea due to edge driven mantle convection(2011-10-04)
; ; ; ; ; ; ; ; ; ; ; ;Ligi, M.; Istituto di Scienze Marine, Consiglio Nazionale delle Ricerche, Bologna ;Bonatti, E.; Istituto di Scienze Marine, Consiglio Nazionale delle Ricerche, Bologna e Lamont Doherty Earth Observatory, Columbia University ;Caratori Tontini, F.; GNS Science, Ocean Exploaration Section, New Zealand ;Cipriani, A.; Lamont Doherty Earth Observatory, Columbia University ;Cocchi, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Schettino, A.; Dipartimento di Scienze della Terra, Università di Camerino ;Bortoluzzi, G.; Istituto di Scienze Marine, Consiglio Nazionale delle Ricerche, Bologna ;Ferrante, V.; Istituto di Scienze Marine, Consiglio Nazionale delle Ricerche, Bologna ;Khalil, S.; Department of Geological and Biological Sciences, Suez Canal University, Egypt ;Mitchell, N.; School of Earth, Atmosphere and Environmental Sciences, University of Manchester ;Rasul, N.; Saudi Geological Survey, Saudi Arabia; ; ;; ; ; ; ; ; ; The 500 m.y. cycle whereby continents assemble in a single supercontinent and then fragment and disperse again involves the rupturing of a continent and the birth of a new ocean, with the formation of passive plate margins. This process is well displayed today in the Red Sea, where Arabia is separating from Africa. We carried out geophysical surveys and bottom rock sampling in the two Red Sea northernmost axial segments of initial oceanic crust accretion, Thetis and Nereus. Areal variations of crustal thickness, magnetic intensity, and degree of melting of the subaxial upwelling mantle reveal an initial burst of active oceanic crust generation and rapid seafloor spreading below each cell, occurring as soon as the lid of continental lithosphere breaks. This initial pulse may be caused by edge-driven subrift mantle convection, triggered by a strong horizontal thermal gradient between the cold continental lithosphere and the hot ascending asthenosphere. The thermal gradient weakens as the oceanic rift widens; therefore the initial active pulse fades into steady, more passive crustal accretion, with slower spreading and along axis rift propagation.544 91