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Cipriani, Anna
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- PublicationOpen AccessWater in Mid Ocean Ridge Basalts: Some Like it Hot, Some Like it Cold(Consiglio Nazionale delle Ricerche, 2011-11)
; ; ; ; ; ;Ligi, M.; Istituto di Scienze Marine - CNR ;Bonatti, E.; Lamont Doherty Earth Observatory - Columbia University, New York (USA) ;Brunelli, D.; Dipartimento Scienze della Terra, Università di Modena ;Cipriani, A.; Dipartimento Scienze della Terra, Università di Modena ;Ottolini, L.; Istituto di Geoscienze e Georisorse - CNR; ; ; ; ; ; ; ; ; ; ; ;Brugnoli, Enrico; DTA-CNR ;Cavarretta, Giuseppe; DTA-CNR ;Mazzola, Salvatore; IAMC-CNR ;Trincardi, Fabio; ISMAR-CNR ;Ravaioli, Mariangela; ISMAR-CNR ;Santoleri, Rosalia; CNR; ; ; ; ; The presence in the Earth’s mantle of even small amounts of water and other volatiles has major effects: first, it lowers drastically mantle’s viscosity, thereby facilitating convection and plate tectonics; second, it lowers the melting temperature of the rising mantle affecting the formation of the oceanic crust. H2O concentration in oceanic basalts stays below 0.2 wt% except for basalts sampled near “hot spots” that contain significantly more H2O than normal MORB, implying that their mantle plume sources are unusually H2O-rich. Basalts sampled in the Equatorial Atlantic close to the Romanche transform, a thermal minimum in the Ridge system, have a H2O content that increases as the ridge is cooled approaching the transform offset. These basalts are Na-rich, being generated by low degrees of melting of the mantle, and contain unusually high ratios of light versus heavy rare earth elements implying the presence of garnet in the melting region. H2O enrichment is due not to an unusually H2O-rich mantle source, but to a low extent of melting of the upwelling mantle, confined to a deep wet melting region. Numerical models predict that this wet melting process takes place mostly in the mantle zone of stability of garnet. This prediction is verified by the geochemistry of our basalts showing that garnet must indeed have been present in their mantle source. Thus, oceanic basalts are H2O-rich not only near “hot spots”, but also at “cold spots”.177 435 - 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 - PublicationRestrictedConstraining the onset of flexural subsidence and peripheral bulge extension in the Miocene foreland of the southern Apennines (Italy) by Sr-isotope stratigraphy(2020)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; In fold and thrust belts developing at convergent margins, the migration of the advancing wedge is accompanied by bulging of the downgoing plate, followed by the development of a foredeep basin filled by a thick succession of syn-orogenic sediments. The transition from forebulge to foredeep marks a key moment in the evolution of the orogenic system. In deep water environments, the record of this transition is typically complete and progressive. Conversely, in the shallow-water/continental environment of many collisional systems, the uplift of the forebulge area can imply emersion and erosion, obliterating the stratigraphic record of key steps of the evolution of the orogenic system. The southern Apennines constitute one of these collisional fold and thrust belts where the development of the forebulge has implied emersion and erosion, with the development of a Miocene forebulge erosional unconformity, accompanied by extensional deformation associated with the bending of the lithosphere during the forebulge stage. In this paper, we use strontium isotope stratigraphy to constrain with unprecedented time-resolution the age of the forebulge unconformity in areas presently incorporated in the northern sector of the southern Apennines fold and thrust belt. Integration of our results and those of previous studies indicates, at the regional scale, a younging toward the foreland of the forebulge unconformity across the belt. Our highresolution ages also reveal a diachronous onset of the flexural subsidence over short distances, associated with the occurrence of horst and graben structures, possibly resulting from inherited paleotopography along with forebulge extension. This work highlights how high-resolution dating is critical to unravel the evolution of foreland basin systems at different scales.417 3 - PublicationOpen AccessForebulge migration in the foreland basin system of the central‐southern Apennine fold‐thrust belt (Italy): New high‐resolution Sr‐isotope dating constraints(2021)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; The Apennines are a retreating collisional belt where the foreland basin system, across large domains, is floored by a subaerial forebulge unconformity developed due to forebulge uplift and erosion. This unconformity is overlain by a diachronous sequence of three lithostratigraphic units made of (a) shallow-water carbonates, (b) hemipelagic marls and shales and (c) siliciclastic turbidites. Typically, the latter two have been interpreted regionally as the onset of syn-orogenic deposition in the foredeep depozone, whereas little attention has been given to the underlying unit. Accordingly, the rate of migration of the central-southern Apennine fold-thrust beltforeland basin system has been constrained, so far, exclusively considering the age of the hemipelagites and turbidites, which largely post-date the onset of foredeep depozone. In this work, we provide new high-resolution ages obtained by strontium isotope stratigraphy applied to calcitic bivalve shells sampled at the base of the first syn-orogenic deposits overlying the Eocene-Cretaceous pre-orogenic substratum. Integration of our results with published data indicates progressive rejuvenation of the strata sealing the forebulge unconformity towards the outer portions of the foldthrust belt. In particular, the age of the forebulge unconformity linearly scales with the pre-orogenic position of the analysed sites, pointing to an overall constant migration velocity of the forebulge wave in the last 25 Myr.372 15 - 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 - PublicationOpen AccessSea-floor spreading initiation: constraints from geophysical data of the Thetis Deep, northern Red Sea(2008-12-15)
; ; ; ; ; ; ; ; ; ;Ligi, M.; CNR-ISMAR Bologna ;Bonatti, E.; CNR-ISMAR Bologna ;Bortoluzzi, G.; CNR-ISMAR Bologna ;Brunelli, D.; Università di Modena, Dipartimento di Scienze della Terra ;Caratori Tontini, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Cipriani, A.; Doherty Earth Observatory, Columbia University, ;Cocchi, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Cuffaro, M.; CNR-ISMAR Bologna ;Ferrante, V.; CNR-ISMAR Bologna; ; ; ; ;; ; ; A major step in the "Wilson Cycle" is the splitting of a continent and the birth of a new ocean, with the consequent formation of passive plate margins. The transition from a continental to an oceanic rift can be observed today nowhere better than in the Red Sea/Gulf of Aden system. We have carried out during several years a number of expeditions in the axial portion of the Northern Red Sea, in the region where the northernmost nuclei of axial emplacement of oceanic crust can be observed. High resolution multibeam, magnetics, gravity and multichannel seismic reflection surveys from the Thetis Deep revealed rates and modes of initial pulses of sea floor spreading, velocity of S to N axial propagation of the oceanic rift, evolution of initial MORB-type crust and nature of the mantle thermal anomaly that caused the transition from a continental to an oceanic rift. The Thetis deep is made of three en echelon fault-bounded axial basins that are joined together with axial volcanic ridges and a large number of scattered small central volcanoes. The southern basin shows a strong linear magnetic anomaly corresponding to the axial neo-volcanic zone. Two negative symmetric anomalies identified as Matuyama are present in the southernmost part of this basin, suggesting that the emplacement of oceanic crust at this site started roughly 2.5 Ma, with an average half spreading rate of 6 mm/yr. The central sub-basin is also characterized by a strongly magnetic linear neo- volcanic zone that, however, is flanked only by a small, "vanishing" symmetrical negative anomaly suggesting emplacement of oceanic crust not earlier than about 1 Ma. The northern sub-basin does not show a clearly defined linear neo-volcanic zone although it displays a strong central magnetization suggesting initial emplacement of oceanic crust < 0.7 Ma. This pattern implies a south to north time progression of the initial emplacement of oceanic crust within the Thetis system, with a propagation rate of about 20 mm/yr. Gravity data inversions constrained by seismic data reveal that the oceanic crust extends from the axial neo-volcanic ridges toward the master faults of the axial depression with crustal thickness ranging from 4 to 6 km. The increasing thickness of basaltic crust toward the edges of the basin together with higher degree of melting, inferred by the geochemistry of the basaltic glasses, and higher central magnetization of the northernmost and youngest basin suggest a pulse of faster spreading rate at the onset of sea-floor spreading.269 88