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Dense mantle flows periodically spaced below ocean basins / Isabelle Panet in Earth and planetary science letters, vol 594 (15 September 2022)  

Public [article]  inEarth and planetary science letters > vol 594 (15 September 2022) . - n° 117745 Titre : Dense mantle flows periodically spaced below ocean basins Type de document : Article/Communication Auteurs : Isabelle Panet , Auteur ; Marianne Greff-Lefftz, Auteur ; Barbara Romanowicz, Auteur Année de publication : 2022 Projets : Université de Paris / Clerici, Christine Article en page(s) : n° 117745 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] champ de pesanteur terrestre [Termes IGN] convection [Termes IGN] déformation de la croute terrestre [Termes IGN] dynamique des fluides [Termes IGN] fond marin [Termes IGN] Indien (océan) [Termes IGN] lithosphère [Termes IGN] manteau terrestre [Termes IGN] Pacifique (océan) Résumé : (auteur) Understanding mantle flow is key to elucidate how deep Earth dynamics relate to tectonics at the global scale. The convective mass transport is reflected in lateral variations of the gravity field, seismic velocities, as well as deformations of the Earth's surface. Yet, upper to mid-mantle dynamics have been difficult to constrain at the medium scales of thousands of km. Here, we analyze the second-order horizontal derivatives of seafloor topography and of the gravity potential over the Pacific and Northern Indian ocean basins, and provide evidence for periodic undulations of 1600-2000 km wavelength in both signals, elongated along the direction of absolute plate motion. We investigate potential crustal and lithospheric sources and show that at least part of this signal must originate below the lithosphere, with alignments of sub-lithospheric upper mantle mass excess below seafloor lows. Furthermore, we find that these alignments coincide geographically over wide areas with similarly periodic slow seismic velocity fingers located at upper mantle depths. These two fields may thus record an intermediate scale of mantle convection below ocean basins, which cannot be explained by purely thermal convection and requires instead lateral variations in composition in the upper mantle. Elucidating the nature of the detected mass excess sources coincident with the slow seismic velocities calls for a joint dynamical modeling of all observations in a thermo-chemical context. Numéro de notice : A2022-692 Affiliation des auteurs : UMR IPGP-Géod+Ext (2020- ) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.epsl.2022.117745 En ligne : https://doi.org/10.1016/j.epsl.2022.117745 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=101809 [article]

Reconciling upper mantle seismic velocity and density structure below ocean basins / Isabelle Panet (2019)

Public Titre : Reconciling upper mantle seismic velocity and density structure below ocean basins Type de document : Article/Communication Auteurs : Isabelle Panet , Auteur ; Barbara Romanowicz, Auteur ; Marianne Greff-Lefftz, Auteur Editeur : Saint-Mandé : Institut national de l'information géographique et forestière - IGN (2012-) Année de publication : 2019 Projets : 1-Pas de projet / Clerici, Christine Conférence : AGU 2019 Fall Meeting 09/12/2019 13/12/2019 San Francisco Californie - Etats-Unis programme sans actes Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] champ de pesanteur terrestre [Termes IGN] déformation de la croute terrestre [Termes IGN] données bathymétriques [Termes IGN] données GRACE [Termes IGN] fond marin [Termes IGN] geoïde marin [Termes IGN] géophysique interne [Termes IGN] Indien (océan) [Termes IGN] manteau terrestre [Termes IGN] Pacifique (océan) [Termes IGN] structure géologique [Termes IGN] vitesse de déplacement Résumé : (auteur) Imaging the spatial pattern of mantle flows and constraining their mass is one of the keys to understand the character of mantle convection inside the Earth, and its interactions with plate motions. The horizontal planform of the flows, their heterogeneity and mass transport at depth, are reflected in variations of the gravity field and seismic velocities, as well as deformations of the Earth's surface. Over ocean basins, these observables show an elusive medium-scale structure. A 1500-2000 km wavelength directional fabric following the present-day absolute plate motion is present in the Pacific Ocean in GRACE satellite gravity data (Hayn et al., 2012), while 2000-km wavelength slow shear velocity anomalies sharing a similar orientation are found in seismic tomography at upper mantle depths below the oceans (SEMUM2, French et al., 2013). Today, the dynamic processes at the origin of these observations remain unresolved. Here, we develop a joint analysis of satellite gravity and bathymetry data together with the SEMUM2 seismic tomography model, in order to advance our understanding of upper to mid-mantle flows below the oceans. First, we enhance and reconstruct the medium-scale gravity and seafloor topography signals aligned with the present-day plate motion from an analysis of the rates of gravity vector variations and seafloor slopes. Then, we compare the obtained signals with the spatial distribution of shear velocity anomalies at depth. We show that slow velocity anomalies coincide with geoid lows, depressions in the seafloor topography, and mass excess in the mantle, in the Pacific ocean and part of the Indian ocean. We first consider a purely thermal interpretation of the seismic velocity variations, associated with medium-scale convective rolls in the upper to mid-mantle, a process able to only explain the observed geometry of anomalies. Investigating whether the needed mass excess arises from lithospheric or deeper sources, such as at the level of the 660-km interface, we conclude that it lies more likely within the slow velocity anomalies themselves, suggesting hot and dense structures. We finally discuss the possible meaning and implications of these results. Numéro de notice : C2019-058 Affiliation des auteurs : Géodésie+Ext (mi2018-2019) Thématique : POSITIONNEMENT Nature : Poster nature-HAL : Poster-avec-CL DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=96896