58 research outputs found
Occurrence of high-Al N-MORB along the Easternmost Southwest Indian Ridge
No full textOne of the deepest and slowest part of the mid-ocean-ridge system lies within the easternmost part of the Southwest Indian Ridge between 61°E and 69° E. In this region, a distinctive sea-floor terrain characterized by high-relief segments separated by long, deep tectonized sections shows a predominance of tectonic over magmatic extensional processes, suggesting an unstable and weak, but locally focalized magma supply. Other features of this section include the absence of long-lived transforms, thick lithosphere, high upper mantle seismic wave velocities and thin oceanic crust (4-5 km).
When compared to other ridge segments, most MORB erupted along this section distinguish themselves by their higher Na2O, Sr and Al2O3 compositions, very low CaO/Al2O3 ratios relative to TiO2 and depleted heavy rare-earth element (REE) distributions. Another peculiar feature is their subparallel LREE enriched patterns. The high-Al-MgO magma type erupted periodically around the ridge system is also found in this region at 61.93°E. These lavas are characterized by high Al2O3 (> 17 wt. %), MgO (> 8.8 wt. %) and FeO contents, low SiO2 (< 49 wt. %) and Na2O and very low TiO2 (< 1 wt. %), and a LREE depleted pattern compared to the main population. At slightly lower MgO, sporadically, two other dredges located at 63.36-63.66°E share some of these distinct compositional characteristics. As a whole, these lavas are the most depleted in highly incompatible elements, but are also characterized by an offset toward lower MREE/HREE ratios relative to the main population.
These peculiar basalts are not parental to the more common lower MgO compositions and cannot be related to them by fractional crystallization alone. Instead, their major element features, and the occasional presence of positive Eu and Sr anomalies might indicate assimilation of plagioclase cumulates, while their offset in MREE/HREE might require a multistage melting evolution with an earlier event in the garnet stability field
Effect of melt/mantle interactions on MORB chemistry at the easternmost Southwest Indian Ridge (61 to 67°E)
No full textThe easternmost part of the Southwest Indian Ridge (61°-67°E) is an end-member of the global ridge system in terms of very low magma supply. As such, it is a good laboratory to investigate the effect of melt/mantle interactions on the composition of erupted basalts: for a given volume of erupted basaltic melt, the volume of reacted mantle is potentially greater than at more magmatically robust ridges. We analyzed major, trace element and isotopic compositions in three groups of rocks: plagioclase-bearing ultramafic and gabbroic rocks dredged in nearly amagmatic spreading corridors; basalts from the sparse volcanic cover of these corridors (“ultramafic seafloor basalts”); and basalts dredged from the intervening, more volcanically active domains (“volcanic seafloor basalts”). Ultramafic seafloor basalts have significantly lower CaO and Al2O3 contents at a given MgO than most volcanic seafloor basalts. We propose that both types of basalts are derived from similar parental melts, but that the ultramafic seafloor basalts are more affected by reactions between these parent melts and the mantle rocks in the lithosphere below the ridge. We infer that these reactions occur in the walls of conduits that allow the aggregated melts extracted from the melting mantle to rise through the axial lithosphere and to the eruption sites. The principal effect of these reactions is to enrich the asthenospheric melts in MgO through olivine dissolution. This effect is not expected to be as noticeable, but could still play a role in basalt petrogenesis at more magmatic regions of the global slow-spreading MOR system
Etude d'une image Seabeam de la dorsale est-indienne à 27° 40' S (océan Indien). 1 . Traitement et analyse de l'image. Seabeam investigation of the Southeast Indian Ridge at 27° 40' S (Indian Ocean). 1. Image processing
No full textA set of image processing is presented which allows to study with a great detail and without subjectivity a Seabeam bathymétrie grid of the axis of the Southeast Indian Ridge at 27°40'S. Three main operations are performed : the non covered points inside the Seabeam swaths of the grid are filled by linear interpolation ; the more than 20° slopes, corresponding to faults, are characterized and mapped. Finally, an autocorrelation process allows to estimate the pseudo-periodicity of the faults. A preliminary morphostructural interpretation of these processed images is proposed in a companion paper (Humler et al., 1988).Une série de traitements d'images est décrite afin de permettre une interprétation morphostructurale précise et non subjective d'une grille bathymétrique Seabeam (1000 * 1000 au pas de 120 m) obtenue à l'axe de la dorsale est-indienne à 27°40'S. La procédure de traitement de l'image Seabeam consiste en trois opérations majeures : un prétraitement permet de remplir par interpolation linéaire des lacunes à l'intérieur des zones couvertes par les faisceaux Seabeam ; les fortes pentes (supérieures à 20°) assimilées à des failles sont caractérisées et quantifiées ; enfin, un traitement d'autocorrélation permet une estimation de la pseudo-périodicité des failles. Une interprétation morphostructurale préliminaire de ces traitements fait l'objet d'un article séparé (Humler et al., 1988).Sauter Daniel, Humler Eric, Munschy Marc, Whitechurch Hubert, Schlich Roland, Ruhland Michel. Etude d'une image Seabeam de la dorsale est-indienne à 27° 40' S (océan Indien). 1 . Traitement et analyse de l'image. Seabeam investigation of the Southeast Indian Ridge at 27° 40' S (Indian Ocean). 1. Image processing. In: Sciences Géologiques. Bulletin, tome 41, n°2, 1988. Traitements d'images et objets géologiques. pp. 207-217
Prospective Terre Solide 2021-2025
No full textBilan et Prospective 2021-2025 de la Commission spécialisée Terre Solide de l‘Institut National des Sciences de l’UniversSynthèse des ateliers, des forums préparatoires et du colloque de Paris 19-21 octobre 2020Sous la coordination de Bruno Scaillet, Président de la CSTS, Eric Humler puis Stéphane Guillot,Directeur Adjoint Scientifique du domaine TS-INS
Prospective Terre Solide 2021-2025
No full textBilan et Prospective 2021-2025 de la Commission spécialisée Terre Solide de l‘Institut National des Sciences de l’UniversSynthèse des ateliers, des forums préparatoires et du colloque de Paris 19-21 octobre 2020Sous la coordination de Bruno Scaillet, Président de la CSTS, Eric Humler puis Stéphane Guillot,Directeur Adjoint Scientifique du domaine TS-INS
Prospective Terre Solide 2021-2025
No full textBilan et Prospective 2021-2025 de la Commission spécialisée Terre Solide de l‘Institut National des Sciences de l’UniversSynthèse des ateliers, des forums préparatoires et du colloque de Paris 19-21 octobre 2020Sous la coordination de Bruno Scaillet, Président de la CSTS, Eric Humler puis Stéphane Guillot,Directeur Adjoint Scientifique du domaine TS-INS
Prospective Terre Solide 2021-2025
No full textBilan et Prospective 2021-2025 de la Commission spécialisée Terre Solide de l‘Institut National des Sciences de l’UniversSynthèse des ateliers, des forums préparatoires et du colloque de Paris 19-21 octobre 2020Sous la coordination de Bruno Scaillet, Président de la CSTS, Eric Humler puis Stéphane Guillot,Directeur Adjoint Scientifique du domaine TS-INS
Prospective Terre Solide 2021-2025
No full textBilan et Prospective 2021-2025 de la Commission spécialisée Terre Solide de l‘Institut National des Sciences de l’UniversSynthèse des ateliers, des forums préparatoires et du colloque de Paris 19-21 octobre 2020Sous la coordination de Bruno Scaillet, Président de la CSTS, Eric Humler puis Stéphane Guillot,Directeur Adjoint Scientifique du domaine TS-INS
Prospective Terre Solide 2021-2025
No full textBilan et Prospective 2021-2025 de la Commission spécialisée Terre Solide de l‘Institut National des Sciences de l’UniversSynthèse des ateliers, des forums préparatoires et du colloque de Paris 19-21 octobre 2020Sous la coordination de Bruno Scaillet, Président de la CSTS, Eric Humler puis Stéphane Guillot,Directeur Adjoint Scientifique du domaine TS-INS
Prospective Terre Solide 2021-2025
No full textBilan et Prospective 2021-2025 de la Commission spécialisée Terre Solide de l‘Institut National des Sciences de l’UniversSynthèse des ateliers, des forums préparatoires et du colloque de Paris 19-21 octobre 2020Sous la coordination de Bruno Scaillet, Président de la CSTS, Eric Humler puis Stéphane Guillot,Directeur Adjoint Scientifique du domaine TS-INS
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