Two samples of a granodiorite and a hypersthene granodiorite provided a unique opportunity to investigate the nature of the basement of the Mazagan Escarpment, the northwestern margin of continental ...Africa (Morocco) on a steep part of the lower continental slope in offshore Morocco. We conducted U–Pb LA-ICPMS geochronology on zircon from the granodiorite, which was acquired from a deep sea drilling program core DSDP544, and on zircon and monazite from a hypersthene granodiorite collected previously during the Cyamaz submersible campaign, to determine the ages of the rocks of the Mazagan Escarpment and interpret their origins. Zircon from the granodiorite yielded a 556 ± 10 Ma crystallization age, abundant inherited zircon cores up to 620 Ma and three ~2.68, ~1.76 and ~1.20 Ga cores. The hypersthene granodiorite yielded ~1950–1750 Ma zircon and ~1820–1640 Ma monazite ages. Some rocks of the closest onshore continental platform have recently been interpreted as belonging to an exotic Avalonian terrane, and correlated with the Mazagan Escarpment. Our data do not provide evidence that the Mazagan Escarpment is part of an exotic terrane. It is more likely that the hypersthene granodiorite formed in an extensional setting after the 2.25–2.07 Ga Eburnean orogeny, at a time of otherwise predominantly mafic magmatism that may have caused magmatic underplating and heating from below. The granodiorite formed during the late Ediacaran, which is characterized by widespread magmatism in Northwest Africa. Therefore, it is likely that the rocks of the Mazagan Escarpment have a Northwest African origin, which implies that the Pangean suture zone lies west of it.
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•Basement rocks of the Mazagan Escarpment, were analyzed to interpret their ages and potential origins.•Granodiorite yielded a 556 ± 10 Ma crystallization age and a hypersthene granodiorite yielded ~1950–1750 Ma zircon and ~1820–1640 Ma monazite ages.•The basement rocks of the Mazagan Escarpment most likely have a Northwest African origin.
Using a combined approach of seafloor mapping, MAPR and CTD survey, we report evidence for active hydrothermal venting along the 130°‐140°E section of the poorly‐known South‐East Indian Ridge (SEIR) ...from the Australia‐Antarctic Discordance (AAD) to the George V Fracture Zone (FZ). Along the latter, we report Eh and CH4 anomalies in the water column above a serpentinite massif, which unambiguously testify for ultramafic‐related fluid flow. This is the first time that such circulation is observed on an intermediate‐spreading ridge. The ridge axis itself is characterized by numerous off‐axis volcanoes, suggesting a high magma supply. The water column survey indicates the presence of at least ten distinct hydrothermal plumes along the axis. The CH4:Mn ratios of the plumes vary from 0.37 to 0.65 denoting different underlying processes, from typical basalt‐hosted to ultramafic‐hosted high‐temperature hydrothermal circulation. Our data suggest that the change of mantle temperature along the SEIR not only regulates the magma supply, but also the hydrothermal activity. The distribution of hydrothermal plumes from a ridge segment to another implies secondary controls such as the presence of fractures and faults along the axis or in the axial discontinuities. We conclude from these results that hydrothermal activity along the SEIR is controlled by magmatic processes at the regional scale and by the tectonics at the segment scale, which influences the type of hydrothermal circulation and leads to various chemical compositions. Such variety may impact global biogeochemical cycles, especially in the Southern Ocean where hydrothermal venting might be the only source of nutrients.
Key Points
Intense and contrasted hydrothermal activity has been evidenced along the South‐East Indian Ridge in the Furious Fifties
Ultramafic circulation is evidenced in the George V FZ, which is the first observation of this type along an intermediate‐spreading ridge
Chemical compositions of the plumes reveal various regional and local controls on the hydrothermal circulation
Abstract
Using a combined approach of seafloor mapping, MAPR and CTD survey, we report evidence for active hydrothermal venting along the 130°‐140°E section of the poorly‐known South‐East Indian ...Ridge (SEIR) from the Australia‐Antarctic Discordance (AAD) to the George V Fracture Zone (FZ). Along the latter, we report Eh and CH
4
anomalies in the water column above a serpentinite massif, which unambiguously testify for ultramafic‐related fluid flow. This is the first time that such circulation is observed on an intermediate‐spreading ridge. The ridge axis itself is characterized by numerous off‐axis volcanoes, suggesting a high magma supply. The water column survey indicates the presence of at least ten distinct hydrothermal plumes along the axis. The CH
4
:Mn ratios of the plumes vary from 0.37 to 0.65 denoting different underlying processes, from typical basalt‐hosted to ultramafic‐hosted high‐temperature hydrothermal circulation. Our data suggest that the change of mantle temperature along the SEIR not only regulates the magma supply, but also the hydrothermal activity. The distribution of hydrothermal plumes from a ridge segment to another implies secondary controls such as the presence of fractures and faults along the axis or in the axial discontinuities. We conclude from these results that hydrothermal activity along the SEIR is controlled by magmatic processes at the regional scale and by the tectonics at the segment scale, which influences the type of hydrothermal circulation and leads to various chemical compositions. Such variety may impact global biogeochemical cycles, especially in the Southern Ocean where hydrothermal venting might be the only source of nutrients.
Key Points
Intense and contrasted hydrothermal activity has been evidenced along the South‐East Indian Ridge in the Furious Fifties
Ultramafic circulation is evidenced in the George V FZ, which is the first observation of this type along an intermediate‐spreading ridge
Chemical compositions of the plumes reveal various regional and local controls on the hydrothermal circulation
In eastern North Island New Zealand, oblique subduction of the Pacific Plate beneath the Australian Plate is associated with strain partitioning. Dextral along-strike component of displacement ...occurred first at Early Miocene major faults within the eastern fore-arc domain. These faults were active from Early Miocene to Pliocene times. Since Pliocene times, most of the movement occurs at western faults such as the Wellington Fault. The latter joins the back-arc domain to the north. The jump of wrench faulting is related to the oblique opening of the back-arc domain. Both phenomena are impeded southwards by the Hikurangi oceanic plateau entering the subduction zone.
To cite this article: J. Delteil et al., C. R. Geoscience 335 (2003).
Dans l'ı̂le nord de Nouvelle-Zélande, la subduction oblique de la plaque pacifique sous la plaque australienne est accommodée par un partitionnement du mouvement. Les premiers décrochements dextres sont apparus dans le domaine avant-arc oriental au Miocène inférieur. Depuis le Pliocène, la plupart des coulissements se produisent à l'ouest, en particulier sur la faille de Wellington, qui se connecte vers le nord au domaine arrière-arc. Ce saut de la tectonique décrochante vers l'arrière-arc est lié à l'ouverture oblique du domaine arrière-arc. Les deux phénomènes sont bloqués au sud par l'arrivée du plateau océanique de Hikurangi dans la zone de subduction.
Pour citer cet article : J. Delteil et al., C. R. Geoscience 335 (2003).
The continental slope offshore Nice is a natural laboratory to investigate submarine landslides and gravity-flow processes. Using EM300 bathymetry data (spatial resolution of 25 m), about 250 scars ...with volume less than 8 × 108 m3 were identified. The AUV bathymetric data (spatial resolution of 2 m) revealed a greater number of scar-related failures with two main morphologies: some scars are affected by retrogressive processes of erosion, suggesting failures were triggered a long time ago, while other scars exhibit no evidence of post-failure erosion, suggesting they could have been triggered recently. Downslope from the scars, there are scattered blocks, on average 5-m high and 40-m wide, and well-developed asymmetrical waves, on average 2-m high and 20-m in wavelength. Such evolution could be evidence for the transformation of the remobilized deposits into cohesive flows then turbulent flows. Such transformation took place over a distance of less than 6–8 km.
Dans le Sud-Ouest Pacifique, la configuration de la frontière convergente entre les plaques Australie et Pacifique est le résultat d’interactions complexes s’exerçant sur un vaste domaine de ...déformation active entre deux subductions à vergences opposées et les ouvertures d’arrière-arc qui leur sont associées. À l’est, la plaque Pacifique subducte vers l’ouest dans la fosse de Tonga-Kermadec, et à l’ouest, la plaque Australie plonge vers le nord-est dans la fosse du Vanuatu-Salomon. Y sont associées respectivement les ouvertures des bassins de Lau-Havre et Nord-Fidjien. La liaison entre les deux subductions est un domaine à déformation diffuse, composé de multiples centres d’accrétion actifs relayés par des failles transformantes. La bordure nord est matérialisée par la subduction de Vitiaz, inactive depuis le Miocène supérieur, le long de laquelle la lithosphère Pacifique crétacée passait sous la plaque Australie. L’ouverture océanique consécutive du bassin Nord Fidjien débute, il y a environ 12 Ma, et se développe le long de plusieurs axes d’accrétion contrastés. L’accrétion dans le bassin de Lau est plus récente et plus localisée. Les liens entre subduction et accrétion océanique d’arrière-arc sont partout évidents dans la région, et tout particulièrement dans le bassin de Lau. Cependant, on relève une multiplication anormale des axes d’accrétion actifs à la jonction entre les deux bassins. Cette situation géodynamique, tectonique, magmatique et géochimique complexe, voire anormale, de même que l’anomalie positive de la topographie et du géoïde, la présence d’un fort flux de chaleur, d’une lithosphère océanique mince et de faibles vitesses mantelliques témoignent tous d’une convection intense dans le manteau supérieur sous l’ensemble de la frontière, et d’une influence de type point chaud étendu dans la partie septentrionale.
In eastern North Island New Zealand, oblique subduction of the Pacific Plate beneath the Australian Plate is associated with strain partitioning. Dextral along-strike component of displacement ...occurred first at Early Miocene major faults within the eastern fore-arc domain. These faults were active from Early Miocene to Pliocene times. Since Pliocene times, most of the movement occurs at western faults such as the Wellington Fault. The latter joins the back-arc domain to the north. The jump of wrench faulting is related to the oblique opening of the back-arc domain. Both phenomena are impeded southwards by the Hikurangi oceanic plateau entering the subduction zone.
La Terre sous l’Océan Association Internationale des Géomorphologues; Huguen, Caroline; Lagabrielle, Yves ...
Géomorphologie : revue du Groupe français de géomorphologie,
2005, Letnik:
11, Številka:
2
Journal Article
A surface ship gravity survey was carried out in the northern part of the North Fiji Basin during the NOFI cruise by the R/V l'Atalante in August-September, 1994. The two ridges inside the study ...area, the South Pandora Ridge and the Tripartite Ridge, present different structures and states of isostatic equilibrium in terms of gravity anomaly and its tectonic implications. The former is supported by a restoring force of an imaginary elastic plate in the crust and the latter by the Airy type isostasy. These characteristics can be derived from the difference in magmatic activity, as influenced by the difference in lithospheric structure. The latter is characterised by greater active magmatism and hydrothermalism underneath the ridge than the former. Such a difference in the magmatic activity and the horizontal scale of the shallow subsurface structure is derived from the difference in the stiffness or viscosity of the lithosphere beneath the two ridges.PUBLICATION ABSTRACT
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