26 research outputs found
L'extrémité occidentale de la zone de fracture fidjienne et le point triple de 16°40S-résultats du leg III de la campagne SEAPSO du N.O. Jean-Charcot (décembre 1985) dans le bassin nord-Fidjien (SW Pacifique)
Au cours du leg III de la campagne SEAPSO du N.O. Jean-Charcot, à été réalisé un levé géophysique et bathymétrique Seabeam de l'extrémité occidentale de la fracture nord-Fidjienne, à la jonction avec la dorsale du bassin nord-Fidjien. Une étude détaillée de ce levé permet de mettre en évidence un réarrangement récent de la direction du systÚme d'accrétion de part et d'autre de cette jonction, accompagné du fonctionnement synchrone d'un point triple centré sur 16°40S. (Résumé d'auteur
ContrÎle karstique de minéralisations nickélifÚres de Nouvelle-Calédonie
International audienceFracturing associated with the nickeliferous mineralisations of New Caledonia has been successively considered as pre-dating and then post-dating the metallogenic processes. On the basis of a study of the dynamics of karst contemporaneous with lateritisation, a new emplacement model is proposed for the mineralisation: a network of hydraulic fractures of the crack-seal type governs the emplacement of mineralisation, associated with a network of normal faults that controls the sinking and evacuation of the karst productsLa fracturation associée aux minéralisations nickélifÚres de Nouvelle-Calédonie a successivement été considérée comme antérieure, puis postérieure, au processus métallogénique. à la suite d'une étude des processus dynamiques du karst contemporain de la latéritisation, nous proposons un nouveau modÚle de mise en place des minéralisations. Dans ce modÚle, la minéralisation se met en place par l'intermédiaire d'un réseau de fractures hydrauliques de type crack-seal, associé à un réseau de failles normales qui guident l'enfoncement et l'évacuation des produits du karst
Evidence for sinistral strike-slip deformation in the Solomon Island arc
6 pages, 4 figuresDuring the SOPACMAPS 2 crusie carried out by IFREMER (Institut Français de Recherche pour l'Exploitation de la Mer) and ORSTOM (Institut Français de Recherche Scientifique pour le dévelopement en Coopération) on theR/V L'Atalante, in the Central Solomon Arc area, multibeam bathymetric and imagery data and single-channel seismic reflection profiles were collected from an area of about 3500 km2, to evaluate regional tectonics. Structural data geophysical profiles interpretation provide evidence for left-lateral transtensional tectonics on the southern edge of the Central Solomon Trough. This transtensional deformation is represented by faulting, block tilting, and rhombohedral deformation. The regional geology and the analysis of the sedimentary cover allow us to demonstrate that this tectonic occurred in two different phases during Oligocene to Miocene and Pliocene to Pleistocene timesPeer reviewe
Tectonic history of northern New Caledonia Basin from deep offshore seismic reflection: Relation to late Eocene obduction in New Caledonia, southwest Pacific
International audienceNew, high-quality multichannel seismic reflection data from the western New Caledonia offshore domain allow for the first time the direct, continuous connection of seismic reflectors between the Deep Sea Drilling Project 208 drill hole on the Lord Howe Rise and the New Caledonia Basin. A novel seismic interpretation is hence proposed for the northern New Caledonia Basin stratigraphy, which places the Eocene/Oligocene unconformity deeper than previously thought and revisits the actual thickness of the pre-Oligocene sequences. A causal link is proposed between the obduction of the South Loyalty Basin over New Caledonia (NC) and the tectonic history of the northern New Caledonia Basin. Here it is suggested that as the South Loyalty Basin was being obducted during early Oligocene times, the NC Basin subsided under the effect of the overloading and underthrusted to accommodate the compressional deformation, which resulted in (1) the uplift of the northern Fairway Ridge and (2) the sinking of the western flank of New Caledonia. This event also had repercussions farther west with the incipient subsidence of the Lord Howe Rise
Evolution geodynamique des bassins marginaux Nord Fidjien et de Lau (sud-ouest Pacifique)
SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
Ăvolution gĂ©odynamique du domaine Ouest-offshore de la Nouvelle-CalĂ©donie et de ses extensions vers la Nouvelle-ZĂ©lande
Le Sud-Ouest Pacifique est le résultat de la fragmentation de la marge Est du Gondwana depuis le Crétacé. L objet du présent travail de thÚse est d approfondir la connaissance des bassins de Nouvelle-Calédonie et de Fairway, situés à l Ouest de la NC, afin de préciser l évolution géodynamique du SO Pacifique du Crétacé à l OligocÚne. L analyse de nouvelles données géophysiques a permis de dégager 3 étapes de cette fragmentation : 1.Formation du Bassin de Fairway-Aotea au Crétacé moyen en position intra-arc continental. La formation de ce bassin reflÚte les prémices de la déchirure continentale de la marge Est Gondwanienne dont la cause est à rechercher dans un changement de la dynamique de h subduction. 2. Déformation locale de la partie Nord du BNC à l EocÚne terminal synchrone à l obduction Néo Calédonienne. Nous proposons ainsi un modÚle selon lequel le BNC aurait subsidé et réagi comme un bassin flexural d avant-pays suivant un processus de sous-charriage, au fur et à mesure que h nappe progressait sur le bùti Calédonien. 3. Subsidence EocÚne OligocÚne régionale affectant les structures reliant la Nouvelle-Zélande à la NC. Les traits morphostructuraux de cette déformation nous permettent d émettre l hypothÚse que l ablation d une partie de la croûte inférieure de ce systÚme serait responsable de h subsidence. Nous proposons ainsi un modÚle dans lequel la reprise de la convergence vers 45 Ma entre les plaques Australienne et Pacifique aurait entraßné un épaississement crustal de l ensemble aboutissant à une instabilité gravitaire de sa racine et provoquant son détachement dans le manteau. Ces nouveaux résultats ont des implications pour le potentiel pétrolier régional.The southwest Pacific results from the fragmentation of Gondwanaland since the Cretaceous time. The purpose of the current PhD work is to deepen our understanding of the history of the New Caledonia and Fairway basins, located west of New Caledonia, in order to better constrain the geodynamical evolution of the SW Pacific from Cretaceous to Oligocene. The analysis of new geophysical data has led to distinguish 3 main phases of this fragmentation : 1. Mid Cretaceous formation of the Fairway-Aotea Basin in a continental intra-arc position. The formation of this basin reflects the initial stage of continental fragmentation of the Eastern Gondwana margin. The causes of this fragmentation are to be searched for in a major change of the dynamics of the peri-Pacific subduction zone. 2. Latest late Eocene local deformation of the Northern NCB, synchronously with the New Caledonian obduction. We suggest that as the ophiolitic nappe was being obducted onto New Caledonia, the NC Basin subsided under the effect of the loading and underthrusted to accommodate the compressional deformation as a foreland flexural basin. Regional Eocene Oligocene subsidence of the structures linking NC to New Zealand. The morphostructural style of this deformation leads us to suggest that detachment of the lower crust is the cause of subsidence. We therefore propose a model in which the renewal of the Australia-Pacific convergent plate boundary around 45 Ma would have driven the lithosphere to thicken, leading to a root instability and to its detachment in the mantle. These newresults have regional petroleum implications, which are discussed in the PhD.BREST-BU Droit-Sciences-Sports (290192103) / SudocPLOUZANE-Bibl.La Pérouse (290195209) / SudocSudocFranceF
Showcasing the sovereignty of non-self-governing islands: New Caledonia
International audienc
The Loyalty-New Hebrides Arc collision: Effects on the Loyalty Ridge and basin system, Southwest Pacific (first results of the ZoNĂ©Co programme)
The ZoNĂ©Co 1 and 2 cruises of Ifremer's Research Vessel L'Atalante, collected new swath bathymetry and geophysical data over the southern and northern segments of the basins and ridges forming the Loyalty system. Between the two surveyed areas, previous studies found evidence for the resistance of the Loyalty Ridge to subduction beneath the New Hebrides trench near 22°Sâ169°E. On the subducted plate, except for seismicity related to the downbending of the Australian plate, recorded shallow seismicity is sparse within the Loyalty system (Ridge and Basin) where reliable focal mechanism solutions are almost absent. Swath bathymetry, seismic reflection and magnetic data acquired during the ZoNĂ©Co 1 and 2 cruises revealed a transverse asymmetric morphology in the Loyalty system, and an along-strike horst and graben structure on the discontinuous Loyalty Ridge. South of 23°50primeS and at 20°S, the two WSW-ENE-trending fault systems, respectively, sinistral and dextral, that crosscut the southern and northern segments of the Loyalty system, are interpreted as due to the early effects of collision with the New Hebrides Arc. A NNW-SSE trend, evident along the whole Loyalty system and on the island of New Caledonia, is interpreted as an inherited structural trend that may have been reactivated through flexure of the Australian lithospheric plate at the subduction zone. Overall then, the morphology, structure and evolution of the southern and northern segments of the Loyalty system probably result from the combined effects of the Australian plate lithospheric bulge, the active Loyalty-New Hebrides collision and the overthrust of the New Caledonian ophiolite
Les karsts latéritiques de Nouvelle-Calédonie
The lateritic karsts of New Caledonia. The metallogenetic role of karst phenomena is known for a long time.
The main ore bodies formed in this way contain aluminium, lead-zinc, nickel, or copper. In New Caledonia, the humid tropical climate was the reason for the development of various karst types within carbonate formations and ultramafic rocks of the Caledonian ophiolite. Nickel concentrated in altered pockets is mined since the 19th century. The genesis of the ore was debated controversially, and different geological models had been proposed. Initially, the ores were interpreted as being hydrothermal deposits. Then, they were considered supergene, with meteoric fluids using pre-existing fractures. They also were considered as being contemporaneous to radially expanding neotectonic activity. The lateritic alteration of the peridotites began on a Miocene paleosurface.
By means of a structural analysis, we show that the listric faults containing the mineralisation are due to karstic collapses. A detailed analysis of the complete karst buildup is made, where hydrauic fracturing plays a dominant role in the dynamics and structurisation of the karst.Le rĂŽle mĂ©tallogĂ©nique des phĂ©nomĂšnes karstiques est connu de longue date. Les principaux gisements ainsi formĂ©s concernent l'aluminium, le plomb-zinc, le nickel et le cuivre. En Nouvelle-CalĂ©donie, le climat tropical humide a dĂ©veloppĂ© divers types de karsts dans les formations carbonatĂ©es et dans les roches ultramafiques de l'ophiolite calĂ©donien. Le nickel concentrĂ© dans les profils d'altĂ©ration est exploitĂ© depuis le XIXĂšme siĂšcle. La mise en place de ces gisements a fait l'objet de nombreuses controverses. Divers modĂšles gĂ©ologiques ont Ă©tĂ© proposĂ©s au cours du temps. Ils ont initialement Ă©tĂ© interprĂ©tĂ©s comme d'origine hydrothermale. On les a ensuite considĂ©rĂ©s comme supergĂšnes oĂč les fluides mĂ©tĂ©oriques empruntent des rĂ©seaux de fractures prĂ©existantes. Ils ont Ă©galement Ă©tĂ© considĂ©rĂ©s comme contemporains d'une nĂ©otectonique en extension radiale. L'altĂ©ration latĂ©ritique des pĂ©ridotites s'est dĂ©veloppĂ©e Ă partir d'une palĂ©osurface d'Ăąge miocĂšne. Nous montrons par une analyse structurale que les failles listriques qui contiennent la minĂ©ralisation correspondent Ă des effondrements karstiques. Une analyse dĂ©taillĂ©e de l'ensemble de l'Ă©difice karstique est proposĂ©e, dans lequel la fracturation hydraulique a un rĂŽle dominant dans la dynamique et la structuration du karst.Genna Antonin, Bailly Laurent, Lafoy Yves, AugĂ© Thierry. Les karsts latĂ©ritiques de Nouvelle-CalĂ©donie. In: Karstologia : revue de karstologie et de spĂ©lĂ©ologie physique, n°45-46, AnnĂ©e 2005 2005. PalĂ©okarst des plateaux ardĂ©chois et Ressources en eau dans le Sud de Madagascar. pp. 19-28
Ăvolution gĂ©omorphologique de l'avant-pays du Sud-Ouest de la Nouvelle-CalĂ©donie durant les derniers cycles glaciaires
International audienceWe present the morphological analysis of a combined digital elevation model (DEM) obtained by merging data from terrestrial and coastal regions of southern New-Caledonia. Our aim is to describe the Quaternary morphotectonic evolution of the southwestern lagoon of New Caledonia, a region with a shallow average bathymetry (20 m), recently submerged in response to both tectonic and eustatic fluctuations. The marine DEM was obtained by interpolating 131â000 depth soundings from MOPâSHOM (âMission ocĂ©anographique du PacifiqueâââService hydrographique et ocĂ©anographique de la Marineâ, France). We confirm that morphologies such as meandering channels and deeply incised canyons are the result of a sub-aerial fluviatile evolution during periods of low sea levels. The marine sedimentation in this region is very recent, probably corresponding to no more than two glacialâinterglacial cycles. Geometrical relationships between submerged paleo-rivers and streams, including captures and incisions, strongly suggest that Quaternary active tectonics affected river development. We identify two hydrographic palaeo-networks suggesting outflow changes, from parallel to the present-day island axis to perpendicular.Nous prĂ©sentons les rĂ©sultats de l'analyse morphologique d'une compilation cartographique rĂ©alisĂ©e par fusion de modĂšle numĂ©rique de terrain marin et terrestre du Sud de la Nouvelle-CalĂ©donie. Le but de l'Ă©tude est de prĂ©ciser l'Ă©volution morphotectonique quaternaire du lagon sud-ouest en relation avec celle de l'avant-pays Ă©mergĂ©. Le MNT marin a Ă©tĂ© obtenu par interpolation de points de mesure de sonde provenant de minutes de bathymĂ©trie. Nous confirmons que la morphologie visible dans la bathymĂ©trie actuelle du lagon (profondeur moyenne : 20 m), rĂ©sulte d'une Ă©volution fluviatile aĂ©rienne en pĂ©riode de bas niveau marin. L'ennoiement de ce domaine est trĂšs rĂ©cent (deux cycles glaciaires probablement). Deux palĂ©o-rĂ©seaux hydrographiques sont mis en Ă©vidence, s'Ă©coulant parallĂšlement, puis perpendiculairement Ă l'axe actuel de l'Ăźle. Les relations gĂ©omĂ©triques entre les palĂ©o-fleuves, lacs et riviĂšres ennoyĂ©s suggĂšrent des modifications de sens d'Ă©coulement en relation avec des mouvements tectoniques rĂ©cents