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Papers by Etienne Ruellan

<p>The George V and Tasman Transform Fault Systems (TFS) are major, right-stepping ... more <p>The George V and Tasman Transform Fault Systems (TFS) are major, right-stepping offsets of the South-East Indian Ridge between 140°E and 148°E. The George V TFS (~140°E) has an offset of about 300 km, and the Tasman TFS (~148°E) an offset of about 600 km. These TFS have multiple shear zones with intra-transform ridge segments (ITRS), mostly unmapped yet. We present the results of the analysis of geophysical and petrological data collected during the STORM cruise (South Tasmania Ocean Ridge and Mantle), completed with global data sets including satellite-derived gravity and bathymetry, and earthquake distribution. The swath bathymetry data cover some parts of the shear zones and only a few of ITRSs. They reveal a complex interaction between tectonic processes at the plate boundary and near-axis volcanic activity along and across the transform faults. In both the George V and Tasman TFS the western ITRS are shallower than the eastern ones, and they appear to receive a lot more magma supply. These western ITRS display off-axis volcanism observed on swath bathymetry or suspected from free-air gravity anomaly highs. In both TFS also, the western shear zone consists of two segments separated by a tectonic massif which we interpret to represent a push-up resulting from transpression along the transform. The mechanism involved in generating the transpression is a lengthening of the western ITRS to the west due to its high magma supply, leading to an overlap between the ITRS and the ridge segment immediately to the west of the TFS, that is in a mechanism similar to the processes currently uplifting the mylonitic massif along the St. Paul TF in the Equatorial Atlantic. The bathymetric and backscatter maps of the western George V TFS also reveal a series of recent off-axis oblique volcanic ridges. Rocks dredged on one of these ridges consist of picrites (i.e. basalts rich in olivine phenocrysts). These observations suggest that both TFS are not magma starved like many mid-ocean ridge transforms, but are the locus of significant primitive melt supply. Such an unexpected production of high-Mg melt might be related to the presence of a mantle thermal anomaly beneath the easternmost SEIR, the result of regional extension following clockwise rotations of the spreading direction, and/or to a western flow of mantle across the TFS. Some of the ITRS actually appeared after changes in the Australia-Antarctic plate motion.</p>

Oceanologica Acta, Special issue, 1985

The Mazagan (El Jadida) plateau and escarpment constitute the seaward extension of the Moroccan M... more The Mazagan (El Jadida) plateau and escarpment constitute the seaward extension of the Moroccan Meseta. Sedimentary sequence began at least as long ago as the Triassic. A very dense seismic reflection survey (32 profiles at 1 n. mile spacing) and information from 18 Cyana dives on the Mazagan the construction of isochrom map of the depth of the acoustic basement constituted either by jurassic platform carbonates or by Paleozoic granodiorite to Precambrian (?) crystalline basement, and a detailed structural map. The carbonate platform is structured in a succession of tilted blocks from the plateau to the foot of the escarpment. During early Cretaceous times, an important phase of vertical structuration is marked by the denudation of the escarpment. Transgressive sediments of late Cretaceous age cover unconformably the carbonate platform along the outer edge of the Mazagan Plateau. Deformation observed within the sedimentary cover suggests vertical tectonism from late Cretaceous up to...

1995年10~11月に行われた「しんかい6500」のマヌス海盆潜航調査(日仏 New STA RM, ER計画)の際に、3ヵ所の高温熱水をまとめて採取し、化学組成を明らかにした。 3ヵ所の熱水... more 1995年10~11月に行われた「しんかい6500」のマヌス海盆潜航調査(日仏 New STA RM, ER計画)の際に、3ヵ所の高温熱水をまとめて採取し、化学組成を明らかにした。 3ヵ所の熱水は、それぞれ化学的に全く異なる性質を示した。Vienna Woodsの熱水(最高温 度302°C)は、玄武岩からなる海底面に林立する硬石膏-硫化物のチムニーから噴きだし、中央海嶺の 熱水とは似通った性質を示した。PACMANUS siteでは、石英安山岩の海底から最高温度26 8°Cのブラックスモーカーが観測された。ここでの熱水は、重金属元素に富み、またKに富みCaに乏し いという、Vienna Woods熱水とは正反対の性質を示した。一方、DESMOS siteの 熱水(最高温度120°C)は、低ph(2.1),高H2S(8.9mM),高SO4(32.8mM) という特徴を示し、マグマ起源のSO2やH2Sの影響をきわめて強く受けた特異な熱水であることが明 らかになった。 また、高精度現場型マンガン自動分析装置(GAMOS)を「しんかい6500」にほぼ常時搭載し、熱 水域直上のマンガン濃度分布、および熱水プルームの微細構造の検出に始めて成功した。

Comptes rendus de l' …, 1992

Résumé/Abstract La campagne YOKOSUKA 91 du sous-marin japonais Shinkai 6500 (octobre 1991) à eu p... more Résumé/Abstract La campagne YOKOSUKA 91 du sous-marin japonais Shinkai 6500 (octobre 1991) à eu pour objectif de retourner sur deux sites hydrothermaux de l'axe de l'a dorsale du Bassin Nord-Fidjien explorés en 1989 par le Nautile. On a pu montrer que les ...

Geology and submarine …, 1994

Geological Society, London, Special Publications, 1984

Summary The Gorringe Bank is a 200 km long structure, oriented NE-SW, located at the eastern end ... more Summary The Gorringe Bank is a 200 km long structure, oriented NE-SW, located at the eastern end of the Azores-Gibraltar line, at the Europe-Africa boundary. It consists of two mounts, Mount Gettysburg at the SW (−25 m) and Mount Ormond at the NE (−100 m). Previous works have shown that it corresponds to a section in oceanic mantle and crust. A recent expedition of the submersible SP 3000 CYANA (May-June 1981) has allowed us: (i) to confirm that Mount Gettysburg essentially consists of largely serpentinized peridotites. The study of two oriented samples collected in situ allows some inferences about the kinematics of emplacement for these ultramafics; (ii) to show that Mount Ormond is mostly composed of various gabbros corresponding to different stages of differentiation. All the samples are more or less recrystallized and display strong deformation from high-temperature mylonitization to low-temperature brecciation. Such a ubiquitous deformation is not common in ophiolite complexes and may be linked with the location of the bank at the Europe-Africa plate boundary; (iii) to observe two generations of undeformed dykes cutting the Ormond gabbros: the first one of dolerites genetically linked with the gabbros, the second of alkaline rocks, feeders of the more recent alkaline volcanics capping the mount.

Earth and …, 1995

La dorsale du bassin de Manus est subdivisée en 3 segments principaux encadrés par les zones de f... more La dorsale du bassin de Manus est subdivisée en 3 segments principaux encadrés par les zones de fracture Wuillaumez, Djaul et Weitin. La campagne Manusflux du programme Franco-Japonais New STARMER avait pour objectif l'exploration in situ, à l'aide du Shinkai-6500, des segments central et oriental de la dorsale et I'échantillonnage des sites hydrothermaux associés. Les 2 segments montrent une morphologie différente, un substratum soit basaltique, soit dacitique et tous les degrés d'activité hydrothermale depuis la diffusion de basse température jusquiau stade fumeurs noirs.

In the frame of the STARMER French-Japanese joint project, the Nautile and her mothership Le Nadi... more In the frame of the STARMER French-Japanese joint project, the Nautile and her mothership Le Nadir have explored two areas of the active North-Fiji Basin axis (SW Pacific) near the 16'40's triple junction. In the first area, located at the northern end of the N 15 ridge, the close relationship between fracturation and hydrothermalisin has been evidenced. An active site "the White Lady" has been studied. It is characterized by an anhydrite inade chimney and by transparent, low chlorinity, and 285°C teniperature fluids. Alive animals colonies constituded essentially by gastropodes, cirripeds and niussels have been observed. The second site, in the graben at the western end of the North Fiji fracture zone, shows an extinct volcanic activity relayed by active fissuration. The northern wall of the graben exhibits a continuous section of the upper part of the oceanic crust (massive jlows, dyke coniplex and pillows).

Wrench tectonics flip at oblique subduction. A model from New Zealand Saut de tectonique décrocha... more Wrench tectonics flip at oblique subduction. A model from New Zealand Saut de tectonique décrochante en subduction oblique. Un modèle néo-zélandais

In September-October 1982, a joint German-French project to explore the Mazagan (El Jadida) escar... more In September-October 1982, a joint German-French project to explore the Mazagan (El Jadida) escarpment and plateau was carried out with the French submersible sp 3000 Cyana . The main purpose of CYAMAZ cruise was to observe and sample the steepest part of the escarpment where previous works suggest that the oldest series (since Jurassic) of the infilling of the Central Atlantic Ocean are outcropping. In this paper the authors present the main outline and results of the eighteen dives operated during the CYAMAZ cruise. These results essentially concern the stratigraphy and structure of the sedimentary series outcropping along the Mazagan escarpment. The age of the sedimentary sequence ranges from Late Jurassic-Lower Neocomian until Plio-Pleistocene. Late Jurassic-Early Cretaceous sediments constitute the carbonate platform. They are covered with post platform sediments of differents ages and facies. Observations from the submersible allow us to define two main directions of faulting ...

<p>The George V and Tasman Transform Fault Systems (TFS) are major, right-stepping ... more <p>The George V and Tasman Transform Fault Systems (TFS) are major, right-stepping offsets of the South-East Indian Ridge between 140°E and 148°E. The George V TFS (~140°E) has an offset of about 300 km, and the Tasman TFS (~148°E) an offset of about 600 km. These TFS have multiple shear zones with intra-transform ridge segments (ITRS), mostly unmapped yet. We present the results of the analysis of geophysical and petrological data collected during the STORM cruise (South Tasmania Ocean Ridge and Mantle), completed with global data sets including satellite-derived gravity and bathymetry, and earthquake distribution. The swath bathymetry data cover some parts of the shear zones and only a few of ITRSs. They reveal a complex interaction between tectonic processes at the plate boundary and near-axis volcanic activity along and across the transform faults. In both the George V and Tasman TFS the western ITRS are shallower than the eastern ones, and they appear to receive a lot more magma supply. These western ITRS display off-axis volcanism observed on swath bathymetry or suspected from free-air gravity anomaly highs. In both TFS also, the western shear zone consists of two segments separated by a tectonic massif which we interpret to represent a push-up resulting from transpression along the transform. The mechanism involved in generating the transpression is a lengthening of the western ITRS to the west due to its high magma supply, leading to an overlap between the ITRS and the ridge segment immediately to the west of the TFS, that is in a mechanism similar to the processes currently uplifting the mylonitic massif along the St. Paul TF in the Equatorial Atlantic. The bathymetric and backscatter maps of the western George V TFS also reveal a series of recent off-axis oblique volcanic ridges. Rocks dredged on one of these ridges consist of picrites (i.e. basalts rich in olivine phenocrysts). These observations suggest that both TFS are not magma starved like many mid-ocean ridge transforms, but are the locus of significant primitive melt supply. Such an unexpected production of high-Mg melt might be related to the presence of a mantle thermal anomaly beneath the easternmost SEIR, the result of regional extension following clockwise rotations of the spreading direction, and/or to a western flow of mantle across the TFS. Some of the ITRS actually appeared after changes in the Australia-Antarctic plate motion.</p>

Oceanologica Acta, Special issue, 1985

The Mazagan (El Jadida) plateau and escarpment constitute the seaward extension of the Moroccan M... more The Mazagan (El Jadida) plateau and escarpment constitute the seaward extension of the Moroccan Meseta. Sedimentary sequence began at least as long ago as the Triassic. A very dense seismic reflection survey (32 profiles at 1 n. mile spacing) and information from 18 Cyana dives on the Mazagan the construction of isochrom map of the depth of the acoustic basement constituted either by jurassic platform carbonates or by Paleozoic granodiorite to Precambrian (?) crystalline basement, and a detailed structural map. The carbonate platform is structured in a succession of tilted blocks from the plateau to the foot of the escarpment. During early Cretaceous times, an important phase of vertical structuration is marked by the denudation of the escarpment. Transgressive sediments of late Cretaceous age cover unconformably the carbonate platform along the outer edge of the Mazagan Plateau. Deformation observed within the sedimentary cover suggests vertical tectonism from late Cretaceous up to...

1995年10~11月に行われた「しんかい6500」のマヌス海盆潜航調査(日仏 New STA RM, ER計画)の際に、3ヵ所の高温熱水をまとめて採取し、化学組成を明らかにした。 3ヵ所の熱水... more 1995年10~11月に行われた「しんかい6500」のマヌス海盆潜航調査(日仏 New STA RM, ER計画)の際に、3ヵ所の高温熱水をまとめて採取し、化学組成を明らかにした。 3ヵ所の熱水は、それぞれ化学的に全く異なる性質を示した。Vienna Woodsの熱水(最高温 度302°C)は、玄武岩からなる海底面に林立する硬石膏-硫化物のチムニーから噴きだし、中央海嶺の 熱水とは似通った性質を示した。PACMANUS siteでは、石英安山岩の海底から最高温度26 8°Cのブラックスモーカーが観測された。ここでの熱水は、重金属元素に富み、またKに富みCaに乏し いという、Vienna Woods熱水とは正反対の性質を示した。一方、DESMOS siteの 熱水(最高温度120°C)は、低ph(2.1),高H2S(8.9mM),高SO4(32.8mM) という特徴を示し、マグマ起源のSO2やH2Sの影響をきわめて強く受けた特異な熱水であることが明 らかになった。 また、高精度現場型マンガン自動分析装置(GAMOS)を「しんかい6500」にほぼ常時搭載し、熱 水域直上のマンガン濃度分布、および熱水プルームの微細構造の検出に始めて成功した。

Comptes rendus de l' …, 1992

Résumé/Abstract La campagne YOKOSUKA 91 du sous-marin japonais Shinkai 6500 (octobre 1991) à eu p... more Résumé/Abstract La campagne YOKOSUKA 91 du sous-marin japonais Shinkai 6500 (octobre 1991) à eu pour objectif de retourner sur deux sites hydrothermaux de l'axe de l'a dorsale du Bassin Nord-Fidjien explorés en 1989 par le Nautile. On a pu montrer que les ...

Geology and submarine …, 1994

Geological Society, London, Special Publications, 1984

Summary The Gorringe Bank is a 200 km long structure, oriented NE-SW, located at the eastern end ... more Summary The Gorringe Bank is a 200 km long structure, oriented NE-SW, located at the eastern end of the Azores-Gibraltar line, at the Europe-Africa boundary. It consists of two mounts, Mount Gettysburg at the SW (−25 m) and Mount Ormond at the NE (−100 m). Previous works have shown that it corresponds to a section in oceanic mantle and crust. A recent expedition of the submersible SP 3000 CYANA (May-June 1981) has allowed us: (i) to confirm that Mount Gettysburg essentially consists of largely serpentinized peridotites. The study of two oriented samples collected in situ allows some inferences about the kinematics of emplacement for these ultramafics; (ii) to show that Mount Ormond is mostly composed of various gabbros corresponding to different stages of differentiation. All the samples are more or less recrystallized and display strong deformation from high-temperature mylonitization to low-temperature brecciation. Such a ubiquitous deformation is not common in ophiolite complexes and may be linked with the location of the bank at the Europe-Africa plate boundary; (iii) to observe two generations of undeformed dykes cutting the Ormond gabbros: the first one of dolerites genetically linked with the gabbros, the second of alkaline rocks, feeders of the more recent alkaline volcanics capping the mount.

Earth and …, 1995

La dorsale du bassin de Manus est subdivisée en 3 segments principaux encadrés par les zones de f... more La dorsale du bassin de Manus est subdivisée en 3 segments principaux encadrés par les zones de fracture Wuillaumez, Djaul et Weitin. La campagne Manusflux du programme Franco-Japonais New STARMER avait pour objectif l'exploration in situ, à l'aide du Shinkai-6500, des segments central et oriental de la dorsale et I'échantillonnage des sites hydrothermaux associés. Les 2 segments montrent une morphologie différente, un substratum soit basaltique, soit dacitique et tous les degrés d'activité hydrothermale depuis la diffusion de basse température jusquiau stade fumeurs noirs.

In the frame of the STARMER French-Japanese joint project, the Nautile and her mothership Le Nadi... more In the frame of the STARMER French-Japanese joint project, the Nautile and her mothership Le Nadir have explored two areas of the active North-Fiji Basin axis (SW Pacific) near the 16'40's triple junction. In the first area, located at the northern end of the N 15 ridge, the close relationship between fracturation and hydrothermalisin has been evidenced. An active site "the White Lady" has been studied. It is characterized by an anhydrite inade chimney and by transparent, low chlorinity, and 285°C teniperature fluids. Alive animals colonies constituded essentially by gastropodes, cirripeds and niussels have been observed. The second site, in the graben at the western end of the North Fiji fracture zone, shows an extinct volcanic activity relayed by active fissuration. The northern wall of the graben exhibits a continuous section of the upper part of the oceanic crust (massive jlows, dyke coniplex and pillows).

Wrench tectonics flip at oblique subduction. A model from New Zealand Saut de tectonique décrocha... more Wrench tectonics flip at oblique subduction. A model from New Zealand Saut de tectonique décrochante en subduction oblique. Un modèle néo-zélandais

In September-October 1982, a joint German-French project to explore the Mazagan (El Jadida) escar... more In September-October 1982, a joint German-French project to explore the Mazagan (El Jadida) escarpment and plateau was carried out with the French submersible sp 3000 Cyana . The main purpose of CYAMAZ cruise was to observe and sample the steepest part of the escarpment where previous works suggest that the oldest series (since Jurassic) of the infilling of the Central Atlantic Ocean are outcropping. In this paper the authors present the main outline and results of the eighteen dives operated during the CYAMAZ cruise. These results essentially concern the stratigraphy and structure of the sedimentary series outcropping along the Mazagan escarpment. The age of the sedimentary sequence ranges from Late Jurassic-Lower Neocomian until Plio-Pleistocene. Late Jurassic-Early Cretaceous sediments constitute the carbonate platform. They are covered with post platform sediments of differents ages and facies. Observations from the submersible allow us to define two main directions of faulting ...