The George V and Tasman Transform Fault Systems (TFS) are major, right-stepping offsets of the So... more 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 s...
We studied the east intersection between the Romanche transform fault (TF) and the Mid-Atlantic r... more We studied the east intersection between the Romanche transform fault (TF) and the Mid-Atlantic ridge using bathymetry and gravity anomalies, to investigate the temporal evolution of the ultra-cold ridge-transform intersection. Our results reveal a complex ridge axis, with evidence of a significant decrease in the along-axis melt supply towards the RTI but also since ~10 Ma.Over a 100 km distance south of the RTI, the ridge axis is formed by three spreading segments offset by large non-transform discontinuities. Large detachment faults mark the present-day spreading style at the RTI, while magma supply increases away from the Romanche intersection. Axial and near-axis fault patterns reveal a marked obliquity, especially in the north and center of the study area.In lithosphere older than 10 Ma, the ridge axis appears to form a single spreading segment between the Romanche and Chain TFs, perpendicular to the spreading direction, with relatively regular abyssal hills. From around 10 to...
At mid-oceanic ridges, mantle temperature and magma supply influence the structure of the neo-vol... more At mid-oceanic ridges, mantle temperature and magma supply influence the structure of the neo-volcanic zone. Due to the large Romanche offset, a strong “cold edge” effect is present at its eastern intersection with the Mid-Atlantic Ridge. This effect decreases with the distance from the transform fault, making this region an ideal area to study the impact of the thermal gradient on the architecture of the neo-volcanic zone. We analyzed seafloor videos and photos from submersible dives, as well as bathymetry and backscatter data collected during the SMARTIES cruise (2019), from the Ridge-Transform Intersection (RTI) to approximately 80 km to the south of it. We produced maps at local and regional scales and quantified the morphology of volcanoes (height, diameter, height/diameter ratio, volume and surface). Visual observations have showed that the seafloor is mainly made up of pillows or elongated pillows and rare massive lava flows. Within 30 km of the RTI, the neo-volcanic area is ...
We present data for glassy basalts from ~37 localities along the spreading axis of the Southeast ... more We present data for glassy basalts from ~37 localities along the spreading axis of the Southeast Indian Ridge (SEIR) between 126\ub0-140\ub0E, eastward of the Australian-Antarctic Discordance (AAD). Each of the five ridge segments (A1 to A5, west to east) show well-defined major element trends. An isotopic and negative axial depth anomaly is present, centered on the overlapping tips of segments A3 and A4 at ~135\ub0E. Segment A4 basalts have distinct radiogenic Pb and He isotopes plus enriched MORB-like \u3b5Hf, relative to segments to the west and east. Crystal fractionation is more extensive at the A3 and A5 overlapping segment tips adjacent to A4, and decreases both to the west and east. The along axis pattern suggests a mantle heterogeneity located beneath the A3-A4 segments. Pb-Pb isotopic co-variations for the 5 segments define two linear arrays, with a western trend (A1-A3) and an eastern trend (A4-A5) that intersects it at the composition of the anomalous A4 segment, at a 206Pb/204Pb ~ 19. The western trend has higher 208Pb/204Pb for a given 206Pb/204Pb, revealing a gradient in the asthenosphere, with 06208Pb/204Pb decreasing to the east away from the AAD. Overall, 206,207,208Pb/204Pb and 4He/3He of the A4 anomaly define trends that vector toward the fields for Cenozoic lavas from west Antarctica (Marie Byrd Land and Balleny Islands). West Antarctica has a history of mantle plume underplating and lithosphere modification by subduction [1,2], and there is a broad seismic anomaly below 250 km underlying the West Antarctic Rift system [3]. Our data supports a model in which flow of underplated material plus lithosphere may be guided by the underside topography of the lithosphere beneath the Transantarctic mountains. This flow emerges from beneath east Antarctica, where it leads to volcanism in the Balleny Islands [4]. The material apparently continues to flow northward to the SEIR at ~135\ub0E. The geochemical anomaly beneath Zone A is potentially explained by the presence of this residual plume/mobilized lithospheric material in the subridge mantle of the SEIR. [1] Hart et al., 1997, Chem Geol 139; [2] Aviado et al. 2015, G3 16; [3] Moelli and Danesi, 2004, GPC 42; [4] Sleep, 2006, ESR 77
Oceanic crust is formed by melt derived from the mantle at oceanic spreading centers. A small amo... more Oceanic crust is formed by melt derived from the mantle at oceanic spreading centers. A small amount of melting initiates at about 150-300 km depths in the presence of volatiles (CO2, H2O)1–3, but the extensive dry melting commences at 60-70 km depths due to the upwelling of the mantle as two diverging plates move apart4,5. However, how these melts migrate to the surface and what happens to these melts in the upper part of the mantle are still not understood. Using seismological data recorded by ocean-bottom seismometers, here we report the presence of deep earthquakes at 10-20 km depth in the hot mantle along the Mid-Atlantic Ridge axis, much below the brittle-ductile boundary, suggesting that these earthquakes are caused by a volume change associated with the CO2 degassing from the ascending melt. The geochemical analyses of basalts from the ridge axis show an abnormally high quantity of CO2 (>1.9 wt%) in the primitive melt, confirming the CO2 degassing hypothesis. The large co...
2015 IEEE/OES Acoustics in Underwater Geosciences Symposium (RIO Acoustics), 2015
The COLMEIA Project is an international collaboration between France and Brazil involving several... more The COLMEIA Project is an international collaboration between France and Brazil involving several universities and research institutes. One of the objectives of this project is to study the tectonic evolution and to understand the processes that result in the exhumation of the ultramafic body which composes the São Pedro e São Paulo archipelago, as wellasthe magmatism and tectonics of this part of the Mid-Atlantic Ridge, especially for the recent geologic time. The work is essential to understand the evolution of the Equatorial Atlantic Ocean. A fundamental part of thestudy targets the detailed analysis of sites that indicate recent off-axis deformation, since these faults could work as pathways for hydrothermal fluids, which is important to understand hydrothermalism in sediment environments. This paper presents the preliminary results of the analysis of the seismic data acquired during the COLMEIA cruise. The first step was to process the seismic lines in the north part of the area covered during the cruise, where the St. Peter peridotite ridge is located. The software used, Sispeed v5.5, was developed by the IFREMER and available for use at the laboratory. The seismic configuration on the COLMEIA cruise used 24 hydrophones and 2airguns. The value of 1500 m/s was assigned for the velocity of the sound wave on the water and sediments. After processing, interpretation was performed using a specific software called Kingdom 8.5. During the first part of the interpretation, the focus was to identify the most important seismic horizons, such as the basement and major seismic horizons inside the sediment infill. The seismic profiles showed a strongly rugged bathymetry. One can easily note that the area is full of geological depressions, representing fracture zones, forming small, elongated basins. These features, that during millions of years gathered sediments, most of them hemipelagic and volcanogenic, allow to infer the age of each sector of the study area and shows some deformation at their upper part. Some difficulties were faced, due to the strongly rugged bathymetry in the area, during the interpretation of the seismic profiles. Thus, some seismic attributes were used to find where is the true ocean floor. One method used was the envelope, since this seismic attribute represents the instantaneous energy of the signal and its magnitude is proportional to the reflection coefficient.
Logging data are measurements of physical properties of the formation surrounding a borehole, acq... more Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.
Images of the outside of hard rock whole-round sections were acquired using a linescan imager (Se... more Images of the outside of hard rock whole-round sections were acquired using a linescan imager (Section Half Imaging Logger [SHIL]) and a special holder that allows each 90 degree segment of the outer surface to be positioned properly. The images were taken at a resolution of 20 lines/mm (50 micropixels). JRSO staff take these quadrant images and compile them into a side-by-side \rollout\ photograph of the section. Composite images are available as both JPG and TIF image formats. Individual quadrant images are available as JPG images only through this report; contact the IODP-JRSO Data Librarian if quadrant TIF files (~160 MB) are needed.
The George V and Tasman Transform Fault Systems (TFS) are major, right-stepping offsets of the So... more 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 s...
We studied the east intersection between the Romanche transform fault (TF) and the Mid-Atlantic r... more We studied the east intersection between the Romanche transform fault (TF) and the Mid-Atlantic ridge using bathymetry and gravity anomalies, to investigate the temporal evolution of the ultra-cold ridge-transform intersection. Our results reveal a complex ridge axis, with evidence of a significant decrease in the along-axis melt supply towards the RTI but also since ~10 Ma.Over a 100 km distance south of the RTI, the ridge axis is formed by three spreading segments offset by large non-transform discontinuities. Large detachment faults mark the present-day spreading style at the RTI, while magma supply increases away from the Romanche intersection. Axial and near-axis fault patterns reveal a marked obliquity, especially in the north and center of the study area.In lithosphere older than 10 Ma, the ridge axis appears to form a single spreading segment between the Romanche and Chain TFs, perpendicular to the spreading direction, with relatively regular abyssal hills. From around 10 to...
At mid-oceanic ridges, mantle temperature and magma supply influence the structure of the neo-vol... more At mid-oceanic ridges, mantle temperature and magma supply influence the structure of the neo-volcanic zone. Due to the large Romanche offset, a strong “cold edge” effect is present at its eastern intersection with the Mid-Atlantic Ridge. This effect decreases with the distance from the transform fault, making this region an ideal area to study the impact of the thermal gradient on the architecture of the neo-volcanic zone. We analyzed seafloor videos and photos from submersible dives, as well as bathymetry and backscatter data collected during the SMARTIES cruise (2019), from the Ridge-Transform Intersection (RTI) to approximately 80 km to the south of it. We produced maps at local and regional scales and quantified the morphology of volcanoes (height, diameter, height/diameter ratio, volume and surface). Visual observations have showed that the seafloor is mainly made up of pillows or elongated pillows and rare massive lava flows. Within 30 km of the RTI, the neo-volcanic area is ...
We present data for glassy basalts from ~37 localities along the spreading axis of the Southeast ... more We present data for glassy basalts from ~37 localities along the spreading axis of the Southeast Indian Ridge (SEIR) between 126\ub0-140\ub0E, eastward of the Australian-Antarctic Discordance (AAD). Each of the five ridge segments (A1 to A5, west to east) show well-defined major element trends. An isotopic and negative axial depth anomaly is present, centered on the overlapping tips of segments A3 and A4 at ~135\ub0E. Segment A4 basalts have distinct radiogenic Pb and He isotopes plus enriched MORB-like \u3b5Hf, relative to segments to the west and east. Crystal fractionation is more extensive at the A3 and A5 overlapping segment tips adjacent to A4, and decreases both to the west and east. The along axis pattern suggests a mantle heterogeneity located beneath the A3-A4 segments. Pb-Pb isotopic co-variations for the 5 segments define two linear arrays, with a western trend (A1-A3) and an eastern trend (A4-A5) that intersects it at the composition of the anomalous A4 segment, at a 206Pb/204Pb ~ 19. The western trend has higher 208Pb/204Pb for a given 206Pb/204Pb, revealing a gradient in the asthenosphere, with 06208Pb/204Pb decreasing to the east away from the AAD. Overall, 206,207,208Pb/204Pb and 4He/3He of the A4 anomaly define trends that vector toward the fields for Cenozoic lavas from west Antarctica (Marie Byrd Land and Balleny Islands). West Antarctica has a history of mantle plume underplating and lithosphere modification by subduction [1,2], and there is a broad seismic anomaly below 250 km underlying the West Antarctic Rift system [3]. Our data supports a model in which flow of underplated material plus lithosphere may be guided by the underside topography of the lithosphere beneath the Transantarctic mountains. This flow emerges from beneath east Antarctica, where it leads to volcanism in the Balleny Islands [4]. The material apparently continues to flow northward to the SEIR at ~135\ub0E. The geochemical anomaly beneath Zone A is potentially explained by the presence of this residual plume/mobilized lithospheric material in the subridge mantle of the SEIR. [1] Hart et al., 1997, Chem Geol 139; [2] Aviado et al. 2015, G3 16; [3] Moelli and Danesi, 2004, GPC 42; [4] Sleep, 2006, ESR 77
Oceanic crust is formed by melt derived from the mantle at oceanic spreading centers. A small amo... more Oceanic crust is formed by melt derived from the mantle at oceanic spreading centers. A small amount of melting initiates at about 150-300 km depths in the presence of volatiles (CO2, H2O)1–3, but the extensive dry melting commences at 60-70 km depths due to the upwelling of the mantle as two diverging plates move apart4,5. However, how these melts migrate to the surface and what happens to these melts in the upper part of the mantle are still not understood. Using seismological data recorded by ocean-bottom seismometers, here we report the presence of deep earthquakes at 10-20 km depth in the hot mantle along the Mid-Atlantic Ridge axis, much below the brittle-ductile boundary, suggesting that these earthquakes are caused by a volume change associated with the CO2 degassing from the ascending melt. The geochemical analyses of basalts from the ridge axis show an abnormally high quantity of CO2 (>1.9 wt%) in the primitive melt, confirming the CO2 degassing hypothesis. The large co...
2015 IEEE/OES Acoustics in Underwater Geosciences Symposium (RIO Acoustics), 2015
The COLMEIA Project is an international collaboration between France and Brazil involving several... more The COLMEIA Project is an international collaboration between France and Brazil involving several universities and research institutes. One of the objectives of this project is to study the tectonic evolution and to understand the processes that result in the exhumation of the ultramafic body which composes the São Pedro e São Paulo archipelago, as wellasthe magmatism and tectonics of this part of the Mid-Atlantic Ridge, especially for the recent geologic time. The work is essential to understand the evolution of the Equatorial Atlantic Ocean. A fundamental part of thestudy targets the detailed analysis of sites that indicate recent off-axis deformation, since these faults could work as pathways for hydrothermal fluids, which is important to understand hydrothermalism in sediment environments. This paper presents the preliminary results of the analysis of the seismic data acquired during the COLMEIA cruise. The first step was to process the seismic lines in the north part of the area covered during the cruise, where the St. Peter peridotite ridge is located. The software used, Sispeed v5.5, was developed by the IFREMER and available for use at the laboratory. The seismic configuration on the COLMEIA cruise used 24 hydrophones and 2airguns. The value of 1500 m/s was assigned for the velocity of the sound wave on the water and sediments. After processing, interpretation was performed using a specific software called Kingdom 8.5. During the first part of the interpretation, the focus was to identify the most important seismic horizons, such as the basement and major seismic horizons inside the sediment infill. The seismic profiles showed a strongly rugged bathymetry. One can easily note that the area is full of geological depressions, representing fracture zones, forming small, elongated basins. These features, that during millions of years gathered sediments, most of them hemipelagic and volcanogenic, allow to infer the age of each sector of the study area and shows some deformation at their upper part. Some difficulties were faced, due to the strongly rugged bathymetry in the area, during the interpretation of the seismic profiles. Thus, some seismic attributes were used to find where is the true ocean floor. One method used was the envelope, since this seismic attribute represents the instantaneous energy of the signal and its magnitude is proportional to the reflection coefficient.
Logging data are measurements of physical properties of the formation surrounding a borehole, acq... more Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.
Images of the outside of hard rock whole-round sections were acquired using a linescan imager (Se... more Images of the outside of hard rock whole-round sections were acquired using a linescan imager (Section Half Imaging Logger [SHIL]) and a special holder that allows each 90 degree segment of the outer surface to be positioned properly. The images were taken at a resolution of 20 lines/mm (50 micropixels). JRSO staff take these quadrant images and compile them into a side-by-side \rollout\ photograph of the section. Composite images are available as both JPG and TIF image formats. Individual quadrant images are available as JPG images only through this report; contact the IODP-JRSO Data Librarian if quadrant TIF files (~160 MB) are needed.
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Papers by Anne Briais