Anne Briais

Université de Bretagne Occidentale | UBO · Institut Universitaire Européen de la Mer (IUEM)

Accretionary processes at mid‐ocean ridge segments with low magma input have seldom been investigated over the long term. The evolution of such magma‐starved segments over time is still largely unknown. We present a study on the structure and evolution of the southernmost intra‐transform ridge segment of the St. Paul Transform Fault System in the E...

Following the India￣Asia collision, continental blocks were extruded along large sinistral strike￣slip faults. The longest such fault, the Ailao Shan￣Red River shear zone (ASRR), separated Indochina (Sundaland) from South China. The ~ 1000 km￣long, active Red River fault (RRF) extends along the north side of the Ailao Shan and currently exhibits a...

Following the India-Asia collision, continental blocks were extruded along large sinistral strike-slip faults. The longest such fault, the Ailao Shan - Red River shear zone (ASRR), separated Indochina (Sundaland) from South China. The ~1000 km-long, active Red River fault (RRF) extends along the north side of the Ailao Shan and currently exhibits a...

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...

Continental breakup represents the successful process of rifting and thinning of the continental lithosphere, leading to plate rupture and initiation of oceanic crust formation. Magmatism during breakup seems to follow a path of either excessive, transient magmatism (magma-rich margins) or of igneous starvation (magma-poor margins). The latter type...

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...

Mantle exhumation at slow-spreading ridges is favoured by extensional tectonics through low-angle detachment faults, and, along transforms, by transtension due to changes in ridge/transform geometry. Less common, exhumation by compressive stresses has been proposed for the large-offset transforms of the equatorial Atlantic. Here we show, using high...

Anne Briais (1) and the IODP Expedition 349 Scientists (2) Team (1) CNRS Geosciences Environment Toulouse, France (anne.briais@cnrs.fr), (2) iodp.tamu.edu/scienceops/precruise/southchinasea/participants.html The International Ocean Discovery Program (IODP) Expedition 349 in the South China Sea drilled three sites (U1431, U1433, and U1434) into the...

We present observations of the SouthEast Indian Ridge (SEIR) collected during the STORM cruise (South Tas-mania Ocean Ridge and Mantle) on the N/O L'Atalante early 2015. The SEIR between Australia and Antarctica displays large variations of axial morphology despite an almost constant intermediate spreading rate. The Australia-Antarctic Discordance...

Preliminary report of the COLMEIA cruise along the St. Paul Fracture Zone System, Equtorial Atlantic. FROM INTERRIDGE NEWS 2013/2014 - VOLUME 22 http://www.interridge.org/

Newly discovered hydrothermal plumes along the Furious Fifties, South East Indian Ridge (SEIR; 128°E-140°E)

The current interpretation of the Messinian Salinity Crisis (MSC) involves the deposition of peripheral or marginal evaporites in onshore basins as well as the erosion of the margin and the deposition of thick evaporites in deep basins. The so-called intermediate basins are formed in domains between the onland outcrops and the deep basins. The Bale...

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 Sao Pedro e Sao Paulo archipelago, as...

Two major types of kinematic models have been proposed to explain the opening of the western Mediterranean basins (Liguro-Provençal and Algerian basins, and Valencia trough). In one type of models, all continental blocks bounding the basins drift to the southeast, driven by the rollback of the Tethys subduction slab. In the other type of models, th...

The Béarn range, located to the north of the Axial Zone in the Western Pyrenees, is affected by numerous small-magnitude seismic events. These events overlap an area characterized by specific geological structures which are interpreted to have resulted from multistage extensional and compressional deformation. An analysis of surface geology draped...

Coring/logging data and physical property measurements from International Ocean Discovery Program Expedition 349 are integrated with, and correlated to, reflection seismic data to map seismic sequence boundaries and facies of the central basin and neighboring regions of the South China Sea. First-order sequence boundaries are interpreted, which are...

Combined analyses of deep tow magnetic anomalies and International Ocean Discovery Program Expedition 349 cores show that initial seafloor spreading started around 33 Ma in the northeastern South China Sea (SCS), but varied slightly by 1–2 Myr along the northern continent-ocean boundary (COB). A southward ridge jump of ∼20 km occurred around 23.6 M...

Multiple geological processes affect the distribution of hydrothermal venting along a mid-ocean ridge. Deciphering the role of a specific process is often frustrated by simultaneous changes in other influences. Here we take advantage of the almost constant spreading rate (65-71 mm/yr) along 2500 km of the Southeast Indian Ridge (SEIR) between 77°-9...

The South China Sea (SCS) provides an outstanding opportunity to better understand complex patterns of continental margin breakup and basin formation. The sea is situated at the junction of the Eurasian, Pacific, and Indo-Australian plates and is a critical site linking some of the major western Pacific tectonic units. Despite extensive studies, sa...

We present here a set of digital maps of the Earth's gravity anomalies (surface free air, Bouguer and isostatic), computed at Bureau Gravimetric International (BGI) as a contribution to the Global Geodetic Observing Systems (GGOS) and to the global geophysical maps published by the Commission for the Geological Map of the World (CGMW) with support...

World Gravity Map (WGM) denotes a set of 3 global anomaly maps of the Earth’s gravity field realized by the Bureau Gravimétrique International (BGI), a service of the International Association of Geodesy (IAG). These new products, realized for the Commission for the Geological Map of the World (CGMW), UNESCO, International Union of Geodesy and Geop...

We present here a set of digital maps of the Earth's gravity anomalies (surface "free air", Bouguer and isostatic), computed at Bureau Gravimetric International (BGI) as a contribution to the Global Geodetic Observing Systems (GGOS) and to the global geophysical maps published by the Commission for the Geological Map of the World (CGMW). The free a...

The availability of high-resolution global digital elevation data sets has raised a growing interest in the feasibility of obtaining their spherical harmonic representation at matching resolution, and from there in the modelling of induced gravity perturbations. We have therefore estimated spherical Bouguer and Airy isostatic anomalies whose spheri...

Temporal fluctuations of magmatic processes during the last 800 kyr have been investigated for the slow spreading Central Indian Ridge. The fluctuations are recorded by variations in lava chemistry along a 40 km long profile across the ridge. The temporal relations of the basalts were accurately restored using magnetic microanomalies. We report on...

The WGM project is a gravity mapping project undertaken under the aegis of the Commission for the Geological Map of the World (CGMW) to complement a set of global geological and geophysical digital maps published and updated by CGMW, such as the World Digital Magnetic Anomaly Map (WDMAM), released in 2007. This new global digital map aims to provid...

Non–hot spot, intraplate volcanism is a common feature near the East Pacific Rise or Pacific-Antarctic ridge. Volcanic ridges and seamount chains, tens to hundreds of kilometers long, are asymmetrically distributed about the ridge axis, with most volcanic features occurring on the Pacific plate. Their origins remain controversial. We have analyzed...

Lebanon, located on a 160-km-long transpressional bend of the left-lateral Levant (Dead Sea) fault system (LFS), has been the site of infrequent but large earthquakes, including one submarine, tsunamigenic event. The main objective of the Shalimar marine survey was to characterize and map active deformation offshore of Lebanon using a range of geop...

The intermediate-spreading Southeast Indian Ridge (SEIR) between Australia and Antarctica is mostly known for the presence of the Australia-Antarctic Discordance, an area of low magma budget on the ridge. Here we focus on the area east of the discordance, where we have analyzed gravity highs observed on satellite-derived maps of the flanks of the S...

We propose to document the timescale of the magmatic processes occurring beneath the slow-spreading Central Indian Ridge (CIR, 19°2S) through the study of the chemical variations recorded by lavas erupted on-axis. The samples have been collected along a 40 km-long profile transverse to the ridge and running from the ridge axial through up to the Br...

[1] We investigated the morphology and structure of the Pacific-Antarctic Ridge between 52°45′S and 41°15′S during the Pacantarctic2 cruise using multibeam echosounder together with gravity measurements and dredges. Analysis of the bathymetric, gravity and geochemical data reveal three ridge segments separated by overlapping spreading centers south...

We present the analysis of the deformation in the axial valley of two contrasted regions of the very slow spreading Southwest Indian Ridge based on side-scan sonar images. Our objective is to investigate how the obliquity is accommodated along the system. We show that the robust magmatic segments have axial valleys and major faults subperpendicular...

During the Pacantarctic 2 cruise of the R/V L'Atalante in December 2004 and January 2005, we mapped and dredged large off-axis volcanic structures on the flanks of the Pacific-Antarctic ridge: two ridges on either side of the Menard transform fault (TF) near 50°S, and E-W-trending ridges near 42°S. One objective of the cruise was to understand how...

During the PACANTARCTIC 2 cruise, from December 17, 2004 to January 17, 2005, onboard the French research vessel L'Atalante, the geomorphology of the Pacific-Antarctic Ridge was mapped using EM12 multibeam bathymetry and imagery between 53° and 41° S together with along axis gravity measurements and dredges. The ridge axis generally deepens in this...

The objectives of the SHALIMAR cruise were to study recent deformation of the Mediterranean seafloor west of Mt Lebanon. We collected multibeam bathymetry and back-scatter images, reflection seismic profiles - surface and deep-towed, 3.5 kHz echo-sounder data, gravity and magnetic data over an 80 km-wide zone offshore the entire Lebanese coast. The...

On July 9, AD 551, a large earthquake, followed by a tsunami destroyed most of the coastal cities of Phoenicia (modern-day Lebanon). This was arguably one of the most devastating historical submarine earthquakes in the eastern Mediterranean. Geophysical data from the Shalimar survey unveils the source of this Mw=7.5 event: rupture of the offshore,...

The M>7 earthquake that struck the shore of Lebanon in 551 AD was associated with a large tsunami that destroyed Beyrouth and other seaports, and thus likely originated offshore. Onshore in the north, the Tripoli thrust, whose 70m-high cumulative scarp cuts the city in half, is responsible for the Plio-Quaternary growth and current uplift of the Tu...

The dense grid of 6-channel seismic profiles, complemented by 25 high-resolution profiles, shot offshore Lebanon during the SHALIMAR cruise provides exceptional insight into the stratigraphy of the top 3.5 km of sediments, and into the evolution of Miocene to Quaternary tectonic deformation. The topmost sediments are Plio-Quaternary turbidites, rea...

We use gravity anomalies along the conjugate passive margins of Australia and Antarctica to investigate the segmentation of these margins and the signature of the Australia-Antarctica Discordance (AAD). We estimated the residual isostatic anomaly (RIA) along both margins to characterize the longitudinal variations of the margin crustal structure at...

The aim of our analysis is to assess the role of mantle temperature anomalies in the structure of continental margins. We analyze the longitudinal variations of the crustal structure of the southern Atlantic continental margins to investigate the segmented character of the margins and the impact of the hotspots at the time of opening. We use free-a...

New deep tow sidescan sonar data from the Southwest Indian Ridge reveal complex volcanic/tectonic interrelationships in the axial zone of this ultra-slow spreading ridge. While some constructional volcanic features resemble examples documented at the slow-spreading Mid-Atlantic Ridge, such as axial volcanic ridges, hummocky and smooth lava flows, t...

We present three-dimensional numerical models of convection within the partially molten mantle beneath the ridge axis. The modeling takes into account the cavity flow driven by plate spreading, the diffuse upwelling due to plate accretion, and the shearing movement generated by large-scale mantle flow. The ridge axis is free to move in the spreadin...

We analyze the structure and evolution of two propagators along the Pacific–Antarctic Ridge (PAR) that we surveyed during the Pacantarctic cruise of the N/O L’Atalante. A large propagator at 63°30′S, 167°W shows a N50°E-trending segment of the PAR propagating southwestward, while the adjacent, N45°E-trending segment retreats. The propagating and do...

New deep tow sidescan sonar data from the Southwest Indian Ridge reveal complex volcanic/tectonic interrelationships in the axial zone of this ultra-slow spreading ridge. While some constructional volcanic features resemble examples documented at the slow-spreading Mid-Atlantic Ridge, such as axial volcanic ridges, hummocky and smooth lava flows, t...

The high-resolution geoid and gravity maps derived from ERS-1 and Geosat satellite geodetic missions reveal a set of small-scale lineations on the flanks of slow to intermediate spreading mid-ocean ridges. Assuming that these lineations reflect the variations in crustal structure induced by mid-ocean ridge axial discontinuities, we use them to inve...

We present an analysis of multibeam bathymetry, backscatter imagery, and gravity data collected during the Magofond2 and Gimnaut cruises, and of satellite-derived gravity anomalies, on the flanks of the Central Indian Ridge (CIR). The bathymetry data reveal that the CIR axis near 19\deg S is about 1000 m shallower than normal, slow-spreading ridge...

Bathymetric, gravity, magnetic and backscattering strength data have been used to characterise the segmentation of an 800 km long portion of the ultraslow-spreading Southwest Indian Ridge (SWIR, full rate 14 mm/yr) between 49°15′E and 57°E. This analysis reveals that the segmentation defined by along-axis variations of depth and by occurrence of ax...

The spreading rate at the Pacific-Antarctic Ridge (PAR) increases rapidly from 54 mm/yr near Pitman Fracture Zone (FZ) up to 76 mm/yr near Udintsev FZ, resulting in three domains of axial morphology: an axial valley south of Pitman FZ, an axial high north of Saint Exupery FZ, and in between, the transitional domain extends over 650 km. It comprises...

The Rodrigues Ridge is an E-W volcanic structure which extends at 19° S from the Mascarene Plateau (59° 30'E) to 100 km East of Rodrigues Island (64° 30'E). It is neither parallel to seafloor spreading flow-lines nor to the "absolute" motion of Africa in the hotspot reference frame. 39Ar-40Ar dating of dredged samples has shown that the whole ridge...

We used satellite-derived gravity anomaly maps and bathymetry data to analyze the distribution of off-axis seamounts on young crust on the flanks of the East Pacific Rise (EPR) and northern Pacific–Antarctic Ridge (PAR), from 17°N to 56°S latitude. We observed large-scale variations in the distribution of the volcanoes which we attribute to variati...

We analyse TOBI side-scan sonar images collected during Charles Darwin cruise CD76 in the axial valley of the Mid-Atlantic Ridge (MAR) between 27N and 30N (Atlantis Transform Fault). Mosaics of the two side-scan sonar swaths provide a continuous image of the axial valley and the inner valley walls along more than six second-order segments of the MA...

A recent survey of the Mid-Atlantic Ridge over the southern edge of the Azores Platform shows that two anomalously shallow regions located off-axis on both sides of the ridge are the two flanks of a single rifted volcanic plateau. Crustal thickness over this plateau is up to twice that of surrounding oceanic areas, and original axial depths were ne...

Because of the proximity of the Euler poles of rotation of the Pacific and Antarctic plates, small variations in plate kinematics are fully recorded in the axial morphology and in the geometry of the Pacific-Antarctic Ridge south of the Udintsev fracture zone. Swath bathymetry and magnetic data show that clockwise rotations of the relative motion b...

The morphological characteristics of the segmentation of the Central Indian Ridge (CIR) from the Indian Ocean Triple Junction (25°30'S) to the Egeria Transform Fault system (20°30'S) are analyzed. The compilation of Sea Beam data from R/VSonne cruises SO43 and SO52, and R/VCharcot cruises Rodriguez 1 and 2 provides an almost continuous bathymetric...

THE small-scale segmentation of mid-ocean ridges with an axial rise has been modelled by considering each ridge segment as a giant crack in the lithosphere with a tip propagating along the ridge axis1,2. For ridges with an axial valley, however, this type of model fails because the lithosphere is too thick to tear3. Yet such ridges are clearly segm...

The segmentation of the Mid-Atlantic Ridge between 29°N and 31°30′ N during the last 10 Ma was studied. Within our survey area the spreading center is segmented at a scale of 25–100 km by non-transform discontinuities and by the 70 km offset Atlantis Transform. The morphology of the spreading center differs north and south of the Atlantis Transform...

A survey along the axis of the slow-spreading Mid-Atlantic Ridge, between 27°N and 30°N, using a combination of geophysical imaging and geochemical sensing has assessed the regional extent of hydrothermal activity. As a result, three areas were identified as possible sources of hydrothermal activity: at 27°00′N, 29°10′N and 30°02′N. The location of...

An updated interpretation of the magnetic data of the South China Sea is presented, and its implications for the evolution of the South China Sea spreading ridge are discussed. A new identification of magnetic lineations in the basin is described. The kinematic parameters of spreading are then computed from the fit of the magnetic isochrons, and th...

The present morphology and tectonic evolution of more than 1500 kilometres of the Central Indian Ridge are described and discussed following the integration of GLORIA side-scan sonographs with conventional geophysical datasets. Segmentation of the ridge occurs by a series of ridge axis discontinuities ranging in periodicity along strike from 275 km...

In order to access seismic hazard in the eastern Pyrenees and northern Catalonia, we analyse the tectonics and Quaternary morphology of the area, as revealed by satellite images, aerial photos, topographic maps and fieldwork. We conclude that several normal faults, such as the Capcir, Conflent-Cerdaña and Tech fault systems, which are generally ori...

The South China Sea is a mid-late Tertiary marginal basin. The magnetic anomaly lineations in the eastern part of the basin trend approximately east-west [1,2], suggesting a north-south direction of spreading. In the spring of 1985, two cruises on the French research vessel ``Jean Charcot'' provided Sea Beam coverage, seismic reflection, magnetic a...

Recent work1,2 indicates that the South China Sea is an `Atlantictype' marginal basin of late Tertiary age. Magnetic anomalies in the eastern part of the sea are consistent with seafloor spreading directed approximately north-south1,2. We present here a new morphostructural study based on coupled seabeam mapping and single-channel seismic reflectio...