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Hydrothermal eruptions are characterised by violent explosions ejecting steam, water, mud, and rock. They pose a risk to tourism and the operation of power plants in geothermal areas around the world. Large events with a severe destructive threat are often intensified by the injection of magmatic fluids along faults and fractures within volcano-tectonic rifting environments, such as the Taupo Volcanic Zone. How these hydrothermal eruptions progress, how craters form and the scale of ejecta impacts, are all influenced by the local geology and reservoir hydrology. By analysing breccia lithology, undisturbed strata proximal to the explosion sites, and conducting tailored decompression experiments, we elucidate the eruption sequence that formed Champagne Pool, Wai-o-tapu, New Zealand. This iconic touristic site was formed by a violent hydrothermal eruption at ~ 700 years B.P. Samples from undisturbed drill cores and blocks ejected in the eruption were fragmented in shock-tube experiments under the moderate pressure/temperature conditions estimated for this system (3–4 MPa, 210–220 °C). Our results show that this was a two-phase eruption. It started with an initial narrow jetting of deep-sourced lithologies, ejecting fragments from at least a 110-m depth. This event was overtaken by a larger, broader, and dominantly shallower eruption driven by decompression of much more geothermal fluid within a soft and porous ignimbrite horizon. The second phase was triggered once the initial, deeper-sourced eruption broke through a strong silicified aquitard cap. The soft ignimbrite collapsed during the second-phase eruption into the crater, to repeatedly choke the explosions causing short-term pressure rises that triggered ongoing deeper-sourced eruptions. The eruption spread laterally also by exploiting a local fault. These results are relevant for hydrothermal eruption hazard scenarios in environments where strong vertical variations in rock strength and porosity occur., Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659, Ministry of Business, Innovation and Employment http://dx.doi.org/10.13039/501100003524

International audience; The drive towards improving tsunami risk mitigation has intensified along many populated coastlines. Like many islands in the Pacific Ocean, the coastal population of New Caledonia is exposed to tsunamis triggered by powerful earthquakes. Intersecting exhaustive population data with high-resolution building location data within a user-defined coastal fringe is an accurate means of geolocating vulnerable residents, and an important step towards disaster risk reduction. This paper presents a mixed methodology built on GIS-based dasymetric techniques for assessing, classifying, and mapping population distribution in New Caledonia, with the aim of quantifying and ranking the areas most vulnerable to tsunami-related hazards. Results reveal that 33% of the population, inclusive of previously unmapped precarious housing, lives between sea level and the 10 m elevation contour in well-defined clusters. A pilot field survey of 412 respondents was additionally conducted in the capital Nouméa (66% of the nation's population) to assess tsunami awareness, risk perception, and risk-related behavioral patterns among the ethnically and demographically diverse population. By further mapping the spatial association between coastal population concentrations, the perceived natural shielding capacities of coral reefs and mangroves, and the benefits of alarm siren networks, the study delivers a comprehensive assessment of the country's disaster preparedness, with policy recommendations for the future. The methodology is transferable to other types of hazards and other insular settings where civil security and risk-management organizations acquire and curate reliable primary data but may also need guidelines for transforming them into serviceable disaster risk reduction methods and policies.

Vrancea, Eastern Romania, presents a significant intermediate-depth seismicity, between 60 and 170 km depth, i.e. pressures from 2 to 6.5 GPa. A debate has been lasting for decades regarding the nature of the seismic volume, which could correspond to the remnant of a subducted slab of Tethyan lithosphere or a delamination of the Carpathians lithosphere. Here we compile the entire seismicity dataset (≈ 10,000 events with 2 ≤ Mw ≤ 7.9) beneath Vrancea for P > 0.55 GPa (> 20 km) since 1940 and estimate the pressure and temperature associated with each hypocenter. We infer the pressure and temperature, respectively, from a depth-pressure conversion and from the most recent tomography-based thermal model. Pressure–temperature diagrams show to what extent these hypocentral conditions match the thermodynamic stability limits for minerals typical of the uppermost mantle, oceanic crust and lower continental crust. The stability limits of lawsonite, chloritoid, serpentine and talc minerals show particularly good correlations. Overall, the destabilization of both mantle and crustal minerals could participate in explaining the observed seismicity, but mantle minerals appear more likely with more convincing correlations. Most hypocentral conditions match relatively well antigorite dehydration between 2 and 4.5 GPa; at higher pressures, the dehydration of the 10-Å phase provides the best fit. We demonstrate that the Vrancea intermediate-depth seismicity is evidence of the current dehydration of an oceanic slab beneath Romania. Our results are consistent with a recent rollback of a W-dipping oceanic slab, whose current location is explained by limited delamination of the continental Moesian lithosphere between the Tethyan suture zone and Vrancea.

We present new Sr, Nd, Hf and Pb isotope data for Early Miocene shoshonitic and high-K lavas dredged from seamounts in the South Fiji Basin, southwest Pacific Ocean. Our analyses provide a useful r...

The data that support the findings of this study are openly available in figshare at: https://figshare.com/articles/journal_contribution/Claussmann_et_al_NZJGG_Supplementary_material/13614101; International audience; Continental shelves generally supply large-scale mass-wasting events. Yet, the origin and significance of shelf-derived mass-transport deposits (MTDs) for the tectonostratigraphic evolution of subduction complexes and their trench-slope basins have not been extensively studied. Here, we present high-resolution, outcrop-scale insights on both the nature of the reworked sediments, and their mechanisms of development and emplacement along tectonically active margins, by examining the Middle Miocene shelf-derived MTDs outcropping in the exhumed southern portion of the Hikurangi subduction margin. Results show that periods of repeated tectonic activity (thrust propagation, uplift) in such compressional settings not only affect and control the development of shelfal environments but also drive the recurrent generation and destruction of oversteepened slopes, which in turn, favour the destabilisation and collapses of the shelves and their substratum. Here, these events produced both large-scale, shelf-derived sediment mass-failures and local debris flows, which eventually broke down into a series of coalescing, erosive, genetically linked surging flows downslope. The associated MTDs have a regional footprint, being deposited across several trench-slope basins. Recognition of tectonic activity as another causal mechanism for large-scale shelf failure (in addition to sea-level changes, high-sedimentation fluxes) has implications for both stratigraphic predictions and understanding the tectonostratigraphic evolution of deep-marine fold-and-thrust belts.

International audience; Past shallow-water carbonate environments of the main island of New Caledonia (NC) have been subject to high terrigenous influx derived from the erosion of ultramafic obducted nappes and are therefore a relevant case study for characterizing neritic carbonate production in mixed carbonate-siliciclastic systems under a tropical climate. More particularly, we focused on Burdigalian carbonate sedimentary records cropping out on the western coast of NC, in the Nepoui area. Based on a comprehensive sedimentological study of cores and outcrops, we established a new depositional model of an alluvial fan to carbonate ramp transition. Shallow-water (euphotic) carbonate production was dominated by seagrass-related biota and corals derived from small-sized bioconstructions. Extensional tectonics and associated normal faulting, driven by post-obduction isostatic rebound, favored carbonate ramp aggradation and preservation. The carbonate ramp was incised by conglomerate-filled terminal distributary channels, which indicate that terrigenous inputs remained significant during marine transgression and did not inhibit the development of seagrass and scleractinian carbonate factories. Phytal substrates induced by seagrass and/or macro-algae seafloor colonization strongly controlled the nature of carbonate production and promoted the accumulation of foraminiferal-coralline algal sediments. Seagrass development at the front of the fan delta is interpreted to have controlled the preservation of a diverse and significant carbonate production by reducing water turbidity and by limiting the risk of suffocation for filter-feeding biota in such a high terrigenous influx setting.

Displacement waveforms derived from Global Navigation Satellite System (GNSS) data have become more commonly used by seismologists in the past 15 yrs. Unlike strong‐motion accelerometer recordings that are affected by baseline offsets during very strong shaking, GNSS data record displacement with fidelity down to 0 Hz. Unfortunately, fully processed GNSS waveform data are still scarce because of limited public availability and the highly technical nature of GNSS processing. In an effort to further the use and adoption of high‐rate (HR) GNSS for earthquake seismology, ground‐motion studies, and structural monitoring applications, we describe and make available a database of fully curated HR‐GNSS displacement waveforms for significant earthquakes. We include data from HR‐GNSS networks at near‐source to regional distances (1–1000 km) for 29 earthquakes between Mw 6.0 and 9.0 worldwide. As a demonstration of the utility of this dataset, we model the magnitude scaling properties of peak ground displacements (PGDs) for these events. In addition to tripling the number of earthquakes used in previous PGD scaling studies, the number of data points over a range of distances and magnitudes is dramatically increased. The data are made available as a compressed archive with the article. The authors thank Ronni Grapenthin and Valerie Sahakian for helpful discussions on the peak ground displacement (PGD) scaling law and residuals. This work was funded by the Gordon and Betty Moore Foundation through Grant GBMF3024 to University of California (UC) Berkeley and the U.S. Geological Survey Grants G16AC00348 and G17AC00346 to UC Berkeley. Work was also done under Grant 41674033 from the National Science Foundation of China. Scripps Orbit and Permanent Array Center (SOPAC) work was funded by NASA Grants NNH17ZDA001N, NNX16AM04A and NNX17AD99G and National Science Foundation (NSF) Grant EAR-1400. The authors thank the Geospatial Information Authority of Japan for operation and maintenance of the GEONET Global Positioning System (GPS) network whose data are used in this study. The authors gratefully acknowledge all the personnel from Servicio Sismologico Nacional (SSN), Servicio de Geodesia Satelital (SGS) and UNAVCO Inc. for GPS station maintenance, data acquisition, IT support and data distribution. The authors acknowledge the New Zealand GeoNet project and its sponsors EQC, GNS Science, and LINZ, for providing data used in this study.

J. Shao and L.D. Stott were supported by an NSF grant (MG&G 1558990). W. R. Gray and R. Greenop were supported by NERC grants NE/N011716/1 and NE/N011716/1 to J.W.B. Rae. I. Pecher, H.L. Neil, and B. Davy were supported by RSNZ Marsden Fund grant UOA1022. R. Coffin was supported by a DOE-NETL contract to NRL subcontract to TAMUCC (#601970). Identifying processes within the Earth System that have modulated atmospheric pCO2 during each glacial cycle of the late Pleistocene stands as one of the grand challenges in climate science. The growing array of surface ocean pH estimates from the boron isotope proxy across the last glacial termination may reveal regions of the ocean that influenced the timing and magnitude of pCO2 rise. Here we present two new boron isotope records from the subtropical‐subpolar transition zone of the Southwest Pacific that span the last 20 kyr, as well as new radiocarbon data from the same cores. The new data suggest this region was a source of carbon to the atmosphere rather than a moderate sink as it is today. Significantly higher outgassing is observed between ~16.5‐14 kyrBP, associated with increasing δ13C and [CO3]2‐ at depth, suggesting loss of carbon from the intermediate ocean to the atmosphere. We use these new boron isotope records together with existing records to build a composite pH/pCO2 curve for the surface oceans. pH disequilibrium/CO2 outgassing was widespread throughout the last deglaciation, likely explained by upwelling of CO2 from the deep/intermediate ocean. During the Holocene, a smaller outgassing peak is observed at a time of relatively stable atmospheric CO2, which may be explained by regrowth of the terrestrial biosphere countering ocean CO2 release. Our stack is likely biased toward upwelling/CO2 source regions. Nevertheless, the composite pCO2 curve provides robust evidence that various parts of the ocean were releasing CO2 to the atmosphere over the last 25 kyr. Publisher PDF

International audience; Earthquakes start under conditions that are largely unknown. In laboratory analogue experiments and continuum models, earthquakes transition from slow-slipping, growing nucleation to fast-slipping rupture. In nature, earthquakes generally start abruptly, with no evidence for a nucleation process. Here we report evidence from a strike-slip fault zone in central Alaska of extended earthquake nucleation and of very-low-frequency earthquakes (VLFEs), a phenomenon previously reported only in subduction zone environments. In 2016, a VLFE transitioned into an earthquake of magnitude 3.7 and was preceded by a 12-hour-long accelerating foreshock sequence. Benefiting from 12 seismic stations deployed within 30 km of the epicentre, we identify coincident radiation of distinct high-frequency and low-frequency waves during 22 s of nucleation. The power-law temporal growth of the nucleation signal is quantitatively predicted by a model in which high-frequency waves are radiated from the vicinity of an expanding slow slip front. The observations reveal the continuity and complexity of slip processes near the bottom of the seismogenic zone of a strike-slip fault system in central Alaska.

Amber is nearly ubiquitous in lignites from Otago and Southland and cornmon throughout New Zealand; however, no amber inclusions have been reported previously. We studied amber from 22 Cretaceous to Miocene sites in southem New Zealand, recovering inclusions at three localities: Cosy Dell (late Oligocene), Roxburgh (early Miocene), and Hyde (?early Miocene). Preparation of New Zealand amber to expose inclusions for study under incident and transmitted light is challenging and time-consuming, with most samples brittle and opaque. Thus, we stabilize and clear the amber lumps using epoxy preparation under vacuum before grinding and imaging under light microscopy. To date we have recovered 63 arthropods, as weIl as plant remains, fungi, and nematodes. Arachnids include diverse mites (Mesostigmata, Oribatida, Astigmata, and Prostigmata), a variety of spiders and web remains with prey, and a pseudoscorpion. Sorne Collembola were identified as belonging to the family Entomobryidae (Entomobryomorpha). Insects include members of the families Dermestidae (Coleoptera), Mymaridae and Scelionidae (Hymenoptera), Veliidae (Heteroptera), Ceratopogonidae (Forcipomyia) and Mycetophilidae (Diptera), as well as Psocoptera, and Lepidoptera. The most abundant fungi in New Zealand amber are hyphomycetes similar to the genus Casparyotorula from European Palaeogene ambers and we discovered similar fungi growing on resin of the extant Agathis australis, the iconic New Zealand Kauri. Furthermore, specimens of the genus Metacapnodium (Capnodiales) represent the first Southem Hemisphere fossil sooty moulds; saprophytic ascomycetes with brown hyphae, often forming extensive subicula on living plant surfaces. These fungi are ubiquitous and diverse in New Zealand today. Many of these new amber fossils represent groups with an otherwise poor fossil record for the entire Southem Hemisphere. The systematic and ecological diversity of the inclusions highlights the potential of New Zealand amber for reconstructing past terres trial ecosystems of Zealandia, one of the biogeographically crucial former Gondwanan landmasses.

International audience; Speleothem-like deposits that develop underground in urban areas are an archive of the environmental impact of anthropic activities that has been little studied so far. In this paper, the sulfate content in shallow groundwater from northern Paris (France) is compared with the sulfur content in two 300-year-old urban carbonate deposits that grew in a historical underground aqueduct. The present-day waters of the aqueduct have very high sulfur and calcium contents, suggesting pollution from gypsum dissolution. However, geological gypsum levels are located below the water table. Sulfur content was measured by micro-X-ray fluorescence in these very S-rich carbonate deposits (0.5 to 1% of S). A twofold S increase during the second half of the 1800s was found in both samples. These dates correspond to two major periods of urbanization above the site. We discus three possible S sources: anthropic sources (industries, fertilizers…), volcanic eruptions and input within the water through gypsum brought for urbanization above the studied site (backfill with quarry waste) since the middle of the 19th century. For the younger second half of the studied section, S input from gypsum brought during urbanization was confirmed by the study of isotopic sulfur composition (δ34S = + 15.2‰ at the top). For the oldest part, several sulfur peaks could be related to early industrial activity in Paris, that caused high local air pollution, as reported in historical archives but also to historical gypsum extraction. This study provides information on the origin and timing of the very high SO42 − levels measured nowadays within the shallow groundwater, thus demonstrating the interest in using carbonate deposits in urban areas as a proxy for the history of urbanization or human activities and their impact on water bodies.

International audience; Extra sets of 2D multi-channel seismic and chronostratigraphic data allowed us to undertake analyses of source to sink processes and triggering mechanisms of the gigantic megaslides previously documented off the NW and SE steep slope settings of the Foz do Amazonas basin. As these megaslides comprise two sets of stacked allochthonous masses within the Upper Miocene-Quaternary sedimentary record, they are now described as Mass-Transport Complexes (MTCs) and have been renamed the Amapá Megaslide Complex (AMC) and the Pará-Maranhão Megaslide Complex (PMMC). Individual megaslides of both MTCs can mobilize up to kilometre-thick sedimentary series as allochthonous masses with distinct flow directions, degrees of sediment disruption and internal coherence. Megaslides spread downslope over areas as large as thousands of km2, attaining dimensions comparable to the world's largest mass-transport deposits. Among all the megaslides, the basal and largest AM1 megaslide (AMC) stands as a quite unique example of mass-transport deposit in the basin, interpreted as a dominant carbonate allochthonous mass sourced from a mixed carbonate-siliciclastic platform. The instability was probably triggered between the late Miocene and the end of the Early Pliocene by the gravitational collapse of the mixed platform under its own weight, after successive subaerial exposures which generated karstification processes. Siliciclastic-type megaslides, on the other hand, are all sourced from large upslope slide and/or rotated blocks (up to 60 km wide in the case of the PMMC). The detachment of upslope blocks was triggered by structurally-induced seabed movements during the Mid Pliocene-Pleistocene (in the case of the PMMC) and during the Pleistocene (in the case of the AMC). All mapped features support the interpretation of sedimentary blocks which have undergone long lasting deformation, having been variably folded and faulted by the sliding along an overpressured condensed section (H3 horizon). H3 horizon equally acts as the upper décollement level for the gravity tectonic system that operates on the regional scale of the Foz do Amazonas basin. In such a context, the results of this study evidence complex links between variable modes and scales of gravity processes (gravity tectonics and MTCs emplacements), all induced by instability created from a condensed section prone to produce pore fluid overpressure. And yet, seismic attributes of the décollement H3 across the slope, characterized by a reflector of negative polarity of high amplitude, indicate that the potential for similar large scale sediment failures continues to exist across the AMC and PMMC.

Olivine is the principal mineral of kimberlite magmas, and is the main contributor to the ultramafic composition of kimberlite rocks. Olivine is partly or completely altered in common kimberlites, and thus unavailable for studies of the origin and evolution of kimberlite magmas. The masking effects of alteration, common in kimberlites worldwide, are overcome in this study of the exceptionally fresh diamondiferous kimberlites of the Udachnaya-East pipe from the DaldynAlakit province, Yakutia, northern Siberia. These serpentine-free kimberlites contain large amounts of olivine (similar to 50 vol.%) in a chloridecarbonate groundmass. Olivine is represented by two populations (olivine-I and groundmass olivine-II) differing in morphology, colour and grain size, and trapped mineral and melt inclusions. The large fragmental olivine-I is compositionally variable in terms of major (Fo(8594)) and trace element concentrations, including H2O content (10-136 ppm). Multiple sources of olivine-I, such as convecting and lithospheric mantle, are suggested. The groundmass olivine-II is recognized by smaller grain sizes and perfect crystallographic shapes that indicate crystallization during magma ascent and emplacement. However, a simple crystallization history for olivine-II is complicated by complex zoning in terms of Fo values and trace element contents. The cores of olivine-II are compositionally similar to olivine-I, which suggests a genetic link between these two types of olivine. Olivine-I and olivine-II have oxygen isotope values ( +5.6+/- 0.1 parts per thousand VSMOW, 1 SD) that are indistinguishable from one another, but higher than values (+5.18 +/- 0.28 parts per thousand) in typical mantle olivine. These elevated values probably reflect equilibrium with the Udachnaya carbonate melt at low temperatures and O-18-enriched mantle source. The volumetrically significant rims of olivine-II have constant Fo values (89.0 +/- 0.2 mol%), but variable trace element compositions. The uniform Fo compositions of the rims imply an absence of fractionation of the melts Fe2+/Mg, which is possible in the carbonatite meltolivine system. The kimberlite melt is argued to have originated in the mantle as a chloridecarbonate liquid, devoid of ultramafic or basaltic aluminosilicate components, but became olivine-laden and olivine-saturated by scavenging olivine crystals from the pathway rocks and dissolving them en route to the surface. During emplacement the kimberlite magma changed progressively towards an original alkali-rich chloridecarbonate melt by extensively crystallizing groundmass olivine and gravitational separation of solids in the pipe.

International audience; The Messinian Salinity Crisis resulted from desiccation of the Mediterranean Sea after its isolation from the Atlantic Ocean at the end of the Miocene. Stratal geometry tied to borehole data in the Gulf of Lions show that the pre-crisis continental shelf has been eroded during a major sea-level fall and that sedi-ments from this erosion have been deposited in the basin. This detrital package is onlapped by high amplitude seismic reflectors overlain by the "Messinian Salt" and the "Upper Evaporites". Towards the shelf, the transition between regressive deposits and overlying onlapping sediments is characterised by a wave-ravinement surface, suggesting that a significant part of the onlapping reflectors and overlying Messinian Evaporites were deposited during a relatively slow landward migration of the shoreline. The clear boundary between the smooth wave-ravinement surface and the subaerial Messinian Erosional Surface observed on the Gulf of Lions shelf and onshore in the Rh^ one valley is interpreted to have resulted from a rapid acceleration of the Mediterranean sea level rise at the end of the Messinian Salinity Crisis. Numerical simulation of this cycle of sea level change during the Messinian Salinity Crisis and of precipitation of thick evaporites during the slow sea level rise shows that this scenario can be modelled assuming a value of evaporation minus precipitation of 1.75 m 3 /m 2 /yr in the deep Mediterranean basins.

We present the first comprehensive seismic‐stratigraphic analysis of Fairway Basin, which is situated on the rifted continent of Zealandia in the Tasman Sea, southwest Pacific, between Australia and New Caledonia. The basin is 700 km long, 150 km wide, and has water depths of 500–3000 m. We describe depositional architecture and paleogeographic evolution of this basin. Basin formation was concurrent with two tectonic events: (i) Cretaceous rifting during eastern Gondwana breakup and (ii) initiation and Cenozoic evolution of Tonga–Kermadec subduction system to the east of the basin. To interpret the basin history we compiled and interpreted 2D seismic‐reflection profiles and make correlations with DSDP boreholes and the geology of New Caledonia. Five seismic‐stratigraphic units were defined. The deepest and oldest unit, FW3, folded and faulted can be correlated with volcaniclastic sediments and magmatic rocks in New Caledonia that are associated with Mesozoic Gondwana margin subduction. Alternatively, given the basin location 200–300 km west of New Caledonia and inboard of the ancient plate boundary, the unit could have formed as Gondwana intra‐continental basin with no known correlative. The overlying unit FW2b records syn‐rift deposition, probably associated with Cretaceous Gondwana breakup. Subaerial erosion supplied terrigenous sediment into the deltas in the northern part of the basin, as suggested by the truncation surfaces on the basement highs and sigmoid reflector geometries within unit FW2b respectively. Above, unit FW2a records post‐rift sedimentation and passive subsidence as the Tasman Sea opened and the Fairway Basin drifted away from Australia. Subsidence led to the flooding of the basement highs and burial of wave‐cut surfaces. Eocene compressive deformation resulted in minor folding and tilting within the Fairway Basin and was associated with the formation of many diapiric structures. The top of unit FW2 is an extensive unconformity that is associated with erosion and truncation on surrounding ridges. Above this unconformity, unit FW1b is interpreted as a turbidite system sourced from topography created during the Eocene tectonic event, which we interpret as being related to Tonga–Kermadec subduction initiation. Pelagic carbonate sedimentation is now prevalent. Unit FW1a has progressively draped the basin during Oligocene to Pleistocene subsidence. Many small volcanic cones were erupted during this final phase of subsidence, either as a delayed consequence of subduction initiation, or related to Tasmantid and Lord Howe hotspot trails. The northern Fairway Ridge remains close to sea level and its reef system continues to supply carbonate detrital sediments into the basin, most likely during sea‐level lowstands. Fairway Basin contains a nearly continuous record of tectonic and paleoclimatic events in the southwest Pacific since Cretaceous time. Its paleogeographic history is a key piece in the puzzle for understanding patterns of regional biodiversity in the southwest Pacific.

International audience; This paper presents 34 geochemical analyses, 24 Ar‐Ar ages, and two U‐Pb ages of igneous rocks from the back‐arc basins and submarine ridges in the Coral Sea‐New Caledonia region. The D'Entrecasteaux Ridge is a composite structural feature. Primitive arc tholeiites of Eocene age (34–56 Ma) are present along a 200 km length of the ridge and arguably were part of the initial line of subduction inception between Fiji and the Marianas; substantial Eocene arc edifices are only evident at the eastern end where Bougainville Guyot andesite breccias are dated at 40 ± 2 Ma. The South Rennell Trough is confidently identified as a 28–29 Ma (early Oligocene) fossil spreading ridge, and hence, the flanking Santa Cruz and D'Entrecasteaux basins belong in the group of SW Pacific Eocene‐Early Miocene back‐arc basins that include the Solomon Sea, North Loyalty, and South Fiji basins. The rate and duration of spreading in the North Loyalty Basin is revised to 43 mm/yr between 28 and 44 Ma, longer and faster than previously recognized. The direction of its opening was to the southeast, that is, parallel to the continent‐ocean boundary and perpendicular to the direction of coeval New Caledonia ophiolite emplacement. Medium‐ and high‐K alkaline lavas of 23–25 Ma (late Oligocene) age on the northern Norfolk Ridge are an additional magmatic response to Pacific trench rollback.

International audience; Passive margins are characterised by an important tectonic and thermal subsidence, which favours a good preservation of sedimentary sequences. This sedimentation in turn enhances the subsidence because of loading effects. We present here a direct method based on sedimentary markers seen on seismic data, to evaluate total subsidence rates from the coast to the outer shelf and to the deep basin in the Gulf of Lion, from the beginning of massive salt deposition up to present day (the last circa 6 Ma) with minimal theoretical assumptions. On the shelf, the Pliocene-Quaternary subsidence shows a seaward tilt reaching a rate of 240 m/Ma (±15 m/Ma) at the shelf break (70 km from the present day coastline) (i.e. a total angle of rotation of 0.88° (0.16°/Ma)). We were also able to measure and quantify for the first time the isostatic rebound of the outer shelf due to the Messinian salinity crisis (MSC). This value is very high and reaches up to 1.3 km of uplift during the crisis around the Herault-Sète canyon heads (around 1.8 km/Ma). On the slope, we also find a seaward tilting subsidence from Km 90 to Km 180 with a measured angle of 1.41°. From 180 km to the deepest part of the basin, the total subsidence is then almost vertical and reaches 960 m/Ma (±40 m/Ma) during the last 5.7 Ma (±0.25 Ma) in the deepest part of the basin. The subsidence is organised in three compartments that seem related to the very deep structure of the margin during the opening of the Liguro-provencal basin. These very high total subsidence rates enable high sedimentation rates along the margin with sediments provided by the Rhône river flowing from the Alps, which in turn enable the detailed record of climate evolution during Pliocene-Quaternary that make of the Gulf of Lion a unique archive.

Correlation between particulate organic carbon (POC) and calcium carbonate sinking through the deep ocean has led to the idea that ballast provided by calcium carbonate is important for the export of POC from the surface ocean. While this idea is certainly to some extent true, it is worth considering in more nuance, for example, examining the different effects on the aggregation and sinking of POC of small, non-sinking calcite particles like coccoliths and large, rapidly sinking calcite like planktonic foraminiferan tests. We have done that here in a simple experiment carried out in roller tanks that allow particles to sink continuously without being impeded by container walls. Coccoliths were efficiently incorporated into aggregates that formed during the experiment, increasing their sinking speed compared to similarly sized aggregates lacking added calcite ballast. The foraminiferan tests, which sank as fast as 700 m d−1, became associated with only very minor amounts of POC. In addition, when they collided with other, larger, foraminferan-less aggregates, they fragmented them into two smaller, more slowly sinking aggregates. While these effects were certainly exaggerated within the confines of the roller tanks, they clearly demonstrate that calcium carbonate ballast is not just calcium carbonate ballast- different forms of calcium carbonate ballast have notably different effects on POC aggregation, sinking, and export.

During the early years of the Iceland Deep Drilling Project (IDDP), development of three distinctive technological and scientific approaches were formalised and then carried out until 2010 within a European funded project called HiTI (high temperature instruments for supercritical geothermal reservoir characterisation and exploitation). These approaches were: (1) development of several downhole instruments allowing them to function up to 300 °C and 400 °C, (2) identification of two new Na/Li cation ratio geothermometric relationships valid at very high temperature, (3) tracer testing with high temperature tolerant organic isomers and finally and (4) basalt rock deformation and petrophysical properties laboratory investigations at high temperature and pressure conditions. © 2013 Elsevier Ltd. All rights reserved.

Fragilariopsis kerguelensis (O'Meara) Hustedt is the most abundant open ocean diatom species in Southern Ocean sediments and its average valve area has recently been used to infer glacial–interglacial paleoceanographic conditions. Studies from the Atlantic sector of the Southern Ocean demonstrated how larger average valve area of F. kerguelensis during the Last Glacial compared to the interglacial possibly relate to greater availability of iron (through wider sea ice coverage and higher eolian dust input). We present here data on average valve area of F. kerguelensis from three sediment cores covering the last ∼42 cal ka BP from different zones of the Southern Ocean. Our records confirm previous results from the Atlantic sector, but highlight a different pattern from the Indian sector where the largest valves of F. kerguelensis are encountered during the Holocene. Fragilariopsis kerguelensis average valve area variations in the Antarctic Polar Front (APF) of the Atlantic sector and Subantarctic Front of the Indian sector are in phase with records of opal burial while this correlation does not hold for the APF of the Indian sector. Variations in circum-polar upwelling were suggested as the main controlling factor of opal production during the last 20,000 years. We here hypothesize that high nutrient input from the Antarctic Peninsula during the last deglaciation may have exerted a stronger control on F. kerguelensis average valve area and opal export in the Atlantic sector of the Southern Ocean than inferred changes in circum-polar upwelling.

International audience; Detailed analysis of the stratigraphic architecture and deformation of lower trench-slope sedimentary basins permits the tectonic evolution of subduction margins to be constrained. This study utilises offshore seismic reflection profiles and onshore outcrop data to examine the entire lower trench-slope of the Hikurangi subduction margin in the eastern North Island, New Zealand. Our results constrain the main spatial and temporal changes of facies and sedimentary units since about 25 Ma. We demonstrate that the geometries and locations of Miocene to Quaternary sedimentary basins are controlled by tectonic activity and reflect stages of subduction wedge development. Four types of sedimentary basins have been recognized: 1) flysch basins with local olistostromes at the front of seaward propagating thrust sheets; 2) 5-10 km wide turbidite-rich trench-slope basins between uplifting structural ridges (i.e. anticlines) associated with shortening within 100 km of the subduction front at the seafloor; 3) 30-40 km wide trench-slope basins associated with an upslope increase in thrust and ridge spacing; and 4) mixed siliciclastic-carbonate shelves formed in association with margin uplift after filling of the wider (30-40 km) trench-slope basins. The lateral and vertical successions of basin geometries and sedimentary infill are consistent with the overall progressive uplift of the subduction wedge. Formation of some of the wide trench-slope basins may be accompanied by significant local subsidence and normal faulting synchronous with active shortening at the subduction front. Margin-wide normal faulting during the Middle-Late Miocene may have formed due to upslope collapse related to tectonic erosion. All of the basins studied contain major unconformities at their base and top, with basin strata deposited over about 2-8 Myr. The short life span of these lower trench-slope sedimentary basins is consistent with a succession of short paroxysmal tectonic episodes rather than continuous deformation for the duration of subduction. Stratigraphic discontinuities within basins (e.g., facies changes and reversal of paleo-currents) also record short-term tectonic events (c. 1-2 Myr) on the basin-bounding structures and attest to the episodic nature of upper-plate deformation in response to continuous subduction beneath the active margin.

International audience; We present here a synthesis of the evolution of rifted continental margin systems in the Gulf of Aden. These margins are volcanic to the west of the Gulf of Aden, where they are influenced by the Afar hotspot, and non-volcanic east of longitude 46° E. The combined use of magnetics, gravity, seismic reflection, field observations (tectonic, stratigraphic and sedimentological) and oil well data allowed us to obtain better constraints on the timing of continental rifting and seafloor spreading. From the Permo-Triassic to the Oligocene, the Arabian-African plate was subject to distributed extension, probably due, at least from the Cretaceous, to tensile stresses related to the subduction of the Tethysian slab in the north. In Late Eocene-Early Oligocene, 34-33 Ma ago, rifting started to localise along the future area of continental breakup. Initially guided by the inherited basins, continental rifting then occurred synchronously over the entire gulf before becoming localised on the northern and southern borders of the inherited grabens, in the direction of the Afar hotspot. In the areas with non-volcanic margins (in the east), the faults marking the end of rifting trend parallel to the inherited grabens. Only the transfer faults cross-cut the inherited grabens, and some of these faults later developed into transform faults. The most important of these transform faults follow a Precambrian trend. Volcanic margins were formed in the west of the Gulf, up to the Guban graben in the southeast and as far as the southern boundary of the Bahlaf graben in the northeast. Seaward dipping reflectors can be observed on many oil industry seismic profiles. The influence of the hotspot during rifting was concentrated on the western part of the gulf. Therefore, it seems that the western domain was uplifted and eroded at the onset of rifting, while the eastern domain was characterised by more continuous sedimentation. The phase of distributed deformation was followed by a phase of strain localisation during the final rifting stage, just before formation of the Ocean-Continent Transition (OCT), in the most distal graben (DIM graben). About 20 Ma ago, at the time of the continental break-up, the emplacement of the OCT started in the east with exhumation of the subcontinental mantle. Farther west, the system was heated up by the strong influence of the Afar hotspot, which led to breakup with much less extension. In the Gulf of Aden (s.str), up to the Shukra El Sheik fracture zone, oceanic spreading started 17.6 Ma ago. West of this fracture zone, oceanic accretion started 10 Ma ago, and 2 Ma ago in the Gulf of Tadjoura. Post-rift deformation of the eastern margins of the Gulf of Aden can be seen in the distal and proximal domains. Indeed, the substantial post-rift uplift of these margins could be associated with either the continental break-up, or activity of the Afar hotspot and related volcanic/magmatic activity. Uplift of the northern proximal margin was still active (e.g. stepped beach rocks exposed at 60 m of 2 Ma; 30 m of 35,200 years; 10 and 2 m) and active volcanoes can be inferred at depths of between 70 and 200 km beneath the margin (at 5-10 km distance from the coast). On the distal margin, heat flow measurements show a high value that is associated with post-rift volcanic activity and the development of a volcano (with flows and sills) shortly after the formation of the OCT. The Afar hotspot is therefore important for several reasons. It allows the localisation of deformation along the Red Sea/Aden system and the rapid opening of the Gulf after the continental break-up; its influence also seems to persist during the post-rift period.

International audience; The study of the deep structure and evolution of passive continental margins is important for the understanding of rifting processes and the formation of associated sedimentary basins. Since the classical models of McKenzie (1978) and Wernicke (1985), understanding how passive continental margins form, that is to say mainly the way that continental lithosphere is thinned leading to subsidence, remains one of the main challenges in the Earth sciences. Many recent observations and discoveries have modified our basic views of margin formation. The conservational models paradigm (i.e., simple shear, pure shear, or polyphase models), which exclude exchanges between lower continental crust and upper mantle and which are usually proposed to explain lithospheric stretching and consequent crustal thinning of passive continental margins, fail to completely explain all these observations. Furthermore, these models imply a large amount of horizontal movement, movements not observed in the field. In consequence, new concepts need to be built and tested.

Bache, François ... et. al.-- 29 pages, 22 figures, 1 table, additional supporting information may be found in the online version of this article: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2117.2011.00521.x/suppinfo, The Messinian Salinity Crisis is well known to have resulted from a significant drop of the Mediterranean sea level. Considering both onshore and offshore observations, the subsequent reflooding is generally thought to have been very sudden. We present here offshore seismic evidence from the Gulf of Lions and re-visited onshore data from Italy and Turkey that lead to a new concept of a two-step reflooding of the Mediterranean Basin after the Messinian Salinity Crisis. The refilling was first moderate and relatively slow accompanied by transgressive ravinement, and later on very rapid, preserving the subaerial Messinian Erosional Surface. The amplitude of these two successive rises of sea level has been estimated at ≤500 m for the first rise and 600-900 m for the second rise. Evaporites from the central Mediterranean basins appear to have been deposited principally at the beginning of the first step of reflooding. After the second step, which preceeded the Zanclean Global Stratotype Section and Point, successive connections with the Paratethyan Dacic Basin, then the Adriatic foredeep, and finally the Euxinian Basin occurred, as a consequence of the continued global rise in sea level. A complex morphology with sills and sub-basins led to diachronous events such as the so-called 'Lago Mare'.This study helps to distinguish events that were synchronous over the entire Mediterranean realm, such as the two-step reflooding, from those that were more local and diachronous. In addition, the shoreline that marks the transition between these two steps of reflooding in the Provence Basin provides a remarkable palaeogeographical marker for subsidence studies. © 2011 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists, This work is a contribution to ANR ‘EGEO’ Project, to CNRS/INSU ‘Actions Marges’ Project (AMEDITER), and to ‘Bassins ne´oge`nes et manteau en Méditerranée’ (TerMEx CNRS/INSU)

International audience; Passive seismic imaging of the earth is a rapidly developing field of study. Recent advances in noise cross correlation techniques allow imaging of isotropic surface-wave and shear-wave velocities in areas where earthquake numbers and distributions are insufficient to implement traditional earthquake based tomography. Furthermore, advances in the theory underpinning surface wave inversion have led to depth-dependent mapping of seismic anisotropy in the lithosphere and upper asthenosphere. We show that by merging these two rapidly advancing fields we can invert noise-based phase velocity measurements for azimuthally anisotropic phase speed, thereby providing a highly resolved image of layered azimuthal anisotropy in continental crust. We apply this new algorithm in the western Alps, an area of complex lithospheric structure. Alpine crustal thickening results from continental collision, indentation of the Ivrea mantle into the middle crust of the European plate, rollback of the European lithospheric mantle, and crustal slicing. We find that anisotropy beneath the central Alps is stratified in two layers -- one with an orogen-parallel fast direction above ∼ 30 km depth and another with a strong orogen-perpendicular fast direction at greater depth. Although our resolution is reduced outside the central Alps, we map orogen-parallel anisotropy in the crust of the northern Alpine foreland. We interpret the results in the central Alps as first-order evidence for a model of azimuthal anisotropy in which (1) near-vertical emplacement of crustal slices following detachment of the lithospheric mantle from the crust gives rise to orogen-parallel fast directions of wave propagation in the crust, and (2) dominantly horizontal tectonics in the thickened crustal root and uppermost mantle yield orogen-perpendicular fast directions at greater depth.

International audience; New U-Pb dating of detrital zircon and geochemical features of Permian-Mesozoic arc-derived volcanic rocks and volcaniclastic turbidites (greywackes), when compared to the volcanic rocks associated with unconformable Late Cretaceous shallow-water sediments, reveal that subduction in New Caledonia, once thought to be extinct in the Late Jurassic (ca. 150 Ma), was still active at least from ca. 130 Ma to 95 Ma. The accumulation of volcanic arc-derived sediments during the late Early Cretaceous suggests that, as in New Zealand, active margin activity went on for a short time in spite of the assumed subduction jamming by the Hikurangi plateau at ca.100 Ma. Meanwhile, the rift-related magmatic activity that preceded the marginal breakup migrated eastward: from ca. 130 Ma (130-95 Ma) in eastern Australia, 110 Ma (110-82 Ma) in New Zealand, and finally ca. 89 Ma (89-83 Ma) in New Caledonia, and generated large volumes of silicic magma. In contrast, marginal basins opened synchronously at ca. 83 Ma when the stretched continental crust finally broke out. In general, intraplate and volcanic-arc signatures coexisted in Cretaceous syn-rift magmas. Therefore, the Australian marginal breakup appears to be the final effect of continuous southward unzipping of Gondwana that interfered with the subduction-modified mantle wedge of the Mesozoic active margin. The occurrence of lateral flow of the upper asthenospheric mantle due to the rapidly eastward migrating Australian plate margin possibly prevented the formation of a volcanic arc at the eastern end of the system.

We present new analytical data from lavas and associated rocks dredged and/or drilled from the South Fiji Basin, Northland Plateau, Colville Ridge and Havre Trough. These results provide much-needed ground truth about the geology, age and tectonic evolution of the Cenozoic submarine ridges and basins between the active intraoceanic Tonga–Kermadec arc, and rifted continental borderlands of New Zealand, the Norfolk Ridge and New Caledonia. Key results from this study include: (1) Ar–Ar dates on Minerva Abyssal Plain oceanic crust suggest that the ages of magnetic anomalies in the South Fiji Basin have been overestimated by earlier workers; (2) subduction-related lavas are widespread across the region, are not presently organised into arc-like chains, and cluster in the age range 22–18 Ma (Early Miocene); (3) the oldest subduction-related lavas occur in the western part of the region (32–26 Ma: Norfolk and Three Kings Ridge); (4) shoshonites, interpreted as rifted arc lavas, were erupted in a narrow 20–21 Ma interval over a wide area. Put together, these results indicate high magmatic flux and large and rapid horizontal tectonic translations and basin opening from 18–23 Ma in the region immediately north of New Zealand. We explain the Miocene tectonomagmatic development of the region by a model of rapid rollback of a single, east-facing Pacific arc–trench system that became established after Northland Allochthon emplacement. Critical testing of this, versus other, tectonic models must await drilling and dating of thus-far unsampled Kupe Abyssal Plain crust.

International audience; Lodine geyser, located in the Waimangu Geothermal Valley (New Zealand), has been studied by both passive electrical and seismic methods. The activity of the geyser was monitored at various distances from the vent using self-potential method. The self-potential signals display cyclic negative variations with respect to a baseline drawn when the geyser is quiet. The minimum in the self-potential signals coincides with the maximum overflow. We provide a numerical model able to explain both the polarity and magnitude of the observed signal. This model is based on the fluctuations of the hydraulic head in the conduit of the geyser; the divergence of the streaming current density is created at the interface between the pipe and the surrounding rock. Passive seismic experiments were used to localize ambient noise sources. These signals have been processed with the so-called Matched-Field Processing technique (MFP); a dominant source emerged from this processing, that we characterized in range and depth with a good accuracy.

The Alpine Fault zone in New Zealand marks a major transpressional plate boundary that is late in its typical earthquake cycle. Understanding the subsurface structures is crucial to understand the tectonic processes taking place. A unique seismic survey including 2D lines, a 3D array, and borehole recordings, has been performed in the Whataroa Valley and provides new insights into the Alpine Fault zone down to ∼2 km depth at the location of the Deep Fault Drilling Project (DFDP)‐2 drill site. Seismic images are obtained by focusing prestack depth migration approaches. Despite the challenging conditions for seismic imaging within a sediment filled glacial valley and steeply dipping valley flanks, several structures related to the valley itself as well as the tectonic fault system are imaged. A set of several reflectors dipping 40°–56° to the southeast are identified in a ∼600 m wide zone that is interpreted to be the minimum extent of the damage zone. Different approaches image one distinct reflector dipping at ∼40°, which is interpreted to be the main Alpine Fault reflector located only ∼100 m beneath the maximum drilled depth of the DFDP‐2B borehole. At shallower depths (z, Plain Language Summary: The Alpine Fault in New Zealand is a major plate boundary, where a large earthquake will likely occur in the near future. Thus, it is important to understanding the detailed processes of how and where such an earthquake occurs. Many scientists are involved in this work, particularly in the attempt of drilling through the fault zone with a ∼900 m deep borehole. We analyzed new seismic data from this area using sensors in the borehole and at the surface to record small ground movements caused by a vibrating surface source causing waves that travel through the ground. From these data, we obtained a detailed image of the structures in the subsurface, for the first time in 3D, by applying advanced analysis methods. Hence, we can better understand the shape of the glacial valley and of the fault zone, that is, the local structures of the continental plate boundary. We interpret at least 600 m wide zone of disturbed rocks and identify a potential major fractured plane down to about 1 km depth. Our studies may help to understand structures that host earthquakes in this area., Key Points: We use focusing prestack depth migration with detailed seismic data to analyze the complex subsurface environment of the Alpine Fault zone. Seismic images show Alpine Fault zone related reflectors at a depth of ∼0.2–1 km dipping ∼40°–56° around the DFDP‐2B borehole. Complex structures within the glacial Whataroa Valley are imaged showing steep valley flanks, faults, and internal sedimentary horizons., German Research Foundation (DFG), Earthquake Commission (EQC) http://dx.doi.org/10.13039/100012181, NSERC discovery and Canada Research Chairs Program, Canadian Foundation for Innovation

Focused gas migration through the gas hydrate stability zone in vertical gas conduits is a global phenomenon. The process can lead to concentrated gas hydrate formation and seafloor gas seepage, which influences seafloor biodiversity and ocean biogeochemistry. However, much is unknown about how gas and gas hydrate co‐exist within and around gas conduits. We present seismic imaging of the gas hydrate system beneath a four‐way closure anticlinal ridge at New Zealand's southern Hikurangi subduction margin. Gas has accumulated beneath the base of gas hydrate stability to a thickness of up to ∼240 m, which has ultimately led to hydraulic fracturing and propagation of a vertical gas conduit to the seafloor. Despite the existence of an array of normal faults beneath the ridge, these structures are not exploited as long‐range gas flow conduits. Directly beneath the conduit, and extending upward from the regional base of gas hydrate stability, is a broad zone characterized by both negative‐ and positive‐polarity reflections. We interpret this zone as a volume of sediment hosting both gas hydrate and free gas, that developed due to partial gas trapping beneath a mass transport deposit. Similar highly reflective zones have been identified at the bases of other gas conduits, but they are not intrinsic to all gas conduits through gas hydrate systems. We suggest that pronounced intervening sealing units within the gas hydrate stability zone determine whether or not they form., Plain Language Summary: Gas hydrates are ice‐like substances composed of natural gas and water. They form between sediment grains underneath large regions of the Earth's seafloor. An important reason to study gas hydrates is that they partly control the way that methane gas flows through sediments and out of the seafloor. It is this flow of methane that sustains some diverse biological communities on the seafloor and affects the chemistry of the oceans. In this study, we use reflected sound waves to explore how gas flow beneath the seafloor depends on the way in which sedimentary layers are folded and fractured. Our data reveal a 240‐m thick reservoir of gas that is trapped in a large sedimentary fold, ∼500 m beneath the seafloor. The buoyancy of the gas has caused a vertical fracture zone to propagate upward to the seafloor, where gas bubbles are venting into the ocean. Further, our data suggest that a broad accumulation of gas hydrates (together with gas) has formed beneath the vertical fracture zone. This gas hydrate deposit may grow larger with time, and it will continue to influence the way that gas flows through the sediments., Key Points: 240 m thick free gas column accumulated beneath the base of hydrate stability, which led to hydraulic fracturing and gas chimney formation. Broad zone of free gas and gas hydrate formed beneath the gas chimney, extending upward from the regional base of hydrate stability. Such zones of hydrate and free gas likely form due to pronounced lithological contrasts (sealing layers) within the hydrate stability zone., New Zealand's Ministry for Business Innovation and Employment (MBIE) http://dx.doi.org/10.13039/501100004629

International audience; The Comoros archipelago is an active geodynamic region of intra-plate volcanism within which the youngest and oldest islands (Grande Comore and Mayotte respectively) are characterized by recent volcanic activity. The frequent eruptions of the large shield volcano Karthala on Grande Comore (last eruption 2007), and the recent birth of a large submarine volcano since 2018 at the submarine base of Mayotte are associated with permanent fumarolic emissions, bubbling gas seeps, and soil gas emissions, which are studied in detail here for the first time. CO2 fluxes and chemical and isotopic gas compositions acquired during two surveys in 2017 and 2020 are integrated with older datasets collected between 2005 and 2016, permitting the identification of a possible influence of the recent volcanic and magmatic activity at Mayotte.At Karthala, high gas fluxes with high temperature, and a marked magmatic signature are concentrated close to the summit crater area, while only weaker emissions with a stronger biogenic signature are found on the volcano flanks. At Mayotte, lower temperature and higher CH4 content are recorded in two main seep areas of CO2-rich fluid bubbling, while soil emissions on land record a higher proportion of magmatic fluids compared to Karthala. Our preliminary results reveal two quite separate gas emission patterns for each island that are distinct in composition and isotopic signatures, and well-correlated with the present state of volcanic activity. This work may potentially provide support for local observation infrastructures and contribute to the improvement in volcanic and environmental monitoring.

Co-auteur étranger; International audience; Signals of volcanic unrest do not usually provide insights into the timing, size and style of future eruptions, but detailed analysis of past eruptions may uncover patterns that can be used to understand future eruptive behavior. Here, we examine basaltic-andesitic to andesitic eruption deposits from La Soufrière de Guadeloupe, covering a range of eruption styles, ages and magnitudes. Our work is timely given unrest at La Soufrière de Guadeloupe has increased over the last 25 years. We constrain the timescales of magmatic processes preceding four eruptions: 1657 Cal. CE (Vulcanian), 1010 Cal. CE (Plinian), ∼341 Cal. CE (Strombolian) and 5680 Cal. BCE (La Soufrière de Guadeloupe’s first known Plinian eruption). Using crystal-specific analyses of diffusion in orthopyroxenes, we calculate the timescale occurring between the last recharge/mixing event in the magma reservoir and the eruption. We use backscattered electron images, coupled with EMPA of the outermost crystal rim, to derive magmatic timescales. We model the timescale populations as random processes whose probability distributions provide expected (“mean”) timescales and the associated standard errors for each eruption. This provides a new statistical method for comparing magmatic timescales between disparate eruptions. From this, we obtain timescales of magma storage at La Soufriére de Guadeloupe ranging from 18.8 ± 0.37 days to 361 ± 0.40 days, with no clear distinction between eruption style/size and timescales observed. Based on these data, magmatic interaction timescales are a poor predictor of eruption style/size. This study shows that magmatic processes prior to eruption can occur on relatively short timescales at La Soufrière de Guadeloupe. Further to this basaltic-andesitic to andesitic volcanoes can rapidly produce large-scale eruptions on short timescales. These relatively short timescales calculated for volcanic processes at this system constitute a critical new data set and warrant an urgency in enhancing modeling and interpretation capabilities for near-real time monitoring data. These integrated efforts will improve early warning, eruption forecasting and crisis response management for different scenarios, as well as planning for long-term risk reduction.

International audience; Breccia-filled eruption conduits are dynamic systems where pressures frequently exceed critical thresholds, generating earthquakes and transmitting fluids. To assess the dynamics of breccia-filled conduits, we examine lava, ash tuff, and hydrothermal breccia ballistics with varying alteration, veining, fractures, and brecciation ejected during the 27 April 2016 phreatic eruption of Whakaari/White Island. We measure connected porosity, strength, and permeability with and without tensile fractures at a range of confining pressures. Many samples are progressively altered with anhydrite, alunite, and silica polymorphs. The measurements show a large range of connected porosity, permeability, and strength. In contrast, the cracked samples show a consistently high permeability. The cracked altered samples have a permeability more sensitive to confining pressure than the unaltered samples. The permeability of our altered ballistics is lower than surface rocks of equivalent porosity, illustrating that mineral precipitation locally blocked pores and cracks. We surmise that alteration within the conduit breccia allows cracks to form, open and close, in response to pore pressure and confining pressure, providing a mechanism for frequent and variable fluid advection pulses to the surface. This produces temporally and spatially variable geophysical and geochemical observations and has implications for volcano monitoring for any volcano system with significant hydrothermal activity.

Fault displacement hazard assessment is based on empirical relationships that are established using historic earthquake fault ruptures. These relationships evaluate the likelihood of coseismic surface slip considering on‐fault and off‐fault ruptures, for given earthquake magnitude and distance to fault. Moreover, they allow predicting the amount of fault slip at and close to the active fault of concern. Applications of this approach include land use planning, structural design of infrastructure, and critical facilities located on or close to an active fault.To date, the current equations are based on sparsely populated datasets, including a limited number of pre‐2000 events. In 2015, an international effort started to constitute a worldwide and unified fault displacement database (SUrface Ruptures due to Earthquakes [SURE]) to improve further hazard estimations. After two workshops, it was decided to unify the existing datasets (field‐based slip measurements) to incorporate recent and future cases, and to include new parameters relevant to properly describe the rupture.This contribution presents the status of the SURE database and delineates some perspectives to improve the surface‐faulting assessment. Original data have been compiled and adapted to the structure. The database encompasses 45 earthquakes from magnitude 5–7.9, with more than 15,000 coseismic surface deformation observations (including slip measurements) and 56,000 of rupture segments. Twenty earthquake cases are from Japan, 15 from United States, two from Mexico, Italy, and New Zealand, one from Kyrgystan, Ecuador, Turkey, and Argentina. Twenty‐four earthquakes are strike‐slip faulting events, 11 are normal or normal oblique, and 10 are reverse faulting.To pursue the momentum, the initial and common implementation effort needs to be continued and coordinated, and the maintenance and longevity of the database must be guaranteed. This effort must remain based on a large and open community of earthquake geologists to create a free and open access database.

©2018. American Geophysical Union. All Rights Reserved. Sixteen temperature logs were acquired during breaks in drilling of the 893m-deep DFDP-2B borehole, which is in the Alpine Fault hanging-wall. The logs record various states of temperature recovery after thermal disturbances induced by mud circulation. The long-wavelength temperature signal in each log was estimated using a sixth-order polynomial, and residual (reduced) temperature logs were analyzed by fitting discrete template wavelets defined by depth, amplitude, and width parameters. Almost two hundred wavelets are correlated between multiple logs. Anomalies generally have amplitudes

International audience; The Sapanca-Akyazı segment (SAS) is located on western part of the North Anatolian Fault (NAF) of Turkey. It was ruptured together with four other segments during the 17th August 1999 İzmit earthquake (Mw = 7.4) which caused ~145-km-long surface rupture in the east Marmara region. We conducted geomorphological investigations and 2D–3D paleoseismic trenching at 3 different sites near the Sakarya River along the SAS to obtain new data for the timing of past earthquakes and slip rate of this section of the NAF. Detailed investigations using Ground Penetrating Radar on the western bank of the Sakarya River reveal 18.5 ± 0.5 m of right-lateral cumulative offset of an alluvial terrace dated as 850 ± 11 years BP using Optically Stimulated Luminescence. The analysis of trench data from the three different sites of the SAS indicates the occurrence of four surface rupturing past earthquakes including the 1999 İzmit earthquake. According to the radiocarbon dating, these paleo-earthquakes can be correlated with the 1719 CE, 1567 CE, and 1037 CE historical earthquakes and suggest an average recurrence period between 273 and 322 years. The total dextral offset, the age of trench units and the terrace deposits together suggest a 22 ± 3 mm/yr slip rate for this portion of the NAF.

Marine sediment records suggest that episodes of major atmospheric CO2 drawdown during the last glacial period were linked to iron (Fe) fertilization of subantarctic surface waters. The principal source of this Fe is thought to be dust transported from southern mid-latitude deserts. However, uncertainty exists over contributions to CO2 sequestration from complementary Fe sources, such as the Antarctic ice sheet, due to the difficulty of locating and interrogating suitable archives that have the potential to preserve such information. Here we present petrographic, geochemical and microbial DNA evidence preserved in precisely dated subglacial calcites from close to the East Antarctic Ice-Sheet margin, which together suggest that volcanically-induced drainage of Fe-rich waters during the Last Glacial Maximum could have reached the Southern Ocean. Our results support a significant contribution of Antarctic volcanism to subglacial transport and delivery of nutrients with implications on ocean productivity at peak glacial conditions., Contributions of iron sources to Southern Ocean CO2 sequestration during the last glacial period remain uncertain. Here, based on the biogeochemical analysis of subglacial calcites, the authors propose Antarctic volcanism, via subglacial drainage of Fe-rich waters, as a key contributor.

International audience; We study interseismic deformation preceding the Mw8.8 2010 Maule earthquake by means of two-dimensional finite-element modeling. Our goal is to gain insight into the fundamental factors controlling elastic strain build-up and release in subduction zones, and to evaluate different modeling approaches of surface displacement as observed by GPS. We developed a linear elasticity solver that allows us to implement a realistic subducting plate geometry constrained by geophysical data. We test the influence of subducting plate thickness, variations in the updip and downdip limit of a 100% locked interplate zone, elastic parameters, and velocity reduction at the base of the subducted slab. We compared our modeled predictions with interseismic GPS observations along an EW profile crossing the Maule earthquake rupture area, in order to determine best fitting parameters. Our results indicate little inf luence of the subducting plate thickness at a given downdip limit, which itself has a strong influence on surface deformation. However, the fit to observations is achieved only after reducing the velocity at the base of the subducted slab below the trench region to 10% of the far-field convergence rate. We link this novel result to complementary numerical models that gradually evolve toward considering longer timescales and complex rheology in order to evaluate the mechanical meaning of the above mentioned inferred kinematic conditions. This allowed us to link the velocity reduction at the base of subducting slabs with a long-term state of high flexural stress resulting from the mechanical interaction of the slab with the underlying mantle. Even a small amount of theses high deviatoric stresses may transfer towards the upper portion of the slab as strain energy that could participate into the mechanical loading of the megathrust and therefore in triggering large earthquakes there.

International audience; The presence of water at volcanic vents can have dramatic effects on fragmentation and eruption dynamics, but little is known about how the presence of particulate matter in external water will further alter eruptions. Volcanic edifices are inherently "dirty" places, where particulate matter of multiple origins and grainsizes typically abounds. We present the results of experiments designed to simulate non-explosive interactions between molten basalt and various "coolants," ranging from homogeneous suspensions of 0 to 30 mass% bentonite clay in pure water, to heterogeneous and/or stratified suspensions including bentonite, sand, synthetic glass beads and/or naturally-sorted pumice. Four types of data are used to characterise the interactions: (1) visual/video observations; (2) grainsize and morphology of resulting particles; (3) heat-transfer data from a network of eight thermocouples; and (4) acoustic data from three force sensors. In homogeneous coolants with ~20% sediment, heat transfer is by forced convection and conduction, and thermal granulation is less efficient, resulting in fewer blocky particles, larger grainsizes, and weaker acoustic signals. Many particles are droplet-shaped or/and "vesicular," containing bubbles filled with coolant. Both of these particle types indicate significant hydrodynamic magma-coolant mingling, and many of them are rewelded into compound particles. The addition of coarse material to heterogeneous suspensions further slows heat transfer thus reducing thermal granulation, and variable interlocking of large particles prevents efficient hydrodynamic mingling. This results primarily in rewelded melt piles and inefficient distribution of melt and heat throughout the coolant volume. Our results indicate that even modest concentrations of sediment in water will significantly limit heat transfer during non-explosive magma-water interactions. At high concentrations, the dramatic reduction in cooling efficiency and increase in mingling help to explain globular peperite, and provide information relevant to analyses of premixing associated with highly-explosive molten fuel-coolant interactions in debris-filled volcanic vents.

International audience; We present Cu isotope data of hypogene and supergene minerals from the Late Paleocene Spence Cu-Mo porphyry in the Atacama Desert of northern Chile. Chalcopyrite displays a restricted range of δ65Cu values within the values reported for primary porphyry Cu sulfides (+ 0.28‰ to + 0.34‰, n = 6). Supergene chalcocite samples show heavier and remarkably homogeneous δ65Cu values, between + 3.91‰ and + 3.95‰ (n = 6), consistent with previous models of Cu leaching and enrichment in porphyry systems. Secondary Cu minerals from the oxide zone show a wider range of composition, varying from + 1.28‰ and + 1.37‰ for chrysocolla (n = 6) to very light Cu isotope signatures reported for atacamite between -5.72‰ to -6.77‰ (n = 17). These data suggest redox cycling of Cu during supergene enrichment of the Spence Cu deposit, characterized by a first stage of supergene chalcocite formation from acidic, isotopically-heavy leach fluids of meteoric origin down-flowing in a semi-arid climate (44 to ~ 15-9 Ma). Reworking of the initial supergene copper assemblage, during the Pleistocene, by rising neutral and chlorine-rich deep formation waters under well-established hyper-arid climate conditions lead to the formation of atacamite with extremely fractionated Cu compositions. Essentially coeval chrysocolla formed by dissolution of atacamite during short episodes of wetter climatic conditions occurring in the latest Pleistocene.

International audience; Mt. Ruapehu erupted on 25 September 2007 at 20:26 PM NZDT (8:26 UT) generating a steam column to about 15,000 ft (4600 m), a directed ballistic and surge deposit of coarse blocks and ash to the north of the Crater Lake, and initiated lahars in the Whangaehu catchment and Whakapapa ski field. The eruption was recorded on three broadband seismometers and two acoustic pressure sensors which indicated broadly coherent waveform characteristics across the network. The eruption had a duration of less than 1 min as indicated by strong seismic and acoustic pulses. The acoustic wave coincided with observed very long-period (VLP) seismic signal (2–25 s period). The acoustic pulse had a positive pressure (indicating an explosion) and travelled at a velocity of ∼320 m/s. The syn-eruptive VLP was composed of surface waves having strong radial and transverse components. The immediate aftermath of the eruption produced about 4 min of continued high amplitude spasmodic tremor signals that probably resulted from post-explosion phase associated vent backfill/stabilisation. The eruption was preceded by minor volcano-tectonic earthquakes and tremor bursts which began 10 min before the main eruption. Two smaller VLP signals were associated with these tremor pulses at 20:17 and 20:25. These pre-eruptive VLP signals had particle motions indicating body and surface waves from a sub-surface source region. Modelling of the VLP sources using a 3D finite-difference method shows that that the pre-eruption VLP signals are consistent with a volume fluctuation at 3–7 km depth from a radially symmetric source. The main eruption VLP was consistent with a south and downward directed single force in response to a northward directed jet and northward directed ballistic deposits.

International audience; We develop new approaches to calculating 30-year probabilities for occurrence of moderate-to-large earthquakes in Italy. Geodetic techniques and finite-element modelling, aimed to reproduce a large amount of neotectonic data using thin-shell finite element, are used to separately calculate the expected seismicity rates inside seismogenic areas (polygons containing mapped faults and/or suspected or modelled faults). Thirty-year earthquake probabilities obtained from the two approaches show similarities in most of Italy: the largest probabilities are found in the southern Apennines, where they reach values between 10% and 20% for earthquakes of ≥ 6.0, and lower than 10% for events with an ≥ 6.5.

International audience; The Roussillon Basin is a non-silled Miocene sedimentary basin filling a late Oligocene–early Miocene graben. The basin was intensively impacted by the 2 Messinian fluvial erosion, as evidenced in exposed sections, in seismic profiles and in deep boreholes drilled for hydrocarbon exploration. As the basin was open to the Mediterranean Sea, the huge drop in sea level at the peak of the Messinian Salinity Crisis is clearly recorded, along with the subsequent sudden marine reflooding and the resulting prograding sedimentary filling, particularly in Gilbert-type fan deltas. Here, the Messinian Erosional Surface (MES) is accurately mapped in a high-resolution document, which corrects the confusion resulting from the set of 1:50,000 scale regional maps. Aim of the 3D reconstruction of the MES is to modernize geological mapping, a crucial challenge for Mediterranean and peripheral areas. Thanks to a reliable chronostratigraphy provided by planktonic foraminifers, calcareous nannofossils, micro-and macro-mammal remains, paleomagnetism and a 10 Be cosmogenic nuclide-derived study, our reconstruction is one of the most comprehensive models of changes in sea level from 6 to 3 Ma. After the marine reflooding of the Mediterranean Basin at 5.46 Ma, the fluctuations in sea level recorded in the Roussillon Basin were forced by global changes. Following reflooding, the Prades large olistostrome collapsed prepared by the previous exhumation along the Canigou fault. The olistostrome is a good example of a local accident resulting from Messinian events. The exceptional changes in sea level at the peak of the Messinian Salinity Crisis deeply marked the Roussillon Basin, momentarily overprinting the Pyrenean orogenesis. Key words: Roussillon Basin – Messinian subaerial erosion –Zanclean sedimentary filling –Prades olistostrome.

International audience The link between seismicity and degassing is investigated during the VEI 4 eruptions of Merapi volcano (Indonesia) in October and in early November 2010. Seismicity comprised a large number and variety of earthquakes including Volcano-Tectonic events, a sustained period of Long Period Seismicity (LPS), i.e., Long-Period events (LP), Very Long Period events (VLP) and tremor. LPS seismicity is ascribed to the excitation of fluid-filled cavity resonance and inertial displacement of fluids and magma. We investigate here LPS that occurred between 17 October and 4 November 2010 to obtain insights into the volcano eruption processes which preceded the paroxysmal phase of the eruption on 4-5 November. We proceed to the moment tensor inversion of a well-recorded large VLP event during the intrusion phase on 17 October 2010, i.e., before the first explosion on 26 October. By using two simplified models (crack and pipe), we find a shallow source for this VLP event at about 1 km to the south of the summit and less than 1 km below the surface. We analyze more than 90 LP events that occurred during the multi-phase eruption (29 October-4 November). We show that most of them have a dominant frequency in the range 0.2-4 Hz. We could locate 48 of those LP events; at least 3 clusters of LP events occurred successively. We interpret these observations as generated by different fluid-filled containers in the summit area that were excited while magma rose. We also observe significant variations of the complex frequency during the course of the eruption. We discuss these changes in terms of a variable ratio of fluid to solid densities and/or by possible conduit geometry change and/or permeability of the conduit or the edifice and/or by resonance of different fluid-containers during the release of more than 0.4 Tg of SO2 and large but unknown masses of other volcanic gases. Finally, we also discuss how the major explosions of the eruption were possibly triggered by passing waves resulting from regional tectonic earthquakes on 3 and 4 November.

International audience; Since early 2005. Ngauruhoe volcano has produced repeating low-frequency earthquakes with evolving waveforms and spectral features which become progressively enriched in higher frequency energy during the period 2005 to 2009, with the trend reversing after that time. The earthquakes also show a seasonal cycle since January 2006, with peak numbers of events occurring in the spring and summer period and lower numbers of events at other times. We explain these patterns by the excitation of a shallow two-phase water/gas or water/steam cavity having temporal variations in volume fraction of bubbles. Such variations in two-phase systems are known to produce a large range of acoustic velocities (2-300 m/s) and corresponding changes in impedance contrast. We suggest that an increasing bubble volume fraction is caused by progressive heating of melt water in the resonant cavity system which, in turn, promotes the scattering excitation of higher frequencies, explaining both spectral shift and seasonal dependence. We have conducted a constrained waveform inversion and grid search for moment, position and source geometry for the onset of two example earthquakes occurring 17 and 19 January 2008, a time when events showed a frequency enrichment episode occurring over a period of a few days. The inversion and associated error analysis, in conjunction with an earthquake phase analysis show that the two earthquakes represent an excitation of a single source position and geometry. The observed spectral changes from a stationary earthquake source and geometry suggest that an evolution in both near source resonance and scattering is occurring over periods from days to months.

International audience; The Late Cretaceous clastic coastal sediments of New Caledonia are contemporaneous with the latest stages of the eastern Australian marginal rifting. As such, they record the erosion of basement terranes located on uplifted and tilted blocks and a contemporaneous volcanic activity. Detrital zircon populations contain two major components, the younger of which is Early Cretaceous, and the older Early Paleozoic and Precambrian. Following recent advances in the knowledge of detrital zircon content of basement terranes, and at variance with previous interpretations, that hypothesised a possible direct Australian provenance for Precambrian zircons, the detrital zircon record of these syn-rift sediments allows a local recycled provenance to be established. In consequence, this new evidence confirms that New Caledonia was already isolated from Australia as early as Coniacian time (ca. 89-85 Ma) a fact consistent with the development of faunal and floral endemism at that period. The prominent abundance of Early Cretaceous detrital zircons also establishes the importance of a previously unrecorded Early Cretaceous magmatism in the area.

International audience; This paper presents preliminary results for three GPR profiles acquired across the Wellington active strike-slip fault within the Wellington urban area. In this sector, it is suggested that the subsurface geometry (8-10 m) of the fault comprises twomain deforming strands that bound narrow transpressive and transtensive sections. The location of fault planes interpreted from radargrams closely corresponds with the inferred location of the main fault at the ground surface. Despite noise due to the urban settings, GPR proved to be a technique capable of locating fault strands, thus potentially providing useful data in targeting areas for palaeoseismic studies, such as trenching.

International audience; The discovery of new radiolarian localities in the western belt of the Cache Creek terrane in southern British Columbia possibly changes its upper age limit from Late Triassic to Early or Middle Jurassic. It favors a Middle Jurassic, rather than a Late Triassic, age of amalgamation for the Cache Creek terrane and Quesnellia (parts of superterrane I) in southern British Columbia. The new Jurassic ages also mean that the western Cache Creek terrane could be equivalent in age to the Bridge River-Hozameen terrane in British Columbia and to terranes containing the Tethyan fusulinid Yabeina in northwest Washington and the Klamath Mountains of California.

Special issue The Messinian events and hydrocarbon exploration in the Mediterranean.-- Clauzon, Georges ... et. al.-- 30 pages, 19 figures, 2 plates, 3 tables, The Sorbas Basin is the land reference of the Messinian Salinity Crisis (MSC) that affected the Mediterranean Sea in the latest Miocene. Its stratigraphy has been re-visited using calcareous nannofossils and planktonic foraminifers, which provide a reliable biostratigraphic frame and lead to particularly specify the relationships between the Sorbas and Zorreras members with Yesares evaporites. The evaporites overlie a shallowing upward sequence ending with the deposition of the Reef Unit and Terminal Carbonate Complex (TCC) on the periphery of the basin. The reefal carbonates of the TCC are overlain by clastic deposits that are foreset beds of post-MSC Gilbert-type fan deltas developed on the northern edge of the basin. These sedimentary structures are separated from reefal carbonates and the Reef Unit by the Messinian Erosional Surface (MES). The various facies of the Sorbas Member have been correlated with the bottomset beds of the Gilbert-type fan deltas despite some differences in palaeobathymetry. In the southeastern periphery of the basin, the MES separates the Sorbas Member from the Yesares gypsums. In the central part of the basin, a hiatus characterizes the contact between these members. The Zorreras Member postdates the MSC and entirely belongs to Zanclean. Its white >Lago Mare> layers are lagoonal deposits, the fauna of which is confirmed to result from Mediterranean-Paratethys high sea-level exchange after the post-MSC marine reflooding of the Mediterranean Basin. This study allows to re-assert the two-step scenario of the MSC (Clauzon et al., 1996) with the following events: - at 5.971-5.600 Ma, minor sea-level fall resulting in the desiccation of this peripheral basin with secondary fluctuations;- at 5.600-5.460 Ma, significant subaerial erosion (or lack of sedimentation) caused by the almost complete desiccation of the Mediterranean Sea;- instantaneous marine reflooding, accepted at 5.460 Ma, followed by continuing sea-level rise. © 2015 Elsevier Ltd., For some of us, the beginning of this investigation has been funded by previous CNRS projects (RCP 826, Programme ECLIPSE), the recent field research has been supported by the Projects AMEDITER (“Actions Marges” CNRS/INSU Programme), “Bassins néogènes et manteau en Méditerranée” (TerMEx CNRS/INSU Programme), the CIFRE PhD grant Nº 584/2010 (TOTAL/UPMC) and the Research Project CGL2010-15047 (Spanish Government)