Aline Rabain

Bio: Aline Rabain is an academic researcher from Institut de Physique du Globe de Paris. The author has contributed to research in topics: Mid-Atlantic Ridge & Lava. The author has an hindex of 2, co-authored 2 publications receiving 277 citations.

Crustal thickness of V‐shaped ridges south of the Azores: Interaction of the Mid‐Atlantic Ridge (36°–39°N) and the Azores hot spot

Abstract: V-shaped ridges propagating along the Mid-Atlantic Ridge axis south of the Azores and Iceland hot spots indicate that ridge-hot spot interactions produce temporal and spatial variations in melt supply to the ridge axis. Estimates of relative crustal thickness variations associated with the ridges south of the Azores hot spots, based on gravity and bathymetry data collected during the SudAcores cruise (1998), provide constraints on the rate of propagation of these melt anomalies and on the variations in melt production along the axis and in time. The maximum apparent crustal thickness along the Azores V ridge is ∼14 km near the Azores, decreasing to normal crustal thickness of ∼6 km toward the south. This crustal thickness variation may be explained by enhanced melt production associated with the propagation of a mantle temperature anomaly that initiated ∼10 Myr ago at the Azores hot spot. The temperature anomaly decreased as it propagated southward, reaching ambient mantle temperatures at the present time at its predicted location under the axis. The excess melt was emplaced on axis forming discrete, shallow (<1000 m) oceanic plateaus (∼100 km in diameter at ∼37.5°N) that are isostatically compensated. The numerous seamounts, lack of normal faults, and smooth basement at the summit of these plateaus suggest high effusion rates that persisted for ∼5 Myr or less, with little or no tectonic strain. As the melt anomaly propagated along axis, the magmatic activity at the plateaus ceased, resulting in rifting of the plateau and onset of normal seafloor spreading. The variations in crustal thickness inferred for the V ridges south of the Azores are at least twice that inferred for the Iceland structures. In both cases the V ridges record temporal variations in temperature and/or mantle flux that affect melt production under the ridge axis, but the fluctuations are larger for the Azores than for the Iceland hot spot.

Offshore Wind Integrated Geoscience Approach Considering Regulatory Requirements and Project Design Essentials to Optimize Timelines Bringing Value to Project, Developer, and Consumer

Abstract: Atlantic Shores Offshore Wind is developing one of the largest offshore wind energy projects along the U.S. East Coast. Given the large lease area covering 741 km2 and with minimal pre-existing geophysical, geotechnical, environmental, and marine archaeological data availability when the lease was awarded, significant front-end efforts were required to complete project design and regulatory site characterization. Collection of the information needed to progress the Construction Operations Plan and develop a project's detailed design parameters would typically take up to 4 years to finalize. This long duration is exacerbated by the misaligned timing of geophysical information needed early for permitting purposes compared to detailed geotechnical information acquired later, when project design essentials are better defined. This timing issue was managed through innovative phasing and integration of geoscience efforts in the first few years of the development. Coordinated acquisition of geohazards, geophysics, marine archaeology, geotechnics, and benthic habitat data, designed to cover the range of project variables within the project design envelope, optimized the survey campaign and resulted in a future-proof site characterization baseline. This case study highlights various technological, operational and strategic innovations implemented in the following areas: fisheries management and simultaneous vessel operations (SIMOPS), survey line planning, environmental and benthic planning, geotechnical tools and techniques, phased ground model development, data quality assurance and control, offshore operations oversight, data management and regulatory strategies. Refinement to survey plans, including orientation, sequencing, clustering, and multi-purposing data acquisition, delivered multiple efficiencies as the project matured. The team achieved geoscience data quality objectives and reduced survey durations by carefully considering commercial fishing intensity, metocean conditions, geological features, and survey line design or layout. Close coordination with multiple technical package teams was necessary to understand and anticipate evolving engineering data needs and minimize duplicate data gathering. This integrated approach enabled the project to accelerate the identification and interpretation efforts needed to answer critical questions for geotechnical ground modeling, archaeological paleolandscape modeling, geologic history determination, and benthic habitat mapping in ways that are unique and innovative to the offshore wind industry. The unprecedented use of new data displays and innovative mapping tools allowed various project development and engineering design experts from across the global project team to easily access the wealth of geoscientific information developed without the need for specialty software or extensive training. The approach also realized valuable benefits in the areas of offshore safety, achieving critical milestones, and supporting Atlantic Shores Offshore Wind goals of environmental stewardship, being a good neighbor and leading with science.

Geologically current plate motions

Abstract: SUMMARY We describe best-fitting angular velocities and MORVEL, a new closure-enforced set of angular velocities for the geologically current motions of 25 tectonic plates that collectively occupy 97 per cent of Earth's surface. Seafloor spreading rates and fault azimuths are used to determine the motions of 19 plates bordered by mid-ocean ridges, including all the major plates. Six smaller plates with little or no connection to the mid-ocean ridges are linked to MORVEL with GPS station velocities and azimuthal data. By design, almost no kinematic information is exchanged between the geologically determined and geodetically constrained subsets of the global circuit—MORVEL thus averages motion over geological intervals for all the major plates. Plate geometry changes relative to NUVEL-1A include the incorporation of Nubia, Lwandle and Somalia plates for the former Africa plate, Capricorn, Australia and Macquarie plates for the former Australia plate, and Sur and South America plates for the former South America plate. MORVEL also includes Amur, Philippine Sea, Sundaland and Yangtze plates, making it more useful than NUVEL-1A for studies of deformation in Asia and the western Pacific. Seafloor spreading rates are estimated over the past 0.78 Myr for intermediate and fast spreading centres and since 3.16 Ma for slow and ultraslow spreading centres. Rates are adjusted downward by 0.6–2.6 mm yr−1 to compensate for the several kilometre width of magnetic reversal zones. Nearly all the NUVEL-1A angular velocities differ significantly from the MORVEL angular velocities. The many new data, revised plate geometries, and correction for outward displacement thus significantly modify our knowledge of geologically current plate motions. MORVEL indicates significantly slower 0.78-Myr-average motion across the Nazca–Antarctic and Nazca–Pacific boundaries than does NUVEL-1A, consistent with a progressive slowdown in the eastward component of Nazca plate motion since 3.16 Ma. It also indicates that motions across the Caribbean–North America and Caribbean–South America plate boundaries are twice as fast as given by NUVEL-1A. Summed, least-squares differences between angular velocities estimated from GPS and those for MORVEL, NUVEL-1 and NUVEL-1A are, respectively, 260 per cent larger for NUVEL-1 and 50 per cent larger for NUVEL-1A than for MORVEL, suggesting that MORVEL more accurately describes historically current plate motions. Significant differences between geological and GPS estimates of Nazca plate motion and Arabia–Eurasia and India–Eurasia motion are reduced but not eliminated when using MORVEL instead of NUVEL-1A, possibly indicating that changes have occurred in those plate motions since 3.16 Ma. The MORVEL and GPS estimates of Pacific–North America plate motion in western North America differ by only 2.6 ± 1.7 mm yr−1, ≈25 per cent smaller than for NUVEL-1A. The remaining difference for this plate pair, assuming there are no unrecognized systematic errors and no measurable change in Pacific–North America motion over the past 1–3 Myr, indicates deformation of one or more plates in the global circuit. Tests for closure of six three-plate circuits indicate that two, Pacific–Cocos–Nazca and Sur–Nubia–Antarctic, fail closure, with respective linear velocities of non-closure of 14 ± 5 and 3 ± 1 mm yr−1 (95 per cent confidence limits) at their triple junctions. We conclude that the rigid plate approximation continues to be tremendously useful, but—absent any unrecognized systematic errors—the plates deform measurably, possibly by thermal contraction and wide plate boundaries with deformation rates near or beneath the level of noise in plate kinematic data.

The mean composition of ocean ridge basalts

Abstract: [1] The mean composition of mid-ocean ridge basalts (MORB) is determined using a global data set of major elements, trace elements, and isotopes compiled from new and previously published data. A global catalog of 771 ridge segments, including their mean depth, length, and spreading rate enables calculation of average compositions for each segment. Segment averages allow weighting by segment length and spreading rate and reduce the bias introduced by uneven sampling. A bootstrapping statistical technique provides rigorous error estimates. Based on the characteristics of the data, we suggest a revised nomenclature for MORB. “ALL MORB” is the total composition of the crust apart from back-arc basins, N-MORB the most likely basalt composition encountered along the ridge >500 km from hot spots, and D-MORB the depleted end-member. ALL MORB and N-MORB are substantially more enriched than early estimates of normal ridge basalts. The mean composition of back-arc spreading centers requires higher extents of melting and greater concentrations of fluid-mobile elements, reflecting the influence of water on back-arc petrogenesis. The average data permit a re-evaluation of several problems of global geochemistry. The K/U ratio reported here (12,340 ± 840) is in accord with previous estimates, much lower than the estimate of Arevalo et al. (2009). The low Sm/Nd and 143Nd/144Nd ratio of all morb and N-MORB provide constraints on the hypothesis that Earth has a non-chondritic primitive mantle. Either Earth is chondritic in Sm/Nd and the hypothesis is incorrect or MORB preferentially sample an enriched reservoir, requiring a large depleted reservoir in the deep mantle.

Digital isochrons of the world's ocean floor

Abstract: We have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self-consistent set of global isochrons and associated plate reconstruction poles. The age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading. Ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models. We have constructed an age grid with error estimates for each grid cell as a function of (1) the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid, (2) the distance of a given grid cell to the nearest magnetic anomaly identification, and (3) the gradient of the age grid: i.e., larger errors are associated with high age gradients at fracture zones or other age discontinuities. Future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere, the heat loss of the Earth, ridge-push forces through time, asymmetry of spreading, and providing constraints for seismic tomography and mantle convection models.

Evolution and Biogeography of Deep-Sea Vent and Seep Invertebrates

Abstract: Deep-sea hydrothermal vents and cold seeps are submarine springs where nutrient-rich fluids emanate from the sea floor. Vent and seep ecosystems occur in a variety of geological settings throughout the global ocean and support food webs based on chemoautotrophic primary production. Most vent and seep invertebrates arrive at suitable habitats as larvae dispersed by deep-ocean currents. The recent evolution of many vent and seep invertebrate species (<100 million years ago) suggests that Cenozoic tectonic history and oceanic circulation patterns have been important in defining contemporary biogeographic patterns.

Discovery of a magma chamber and faults beneath a Mid-Atlantic Ridge hydrothermal field

Abstract: Crust at slow-spreading ridges is formed by a combination of magmatic and tectonic processes, with magmatic accretion possibly involving short-lived crustal magma chambers The reflections of seismic waves from crustal magma chambers have been observed beneath intermediate and fast-spreading centres, but it has been difficult to image such magma chambers beneath slow-spreading centres, owing to rough seafloor topography and associated seafloor scattering In the absence of any images of magma chambers or of subsurface near-axis faults, it has been difficult to characterize the interplay of magmatic and tectonic processes in crustal accretion and hydrothermal circulation at slow-spreading ridges Here we report the presence of a crustal magma chamber beneath the slow-spreading Lucky Strike segment of the Mid-Atlantic Ridge The reflection from the top of the magma chamber, centred beneath the Lucky Strike volcano and hydrothermal field, is approximately 3 km beneath the sea floor, 3-4 km wide and extends up to 7 km along-axis We suggest that this magma chamber provides the heat for the active hydrothermal vent field above it We also observe axial valley bounding faults that seem to penetrate down to the magma chamber depth as well as a set of inward-dipping faults cutting through the volcanic edifice, suggesting continuous interactions between tectonic and magmatic processes