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Two geophysical expeditions (LOMROG II and III) were carried out in 2009 and 2012 to acquire seismic data in the western Amundsen Basin in the Arctic Ocean, a basin formed by ultraslow seafloor spreading at the Gakkel Ridge. Previous studies show alternating magmatic and amagmatic segments at the ridge but it is unclear if such segmentation persisted throughout the entire opening history of the basin. The seismic refraction data were used to develop P -wave velocity models down to the uppermost mantle using forward modelling of traveltimes. The coincident seismic reflection data were used to constrain the geometry of the sedimentary layers and for characterizing the acoustic basement. 2-D gravity modelling was used to determine the Moho depth in areas when data quality was insufficient to resolve a Moho reflection. The models distinguish three different basement types: oceanic crust with layers 2 and 3, oceanic crust that is lacking a layer 3 and exhumed and serpentinized mantle. The maximum observed crustal thickness is 6 km. Areas with thin crust (<3 km) may be underlain by partially serpentinized mantle. Where exhumed mantle is observed, a serpentinization front separates highly serpentinized mantle at the top from partially serpentinized mantle below. The presence of oceanic crust off-axis of the presently amagmatic sector of the Gakkel Ridge indicates that there is both a spatial and temporal variation of crustal accretion processes at the ridge. [ABSTRACT FROM AUTHOR]

Abstract: Data from a refraction seismic profile parallel to the coast of Labrador (Canada) were used to determine the crustal structure across the boundary of the Nain and Makkovik provinces, [...]

Prestack depth-migrated seismic reflection data collected off Flemish Cap on the Newfoundland margin show a structure of abruptly thinning continental crust that leads into an oceanic accretion system. Within continental crust, there is no clear evidence for detachment surfaces analogous to the S reflection off the conjugate Galicia Bank margin, demonstrating a first-order asymmetry in final rift development. Anomalously thin (3-4 km), magmatically produced oceanic crust abuts very thin continental crust and is highly tectonized. This indicates that initial accretion of the oceanic crust was in a magma-limited setting similar to present-day ultraslow spreading environments. Seaward, oceanic crust thins to Keywords: continental margin, seafloor spreading, extension tectonics, continental breakup.

Orphan Basin, a massive deepwater rifted basin off the northeastern coast of Newfoundland, was one of the targets of the 2009 SIGNAL (Seismic Investigations off Greenland, Newfoundland and Labrador) experiment to collect refraction/wide-angle reflection (RWAR) data from the Bonavista Platform, through the Orphan Basin, to the Orphan Knoll, and beyond into oceanic crust. Both the data from an earlier RWAR acquisition and the new data were jointly analysed in order to improve on the earlier velocity model and extend its coverage landward and seaward. The resulting velocity model is characterized by an 8–9-km-thick sedimentary package immediately outboard of the Bonavista Platform, which thins toward the Orphan Knoll and beyond. The shallowest modelled sedimentary layer, interpreted as Paleocene and younger post-rift sediments, does not show significant thickness variations and velocities do not exceed 3.3 km s–1. The second modelled sedimentary layer with laterally variable velocities ranging from 2.3 to 5.3 km s–1, interpreted as Late Cretaceous post-rift sediments, is thickest over an interpreted failed rift. The deepest modelled sedimentary layer consists of laterally variable velocities that do not exceed 5.9 km s–1 and is interpreted as possibly Jurassic to Early Cretaceous syn-rift sediments. The crust beneath the Bonavista Platform is subdivided into an upper (5.4–5.9 km s–1), middle (5.9–6.4 km s–1) and lower crust (6.4–6.9 km s–1). The middle crust is modelled as disappearing beneath the seaward limit of the Bonavista Platform at an interpreted failed rift, only to re-appear 100 km further seaward beneath the central Orphan Basin and extend to the seaward limit of the Orphan Knoll, beyond which the crust can be modelled by just an upper (5.0–6.7 km s–1) and a lower (6.7–7.0 km s–1) crustal layer. Towards land, for the first 450 km of the model, velocities generally follow the globally averaged velocity trend for rifted continental crust, albeit with slightly elevated velocities suggestive of magmatic contributions. At the failed rift, within the continental domain, hyperextended crust is modelled, overlying a limited zone of serpentinized mantle. Seaward of Orphan Knoll, the interpretation for the velocity structure is less definitive but an 80-km-wide continent–ocean transition zone consisting of either transitional embryonic oceanic crust or thinned continental crust overlying serpentinized mantle is proposed. Upper mantle velocities as low as 7.7 km s–1 are modelled beneath the interpreted failed continental rift as well as beneath the continent–ocean transition zone, while the rest of the crustal model is underlain by typical mantle velocities of 8 km s–1. Analysis of extension and thinning factors based on the velocity model reveal that the failed rift experienced hyperextension and should have achieved full crustal embrittlement, consistent with localized mantle serpentinization. [ABSTRACT FROM AUTHOR]

Chronic pain patients present with cortical gray matter alterations, observed with anatomical magnetic resonance (MR) imaging. Reduced regional gray matter volumes are often interpreted to reflect neurodegeneration, but studies investigating the cellular origin of gray matter changes are lacking. We used multimodal imaging to compare 26 postmenopausal women with fibromyalgia with 25 healthy controls (age range: 50-75 years) to test whether regional gray matter volume decreases in chronic pain are associated with compromised neuronal integrity. Regional gray matter decreases were largely explained by T1 relaxation times in gray matter, a surrogate measure of water content, and not to any substantial degree by GABAA receptor concentration, an indirect marker of neuronal integrity measured with [18F] flumazenil PET. In addition, the MR spectroscopy marker of neuronal viability, N-acetylaspartate, did not differ between patients and controls. These findings suggest that decreased gray matter volumes are not explained by compromised neuronal integrity. Alternatively, a decrease in neuronal matter could be compensated for by an up regulation of GABAA receptors. The relation between regional gray matter and T1 relaxation times suggests decreased tissue water content underlying regional gray matter decreases. In contrast, regional gray matter increases were explained by GABAA receptor concentration in addition to T1 relaxation times, indicating perhaps increased neuronal matter or GABAA receptor up regulation and inflammatory edema. By providing information on the histological origins of cerebral gray matter alterations in fibromyalgia, this study advances the understanding of the neurobiology of chronic widespread pain. [ABSTRACT FROM AUTHOR]

The peri-infarct cortex (PIC) is the site of long-term physiologic changes after ischemic stroke. Traditional methods for delineating the peri-infarct gray matter (GM) have used a volumetric Euclidean distance metric to define its extent around the infarct. This metric has limitations in the case of cortical stroke, i.e., those where ischemia leads to infarction in the cortical GM, because the vascularization of the cerebral cortex follows the complex, folded topology of the cortical surface. Instead, we used a geodesic distance metric along the cortical surface to subdivide the PIC into equidistant rings emanating from the infarct border and compared this new approach to a Euclidean distance metric definition. This was done in 11 patients with [F-18]-Flumazenil ([18-F]-FMZ) positron emission tomography (PET) scans at 2 weeks post-stroke and at 6 month follow-up. FMZ is a PET radiotracer with specific binding to the alpha subunits of the type A γ-aminobutyric acid (GABAA) receptor. Additionally, we used partial-volume correction (PVC) of the PET images to compensate for potential cortical thinning and long-term neuronal loss in follow-up images. The difference in non-displaceable binding potential (BPND) between the stroke unaffected and affected hemispheres was 35% larger in the geodesic versus the Euclidean peri-infarct models in initial PET images and 48% larger in follow-up PET images. The inter-hemispheric BPND difference was approximately 17-20% larger after PVC when compared to uncorrected PET images. PET studies of peri-infarct GM in cortical strokes should use a geodesic model and include PVC as a preprocessing step. Hum Brain Mapp 38:326-338, 2017. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]