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Two wide-angle seismic reflection/refraction profiles were acquired to determine the velocity characteristics of the Meguma terrane and adjacent Avalonia northeast of the Cobequid-Chedabucto Fault Zone (CCFZ) in eastern Canada. Line 99–1 is located along the Scotian margin whereas line 99–2 crosses the Scotian margin and onshore Nova Scotia and extends into the Gulf of St. Lawrence. Velocity models were derived by forward modelling of travel times. P-wave velocities of 5.5–6.0 km/s and 6.0–6.4 km/s are interpreted to be metasedimentary rocks of the Goldenville and Halifax groups and granitic rocks, respectively. This inference is based on comparison with laboratory velocities of a suite of rock samples, offshore sampling, links to onshore geology with multibeam bathymetry, and gravity modelling. On both lines a low velocity zone (LVZ) >350 km wide and up to 15 km thick is present at mid-crustal levels. The LVZ is not observed beneath onshore Nova Scotia or northeast of Orpheus Graben, the offshore extension of the CCFZ. The crustal thickness of the Meguma terrane varies between 31 and 38 km; in contrast, the Moho is at a depth of 41 km beneath Avalonia. The velocity of the lower crust on line 99–2 is 6.8–7.1 km/s beneath the LVZ and Avalonia, and 6.6 km/s beneath onshore Meguma terrane. Poisson's ratios calculated from P- and S-wave velocities are 0.19–0.23 in the Meguma terrane crust; in contrast, Poisson's ratios of 0.24–0.25 are indicated for Avalonian crust. • Seismic reflection/refraction, gravity, and rock density/velocity data were obtained. • Two velocity/depth models were generated onshore and offshore of Nova Scotia, Canada. • Both models show an extensive low-velocity zone in the offshore Meguma terrane. • Meguma terrane has crustal structure different from that of adjacent Avalonia. • Avalonia extends only 30 km under Meguma terrane in faulted contact. [ABSTRACT FROM AUTHOR]

The Alpha Ridge-Mendeleev Rise (AMR) is the major bathymetric feature in the Amerasia Basin of the Arctic Ocean. Its tectonic history is controversial due to its remote location in ice covered waters making data acquisition difficult, resulting in the lack of diagnostic data. Analysis of the wide-angle reflection/refraction data based on the compressional waves (P-waves) from the AMR indicates that its velocity/depth structure is typical of large igneous provinces (LIPs). LIPs can form on either oceanic or continental crust and can exhibit complex history of development. Here converted shear waves (S-wave) on the Alpha Ridge have been used to calculate Poisson's ratios and many of measured values are within the felsic range in the upper crust. They are comparable to published S-waves from the Mendeleev Rise. They are also consistent with the results of Rayleigh-wave group-velocity analysis that indicate the Alpha Ridge in adjacent northern Canada has an intermediate composition. Based on magnetics, pseudogravity and volumetric considerations the High Arctic Large Igneous Province (HALIP) most closely resembles the Kerguelen Plateau, a LIP with a continental component. The geophysical characteristics of the AMR are compatible with a number of other LIPs that have continental affinities. A variety of offshore information from dredges and cores and onshore geological data support continental fragments incorporated in the AMR. [ABSTRACT FROM AUTHOR]

Canada ratified the United Nations Convention on the Law of the Sea (UNCLOS) in 2003. With that ratification is an obligation to submit data and information to the U.N. pertaining to the limits of the country's extended continental shelf (ECS); the portion of the juridical continental shelf that extends beyond 200 nautical miles. A team of Canadian scientists, managers, and legal experts that included representation from three Federal Departments (Natural Resources Canada, Fisheries and Oceans Canada, and Global Affairs Canada) with additional support from other departments, spent 13 years compiling and acquiring data to provide the scientific evidence to support delineation of Canada's seaward most maritime limit. The submission has the potential to provide Canada with 2.4 million km2 of additional submarine landmass in the Atlantic and the Arctic oceans over which Canada exercises sovereign rights for the purpose of exploring and exploiting its natural resources. Specific information such as the tectonic framework of the continental margin, the geomorphology of the margin and in particular the continental slope, the geologic nature of adjoined ridges, rises, and plateaux, and sediment thickness within adjacent basins are examples of fundamental pieces of geoscientific information needed to substantiate Canada's outermost maritime limits. This paper highlights a number of segments of Canada's continental margins to showcase this scientific evidence and how it is applied in the UNCLOS context. In doing so, the paper demonstrates the geologic complexity of Canada's margins as illustrated in scientific publications that have resulted from these new data collections, while at the same time presenting new scientific evidence and interpretations. This collection of data and information provides a wealth of new knowledge in Canada's offshore regions. The massive data compilation in the Atlantic led to conception of continental margins, in a source-to-sink scenario, as having an equilibrium base level or graded form, comparable to river systems. Departures from this shape relate to the interplay of sedimentary processes and in particular to those processes that do not fit the source-to-sink paradigm. For example, a significant part of the Atlantic margin is shown to be heavily influenced by along-slope geostrophic currents that generated massive contourite drift deposits. These deposits reflect lateral transport of sediment that had a significant impact on the morphology of the margin. The role of mass transport processes in shaping continental margins is also highlighted, and in particular the collapses of entire segments of the margin were observed. The prominent role mass failure processes play in delivering sediment to the adjacent abyssal plain is also critical in the ECS context. These observations challenge the entrenched notion of a continental margin comprising a shelf, slope, and rise and in particular the concept of the "continental rise". Prior to 2006, regions of the Arctic Ocean seaward of the Canadian landmass had fewer than 5000 km of seismic reflection data. The massive efforts of Arctic coastal States to map their margins for ECS purposes have led to a leap in technological advances to acquire data in ice-covered seas and have led to a wealth of new geoscientific knowledge. Perhaps foremost amongst this knowledge is demonstration that Canada Basin is indeed a fully developed ocean basin, albeit significantly infilled with sediment. Based on this knowledge and identification of related structures, new realistic tectonic scenarios for opening of the Amerasia Basin are proposed that include a significant component of transform or strike-slip motions. With seismic velocity and rock sample information, the continental nature of Alpha and Mendeleev ridges has been substantiated. Even bathymetric data were lacking in the Arctic and new editions of seafloor maps now support grids of 500 m spacing; although some regions remain sparse. Once thought to be relatively stagnant, sedimentary processes such as found in many ocean basins were discovered in the Arctic Ocean. Evidence of geostrophic currents, sediment mass failures, and deep-sea turbidity current channels were found to be ubiquitous, even in the deepest parts of the Arctic's basins. [ABSTRACT FROM AUTHOR]

• Gravity-derived basement topography constraint on the Canada Basin spreading system. • Consistent oblique ridge sub-segmentation along northeast-trending non-transforms. • Highly oblique sea-floor spreading in the Canada Basin during the Early Cretaceous. • Termination of seafloor spreading during a geomagnetic reverse polarity chron. • Juxtaposition of Chuckchi Borderland and Sever Spur prior to ocean crust formation. Understanding the evolution of ocean basins is critical for studies in global plate tectonics, mantle dynamics, and sea-level through time, and relies on identifiable tectonic plate boundaries. The evolution of the 2.5 million km2 Amerasia Basin in the Arctic Ocean remains largely unsettled due to widespread overprint by the Cretaceous High-Arctic Large Igneous Province. Traces of an extinct, but deeply buried, spreading centre (herein South Amerasia Ridge, SAR) has been shown to exist in the southern part of the Amerasia Basin, in the Canada Basin. However, structural details of the SAR and, hence, the kinematic evolution of the Canada Basin, are yet to be unraveled. Based on 3D gravity inversion and the vertical gravity gradient of the latest generation of satellite gravity models, we document new structures within the Canada Basin spreading system. Our results are supported by analysis of aeromagnetic and recent marine geophysical data. Evidence is shown of consistent oblique segmentation of the SAR spreading centre in a right stepping en echelon pattern. The spreading segments are offset by northeast-trending non-transforms that are traceable throughout the oceanic crustal domain and parallel to pre-oceanic strike-slip faults in the older part of the Canada Basin. We interpret the SAR to have formed by highly oblique spreading in a northeast-southwest direction. We compare the predicted SAR basement topography with the global ridge systems and produce a detailed magnetic modelling also constrained by the basement topography. The results indicate that the SAR crust formed by a slow-to-intermediate spreading regime and that sea-floor spreading terminated during a reverse polarity chron, most likely in the Early Cretaceous. Our novel plate reconstruction model, adopting a highly oblique spreading in Canada Basin, requires a translational motion of the Alaska/Chukotka tectonic block, replacing the decades-old rotational model of the Cretaceous High Arctic. [ABSTRACT FROM AUTHOR]