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TitleCrustal structure and magmatism of the Marvin Spur and northern Alpha Ridge, Arctic Ocean
AuthorFunck, T; Shimeld, J
SourceGeophysical Journal International vol. 233, 2022 p. 740-768,
Alt SeriesNatural Resources Canada, Contribution Series 20220027
PublisherRoyal Astronomical Society
MeetingChapman Conference on Large-scale Volcanism in the Arctic: The Role of the Mantle and Tectonics; Selfoss; IS; October 13-18, 2019
Mediaon-line; digital
File formathtml; pdf
ProvinceNunavut; Northern offshore region
AreaArctic Ocean
Lat/Long WENS-120.0000 -30.0000 89.0000 86.0000
Subjectstectonics; marine geology; geophysics; Science and Technology; Nature and Environment; geophysical surveys; seismic surveys, marine; tectonic history; magmatism; intrusions; models; continental margins; crustal structure; gravity anomalies; Alpha Ridge; Lomonosov Ridge; Marvin Spur; Fedotov Seamount; Mendeleev Rise; High Arctic Large Igneous Province (HALIP)
Illustrationslocation maps; seismic profiles; tables; gravity profiles
ProgramDelineating Canada's Continental Shelf Under UNCLOS
Released2022 12 12
The Marvin Spur is a 450-km-long east-west trending escarpment along the northernmost periphery of the Alpha Ridge, starting about 500 km from the coasts of Ellesmere Island and Greenland off the Arctic Ocean margin of North America and running subparallel to the Amerasian margin of the continental Lomonosov Ridge. This regionwas investigated as part of the Canada-Sweden Polar Expedition in 2016, from which two seismic profiles are presented. The first is a 165-km-long line along the crest of theMarvin Spur. The second is a 221-km-long line extending southwestward from the spur to the northern flank of the Alpha Ridge within the Cretaceous High Arctic Large Igneous Province (HALIP). Multichannel seismic reflection data were acquired along both lines using a 100-m-long streamer, and the airgun shots were also recorded using 16 sonobuoys and 5 stations on the sea ice to calculate a velocity model for the crust from forward modelling of seismic traveltimes. The Marvin Spur profile reveals up to 1100 m of sedimentary rocks on top of a 1-km-thick series of basalts (4.5-5.1 km s-1). Upper and lower crust have velocities of 5.8-5.9 km s-1 and 6.2-6.3 km s-1, respectively, with the upper crust being 1-2 km thick compared to around 13 km for the lower crust. A wide-angle double seismic reflection manifests the top and base of a 6-km-thick lower crustal layer that we interpret as magmatic underplating beneath the continental crust of the Marvin Spur. We correlate a high-amplitude magnetic anomaly on Marvin Spur with a comparable anomaly on Lomonosov Ridge by invoking 110 km of dextral strike-slip motion. Assuming that HALIPrelated magmatic deposits generate these anomalies, the strike-slip motion pre-dates the main phase of magmatism (latest Cretaceous, 78 Ma). On the northern Alpha Ridge, sediments are around 1-km-thick and cover a 700 to 1700-m-thick series of basalts with velocities of 4.4-4.8 km s-1. Below is a 3-km-thick layer with intermediate velocities of 5.6 km s-1 and a lower crust with a velocity of 6.8 km s-1. Moho depth is not resolved seismically, but gravity modelling indicates a total thickness of 13 or 18 km for the igneous crust except for the Fedotov Seamount where Moho deepens by about 5 km. Construction of the seamount occurred in multiple magmatic phases, including flow eruptions during deposition of the Cenozoic sedimentary succession post-dating the main HALIP magmatism.
Summary(Plain Language Summary, not published)
The Marvin Spur is a 450-km-long, east-west trending seafloor escarpment in the Arctic Ocean, starting about 500 km from the coasts of Ellesmere Island and Greenland. It occurs along the northern periphery of the Alpha Ridge, subparallel to the Lomonosov Ridge that divides the Arctic Ocean into the Mesozoic-aged Amerasia Basin and the Cenozoic-aged Eurasia Basin. We present two new geophysical profiles of the Marvin Spur and northern Alpha Ridge. These profiles include seismic refraction, wide-angle reflection, short-offset reflection and gravimetric data collected during the Canada-Sweden Polar Expedition of 2016. They provide important information about the Earth's crust beneath the Amerasia Basin, and how that basin formed through time. The first profile follows the crest of the Marvin Spur for a distance of 165 km. From there, the second profile extends southwestward for a distance of 221 km across the northern flank of the Alpha Ridge, which is an offshore component of the Cretaceous-aged High Arctic Large Igneous Province (HALIP) identified in many onshore regions surrounding the Arctic Ocean. Crustal velocities along Marvin Spur are too low for igneous crust, supporting the hypothesis that it is a continental sliver rifted from the Lomonosov Ridge. The spur exhibits substantial magmatic overprinting likely related to the HALIP. We interpret that a 1 km-thick sequence of basalt flows forms the upper crust, and that magmatic underplating occurs beneath the base of the crust in this region. A different crustal structure occurs along the second profile crossing the northern Alpha Ridge. Here the uppermost crust includes an up to 2-km-thick series of volcanics, separated from the lower crust by a 3-km-thick layer of intermediate seismic velocity (5.6 km s-1). The total thickness of igneous crust, estimated by gravity modelling, is 13 km in the north near Marvin Spur, and 18 km in the south beneath Fedotov Seamount. The seamount is associated with volcanism that postdates the main HALIP magmatic phases, including interpreted sills that could be an interesting target for future scientific drilling since they occur at a depth of only 300 m beneath the seafloor.

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