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TitleDepleted and ultradepleted basalt and picrite in the Davis Strait: Paleocene volcanism associated with a transform continental margin
AuthorLarsen, L M; Williamson, M -CORCID logo
SourceGeological Journal 2020 p. 1-21,
Alt SeriesNatural Resources Canada, Contribution Series 20190360
PublisherCambridge University Press
Mediapaper; on-line; digital
File formatpdf
ProvinceEastern offshore region; Nunavut
AreaDavis Strait; Labrador Sea; Baffin Bay
Lat/Long WENS -65.0000 -45.0000 72.0000 60.0000
Subjectsmarine geology; tectonics; structural geology; geochemistry; igneous and metamorphic petrology; geophysics; paleontology; Nature and Environment; Science and Technology; continental margins; plate margins; tectonic history; crustal studies; tectonic environments; rifting; sea floor spreading; magmatism; volcanism; thermal analyses; temperature; mantle; lithosphere; dredging; exploration wells; core samples; Paleogene; Paleocene; bedrock geology; lithology; igneous rocks; volcanic rocks; basalts; intrusive rocks; picrites; peridotites; structural features; faults; faults, extension; faults, transform; geophysical interpretations; biostratigraphy; fossil zones; micropaleontology; microfossils; crustal thickness; isotopic studies; Davis Strait High; Hekja O-71 Well; Gjoa G-37 Well; Nukik-2 Well; Hellefisk-1 Well; Dynocysts; Ungava Transform Zone; Phanerozoic; Cenozoic; Tertiary
Illustrationsgeoscientific sketch maps; lithologic logs; tables; variation diagrams; geochemical plots; geochemical profiles
Released2020 02 13
AbstractVolcanic rocks from the Davis Strait were studied to elucidate the tectonomagmatic processes during rifting and the start of seafloor spreading, and the formation of the Ungava transform zone between Canada and Greenland. The rocks are from the wells Hekja O-71, Gjoa G-37, Nukik-2 and Hellefisk-1, and from dredges on the northern Davis Strait High. Ages range from Danian to Thanetian (dinocyst palynozones P2 to P5, 62.5-57.2 Ma). The rocks are predominantly basaltic, but include picrites on the Davis Strait High. Calculated mantle potential temperatures for the Davis Strait High are c. 1500°C, suggesting the volume of magma generated was large; this is consistent with geophysical evidence for magmatic underplating in the region. The rare earth element patterns indicate residual mantle lithologies of spinel peridotite and, together with Sr-Nd isotopes, indicate melting beneath regionally extensive, depleted asthenosphere beneath a lithosphere of thickness similar to, or thinner than, beneath Baffin Island and distinctly thinner than beneath West Greenland. Some sites include basalts with more enriched compositions. Depleted and enriched basalts in the Hellefisk well show contemporaneous melting of depleted and enriched mantle components in the asthenosphere. The Hekja and Davis Strait High basalts and picrites have unique, ultradepleted compositions with (La/Sm)N < 0.5, (Tb/Lu)N < 1 and Nb/Zr = 0.013-0.027. We interpret these compositions as a product of the melting regime within the Ungava transform zone, where the melting column would be steep-sided in cross-section and not triangular as expected at normal spreading ridges. Magmatism along the transform stopped when the tectonic regime changed from transtension to transpression during earliest Eocene time.
Summary(Plain Language Summary, not published)
In this paper, we present the results of a collaborative geochemical study of igneous rocks recovered from drilling offshore in the Davis Strait. The rocks consist of basaltic and picritic lava flows of Paleocene age that were preserved on the West Greenland and Canadian continental margins during rift-related magmatism. This part of the conjugate margins has a complex tectonic history. The new geochemical data allow us to interpret the composition of basalts and picrites in terms of mantle processes associated with conjugate margin development.

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