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An evaluation of Mesozoic rift-related magmatism on the margins of the Labrador Sea: Implications for rifting and passive margin asymmetry

Peace, Alexander; McCaffrey, Ken; Imber, Jonathan; Phethean, Jordan; Nowell, Geoff; Gerdes, Keith; Dempsey, Edward


Alexander Peace

Ken McCaffrey

Jonathan Imber

Jordan Phethean

Geoff Nowell

Keith Gerdes

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Dr Eddie Dempsey
Lecturer in Structural Geology, Programme Director (Geology and GPG)


The Labrador Sea is a small (∼900 km wide) ocean basin separating southwest Greenland from Labrador, Canada. It opened following a series of rifting events that began as early as the Late Triassic or Jurassic, culminating in a brief period of seafloor spreading commencing by polarity chron 27 (C27; Danian) and ending by C13 (Eocene-Oligocene boundary). Rift-related magmatism has been documented on both conjugate margins of the Labrador Sea. In southwest Greenland this magmatism formed a major coast-parallel dike swarm as well as other smaller dikes and intrusions. Evidence for rift-related magmatism on the conjugate Labrador margin is limited to igneous lithologies found in deep offshore exploration wells, mostly belonging to the Alexis Formation, along with a postulated Early Cretaceous nephelinite dike swarm (ca. 142 Ma) that crops out onshore, near Makkovik, Labrador. Our field observations of this Early Cretaceous nephelinite suite lead us to conclude that the early rift-related magmatism exposed around Makkovik is volumetrically and spatially limited compared to the contemporaneous magmatism on the conjugate southwest Greenland margin. This asymmetry in the spatial extent of the exposed onshore magmatism is consistent with other observations of asymmetry between the conjugate margins of the Labrador Sea, including the total sediment thickness in offshore basins, the crustal structure, and the bathymetric profile of the shelf width. We propose that the magmatic and structural asymmetry observed between these two conjugate margins is consistent with an early rifting phase dominated by simple shear rather than pure shear deformation. In such a setting Labrador would be the lower plate margin to the southwest Greenland upper plate.

Journal Article Type Article
Publication Date Dec 1, 2016
Journal Geosphere
Print ISSN 1553-040X
Electronic ISSN 1553-040X
Publisher Geological Society of America
Peer Reviewed Peer Reviewed
Volume 12
Issue 6
Pages 1701-1724
APA6 Citation Peace, A., McCaffrey, K., Imber, J., Phethean, J., Nowell, G., Gerdes, K., & Dempsey, E. (2016). An evaluation of Mesozoic rift-related magmatism on the margins of the Labrador Sea: Implications for rifting and passive margin asymmetry. Geosphere, 12(6), 1701-1724. doi:10.1130/GES01341.1
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