Evidence for forearc seafloor-spreading from the Betts Cove ophiolite, Newfoundland: oceanic crust of boninitic affinity

• Published in: Tectonophysics Vol. 284; no. 3-4; pp. 233 - 245
• Main Authors: Bédard, J.H., Lauzière, K., Tremblay, A., Sangster, A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 30.01.1998
• Subjects: Betts Cove; Bonin Islands; boninite; extension; Marine; ophiolite; seafloor-spreading; Canada, Newfoundland, Betts Cove Ophiolite; ophiolite; Betts Cove; extension; seafloor-spreading; boninite; Bonin Islands
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/S0040-1951(97)00182-0

The Ordovician Betts Cove ophiolite of Newfoundland has a well-developed cumulate sequence, in which is rooted a sheeted dyke complex that grades up into pillow lavas. Dominant chromite + olivine + orthopyroxene cumulate peridotites and orthopyroxenites have phase assemblages and mineral chemistries consistent with crystallization from boninitic magmas. Dykes and lavas have phenocrysts of olivine + high-CrAl chromite ± orthopyroxene ± low-TiO2 clinopyroxene. They have high SiO2 and MgO contents, and depleted U-shaped trace-element profiles indistinguishable from those of Bonin Islands boninites. Field data imply that cumulates, dykes and lavas all are comagmatic, while geochemical and mineralogical data indicate that all are of boninitic affinity. Since boninites are only found in forearcs, this implies that the Betts Cove ophiolitic crust formed in a forearc. Since the entire oceanic crustal section at Betts Cove is of boninitic affinity, then this implies that true seafloor-spreading can initiate in forearc.