The Betts Cove ophiolite and related rocks of the Snooks Arm group, Newfoundland

Upadhyay, Hansa Datt (1973) The Betts Cove ophiolite and related rocks of the Snooks Arm group, Newfoundland. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The Snooks Arm Group consists of a Lower Ordovician ophiolite suite at the base which is conformably overlain by two sedimentary/pyroclastic and two pillow lava formations. The ophiolite suite, best developed at Betts Cove, comprises a basal ultramafic member followed in order by a gabbroic, a sheeted dyke, and a pillow lava member, all of which have transitional contacts with each other. The ultramafic member consists of interlayered peridotite, pyroxenite, serpentinized dunite, and minor rodingitized gabbro. The gabbroic member consists of layered quartz gabbro, minor clinopyroxenite and quantitatively negligible diorite. The sheeted dyke member possesses over 90 percent diabase and ultramafic dykes that are subvertical and parallel to one another. The pillow lava member contains basaltic (spilitic) and ultramafic pillows and sills. The sedimentary/pyroclastic formations consist of andesitic agglomerate and flysch, deep-sea sediments and diabase sills. The two pillow lava formations of the upper part of the Snooks Arm Group comprise tholeiitic basalt and diabase dykes/sills that were derived from a different magma group. -- The Betts Cove ophiolite is interpreted as part of a Lower Ordovician oceanic crust and mantle that was developed through sea-floor spreading and was subsequently thrust (obducted) on to the Fleur de Lys continental mass. Field and chemical data indicate that the ophiolite suite was produced through fractional crystallization of a single parent magma with a hiatus between the formation of the ultramafic-gabbro sequence and that of the sheeted dyke-pillow lava assemblage. The upper part of the Snooks Arm Group shows affinity to an island arc type environment and might represent crust of a basin marginal to a major Lower Paleozoic ("Proto-Atlantic") ocean. -- The Snooks Arm Group was subjected to low-grade burial metamorphism during Early Ordovician and to greenschist facies regional metamorphism during Devonian (Acadian) time. -- The ophiolite suite is similar in many respects to the modern oceanic crust and to ophiolites elsewhere. The origin and tectonic evolution of the Snooks Arm Group is described in terms of a plate tectonic model related to the opening and closing of an ancient ocean. -- Copper mineralization in Betts Cove area is concentrated at the contact of sheeted dykes and pillow lavas and is interpreted as co-magmatic with the mafic host rocks. Models are proposed for the magmatism and metallogeny of Betts Cove ophiolite that may help understanding of some of the processes operative on modern ocean floors.

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