Geology and geochemistry of an alkali volcanic suite (Skinner Cove Formation) in the Humber Arm Allochthon, Newfoundland

Baker, Donald Frederick (1979) Geology and geochemistry of an alkali volcanic suite (Skinner Cove Formation) in the Humber Arm Allochthon, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Skinner Cove Formation, an igneous/metamorphic assemblage, comprises one of a number of transported slices in the Humber Arm Allochthon of western Newfoundland. The allochthon was assembled in an Ordovician ocean basin and at a continental margin, and then emplaced upon platform carbonates of the continental shelf during the lower Middle Ordovician. The Skinner Cove Formation, presently recognized only in the northern part of the allochthon, consists of two structural slices (Trout River and Chimney Cove). Two other slices, containing rocks previously included in the Skinner Cove, are herein named the Western Head and Beverley Head slices; rocks of the former slice are assigned to the Little Port Complex, and those of the latter to a miscellaneous structural unit. These four slices are everywhere structurally separate, one from another. Additionally, each of the four newly named slices is overlain structurally by other slices of either the Little Port Complex or the Bay of Islands (ophiolite) Complex, and is underlain structurally by sedimentary slices of the Humber Arm Supergroup. Locally, Skinner Cove rocks are enveloped in mélange and structurally associated with sediments of the Humber Arm Supergroup. -- The Skinner Cove Formation is typified by the stratigraphy and lithologies in the Trout River slice. Rocks of the Trout River slice are herein subdivided into the Main Sea Stack, Wallace Brook and Red Fire Brook Members, which consist of a distinctive, undeformed lithic assemblage including mafic and intermediate lavas, trachyte, subvolcanic rocks and volcaniclastics. These have all been altered to a metamorphic mineral assemblage, zeolite/analcime-quartz, which is diagnostic of zeolite facies metamorphism. The Chimney Cove slice is composed mainly of epiclastic breccia and fossiliferous limestone, with brecciated mafic lavas similar to those in the Trout River slice. Rocks of the Beverley Head slice are internally imbricated, with rocks of the Little Port Complex, Humber Arm Supergroup and Skinner Cove Formation all represented. -- Mineralogical, petrochemical and petrographic studies show that the Skinner Cove is a differentiated, mildly alkaline igneous suite (presently metamorphosed to zeolite facies) that underwent olivine and clinopyroxene fractionation. In contrast, the mafic rocks of the Little Port are texturally, mineralogically and petrochemically distinct from the Skinner Cove suite. There is no apparent direct genetic relationship between the rocks of the Skinner Cove Formation and the rocks in any other allochthonous assemblage (e.g. Little Port Complex). -- Prior to its incorporation into the allochthon, the Skinner Cove Formation is interpreted to have been a mature oceanic volcano that erupted alkaline magma. T^e Little Port Complex, which has subalkaline magmatic affinities, is interpreted to include both ocean floor volcanics and volcanic arc rocks.

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