The Noggin Cove formation and Carmanville melange: island arc rifting in northeast Newfoundland

Johnston, Dennis Hugh (1992) The Noggin Cove formation and Carmanville melange: island arc rifting in northeast Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Noggin Cove Formation consists mainly of fragmental mafic volcanic rocks with subordinate pillowed basalt and black shale. Massive volcanic conglomerates and coarse sandstones, with lesser amounts of medium-bedded tuffs and lapilli breccias, dominate the fragmental rocks. Volcanic conglomerates and coarse-grained sandstones were predominantly deposited as subaqueous debris flows, some of which are spectacular in terms of their thickness and clast size. -- The volume of fragmental rocks relative to basaltic lavas indicates an explosive volcanic source; ubiquitous vesicular clasts indicate shallow marine to subareal eruption. Debris flow conglomerates and sandstones dominate southern exposures but in the north they are subordinate to basaltic lavas and shallow marine deposits (highly calcareous tuffs and breccias). This distribution implies fragmental rocks were transported southward to form a marine volcaniclastic apron over pillow lavas, lava flows and basaltic dykes. -- The Carmanville Melange consists mainly of sandstone, siltstone and mafic volcanic clasts and blocks in a black shale matrix. Melange is interbedded and interfolded with volcanic rocks of the underlying Noggin Cove Formation and with siltstones and sandstones of the overlying Woody Island Siltstone. In many cases, folded beds of siltstone can be seen within the black shale matrix. The melange is interpreted as olistostromal. -- The Noggin Cove Formation and Carmanville Melange have undergone at least three stages of folding. D₂ deformation is the most intense, resulting in a very strong northeast trending cleavage which is axial planar to tight to isoclinal folds. Microprobe, SEM and textural analyses show that greenschist facies metamorphism and subsequent contact metamorphism have extensively altered the volcanic rocks of the Noggin Cove Formation. -- Rifting is indicated by the debris flows of the Noggin Cove Formation and by olistostromes of the Carmanville Melange and Woody Island Siltstone. An arc to back-arc geochemical transition matches the stratigraphic record of rifting. The arc to back-arc succession is correlated with the Exploits and Wild Bight groups of the western Exploits Subzone.

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