Structural interpretation of the eastern Notre Dame Bay area, Newfoundland: regional post-Middle Silurian thrusting and asymmetrical folding

• Published in: Canadian Journal of Earth Sciences
• Main Authors: Karlstrom, K. E., Pluijm, B. A. van der, Williams, P. F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1982
• Subjects: Newfoundland
• Online Access: http://dx.doi.org/10.1139/e82-204; http://www.nrcresearchpress.com/doi/pdf/10.1139/e82-204

The structural geometry of the eastern Notre Dame Bay area is that of an allochthonous sequence (related to F 1 thrusting and folding), folded by F 2 asymmetrical folds, and offset by F 3 -related high-angle faults. F 1 folds are isoclinal and commonly intrafolial. F 2 folds are asymmetrical (generally tight) with axial surfaces that dip 30–85° southeast. The prominent northeast-striking, penetrative cleavage (S 2 ) is axial planar to F 2 folds. F 3 structures include chevron folds, box folds, kink bands, and local S 3 crenulation cleavage.F 1 folds are overprinted by F 2 folds producing coaxial and mushroom interference patterns. This and the subhorizontal enveloping surface of F 2 indicate that F 1 folds were recumbent prior to F 2 . A zone of F 1 folds separating Silurian turbidites from subaerial volcanics on the Port Albert Peninsula suggests F 1 was related to macroscopic thrusting, as does the association of F 1 with mesoscopic thrust faults.F 2 folds are the most obvious structures in the area. Macroscopic examples include an anticline–syncline pair on Milleners Peninsula; an anticlinorium cored by the Dunnage mélange, and a synclinorium cored by subaerial sandstones on the Port Albert Peninsula. These folds repeat the stratigraphy across areas that have been incorrectly interpreted in terms of fault-bounded, north-younging homoclines. A shallow enveloping surface for F 2 is supported by the uniformly low metamorphic grade in the area and detailed structural profiles. In view of the shallow dip of the enveloping surface, it is possible to correlate the Dunnage mélange, the Carman ville mélange, and other mélanges in the area.Contrary to prevailing interpretations of a structural setting involving fault-bounded tectonostratigraphic zones, we demonstrate a similar deformational history and a general continuity of macroscopic F 2 folds throughout our area. Rectilinear faults on geologic maps, used by previous workers as the boundaries between tectonostratigraphic zones, are post-F 2 features. They cross-cut ...