Inversion of Taconian extensional structures during Paleozoic orogenesis in western Newfoundland

Abstract

West Newfoundland was critical in developing the Wilson Cycle concept. Neoproterozoic rifting established a passive margin adjacent to the Iapetus Ocean. Ordovician (Taconian) arc–continent collision emplaced ophiolites and the thin-skinned Humber Arm Allochthon. Subsequent Devonian (Acadian) ocean closure produced basement-cutting thrust faults that control the present-day distribution of units. New mapping, and aeromagnetic and seismic interpretation, around Parsons Pond enabled the recognition of structures in poorly exposed areas.Following Cambrian to Middle Ordovician passive-margin deposition, Taconian deformation produced a flexural bulge unconformity. Subsequent extensional faults shed localized conglomerate into the foreland basin. The Humber Arm Allochthon contains a series of stacked and folded duplexes, typical of thrust belts. To the east, the Parsons Pond Thrust has transported shelf and foreland-basin units c. 8 km westwards above the allochthon. The Long Range Thrust shows major topographical expression but <1 km offset. Stratigraphic relationships indicate that most thrusts originated as normal faults, active during Neoproterozoic rifting, and subsequently during Taconian flexure. Devonian continental collision inverted the Parsons Pond and Long Range thrusts. Basement-cored fault-propagation folds in Newfoundland are structurally analogous to basement uplifts in other orogens, including the Laramide Orogen in western USA. Similar deep-seated inversion structures may extend through the northern Appalachians.

Anticosti foreland basin offshore of western Newfoundland: Concealed record of northern Appalachian orogen development

“…Although we have not systematically identified the deeper reflections, subsidence analyses of the platform succession by Bond et al (1984) and Smith and Rasmussen (2008) indicate gradual, concave-up subsidence curves and subsidence rates <0.01 km/Myr consistent with thermal subsidence of a passive margin. We interpret these faults as having formed in the Laurentian margin at the onset of the Taconian Orogeny (Bradley & Kidd, 1991;White & Waldron, 2019). We interpret these offsets as faults with steep apparent dips (Figures 4 and 5).…”

“…The reflections in p are repeatedly offset in TWT, disrupting lateral continuity. Rarer reverse offsets probably record later inversion, similar to that which affected the Round Head and Parsons Pond thrusts on land (Waldron et al, 1993;White & Waldron, 2019). Offset is dominantly normal, but reverse faults also occur.…”

“…The tectonic wedge is in turn cut by the deepseated Round Head thrust that reactivated an earlier, Taconian extensional structure (Waldron, Stockmal, Corney, & Stenzel, 1993); folds associated with this structure are truncated unconformably by flat-lying Visean strata of the Maritimes Basin. Correlative basement-involved faults also reactivate earlier structures along the Parsons Pond Thrust in the Newfoundland Northern Peninsula (Figure 1b) (White & Waldron, 2019).…”

“…470 Ma: Waldron & van Staal, 2001). North of Bonne Bay (Figure 1b), the Humber Arm Allochthon displays structures typical of fold and thrust belts, such as stacked and folded duplexes (White & Waldron, 2019). North of Bonne Bay (Figure 1b), the Humber Arm Allochthon displays structures typical of fold and thrust belts, such as stacked and folded duplexes (White & Waldron, 2019).…”

“…Middle Ordovician extension on these faults played a role in generating accommodation for the earliest foredeep deposits (Lacombe, 2017;Palmer, Waldron, & Skilliter, 2002;Stockmal et al, 2004). White and Waldron (2019) interpret these structures as reactivated faults, originally related to Neoproterozoic to Cambrian opening of the Iapetus. White and Waldron (2019) interpret these structures as reactivated faults, originally related to Neoproterozoic to Cambrian opening of the Iapetus.…”