Evidence of Lithospheric Boudinage in the Grand Banks of Newfoundland from Geophysical Observations

Malcolm D J Macdougall,Alexander Braun,Georgia Fotopoulos

doi:10.3390/geosciences11020055

Abstract

The evolution of the passive margin off the coast of Eastern Canada has been characterized by a series of rifting episodes which caused widespread extension of the lithosphere and associated structural anomalies, some with the potential to be classified as a result of lithospheric boudinage. Crustal thinning of competent layers is often apparent in seismic sections, and deeper Moho undulations may appear as repeating elongated anomalies in gravity and magnetic surveys. By comparing the similar evolutions of the Grand Banks and the Norwegian Lofoten-Vesterålen passive margins, it is reasonable to explore the potential of the same structures being present. This investigation supplements our knowledge of analogous examples in the Norwegian Margin and the South China Sea with a thorough investigation of seismic, gravity and magnetic signatures, to determine that boudinage structures are evident in the context of the Grand Banks. Through analysis of geophysical data (including seismic, gravity and magnetic observations), a multi-stage boudinage mechanism is proposed, which is characterized by an upper crust short-wavelength deformation ranging from approximately 20–80 km and a lower crust long-wavelength deformation exceeding 200 km in length. In addition, the boudinage mechanism caused slightly different structures which are apparent in the block geometry and layeredness. Based on these results, there are indications that boudinage wavelength increases with each successive rifting phase, with geometry changing from domino style to a more shearband/symmetrical style as the scale of deformation is increased to include the entire lithosphere.

Highlights

Published: 28 January 2021The evolution of the Grand Banks region offshore of Newfoundland (Figure 1) dates back to the initiation of the breakup of the Pangea supercontinent approximately 200 Ma during the Late Triassic
Seismic, gravity and magnetic anomaly data obtained from the Geological Survey of Canada (GSC) [54,55,56] as well as a gravity anomaly map from [57]
We looked for direct evidence of boudinage structures by analyzing the undulations of interfaces such as the

Summary

Introduction

The evolution of the Grand Banks region offshore of Newfoundland (Figure 1) dates back to the initiation of the breakup of the Pangea supercontinent approximately 200 Ma during the Late Triassic. Through approximately 100 Ma of Mesozoic rifting, many of the resultant structures are preserved in the present-day strata [1,2,3,4,5]. There are differences in both the structural and stratigraphic character of the various sedimentary basins located in the Grand Banks, they are typically fault-bounded and separated by basement ridges [5]. Geophysical datasets—including 2D seismic, magnetic anomaly and free-air gravity anomaly—display some repetitive anomalous features both in geometry and material property that could be indicative of a boudinage mechanism impacting the tectonic evolution of the region.

Results

Discussion

Conclusion