Structural Analysis and Kinematic Restoration along the Nova Scotia Passive Margin, Atlantic Canada
Creators: Berberoglu, Eren D.
Publisher: name: University of Alberta Library
Year: 2023

<p>The Nova Scotia passive continental margin is characterized by longitudinal variation in crustal structure from the volcanic U.S. Atlantic Margin in the southwest to a non-volcanic Newfoundland Margin in the northeast. The objectives of this study include characterizing the tectonic structure of the margin and analyzing the interconnected processes of extension, thermal subsidence, compaction, and isostatic response that contribute to the margin&#39;s tectonic evolution. In this study, 2D structural seismic interpretation integrated with published bathymetry, magnetic, and gravity surveys is carried out to characterize the tectonic structure of the margin. The 2D kinematic restorations along NW-SE cross-sections are conducted to quantify the variations in the amount of tectonic extension, subsidence, accommodation, isostatic response and compaction across and along the margin and compare how different crustal structural styles and salt kinematics affect these variations through time.<br>
Structural seismic interpretation reveal five sets of normal faults. (I) NE-SW-striking syn-rift planar normal faults are identified in the acoustic basement (J200) in the continental domain. (II) SE-dipping syn-rift listric normal faults in the basement merge into a flat detachment at ~15 km of depth in the oceanic domain. (IIIa) SE- and NW-dipping post-rift listric faults in the Cretaceous and Jurassic units merge into a basal detachment along the top of autochthonous salt within the northeastern and central shelf and slope. (IIIb) SE-dipping post-rift listric faults in the Cretaceous and Jurassic units merge into a basal detachment along the top of allochthonous extended canopy in the northeastern and central segments. (IV) SE-dipping post-rift normal faults offset the Cretaceous and Tertiary clastic units in the central and northeastern segments of the margin. (V) NE-SW-striking post-rift conjugate planar normal faults are associated with the deformation of Tertiary deposits above isolated salt diapirs in the southwestern segment of the margin.<br>
The extension amount varies along the margin, gradually increasing from 1.55% in the SW (volcanic) to 3.72% in the NE (non-volcanic). A higher extension of the northeastern segment of the margin in the NW-SE direction results in a higher (~19km) thickness of Mesozoic-Cenozoic sedimentary cover along this segment, while it is 10-12 km in the southwest. Syn-rift faults in the basement accommodate a greater amount of extension (1.17%-2.70%) than the faults formed during the post-rift phases of deformation (0.25%-1.02%) along the margin. The syn-rift listric normal faults in the oceanic domain contributed the most to the extension (56%-86%) compared to the syn-rift planar faults in the continental domain (14%-44%). In the northeastern segment of the margin, both the basement and sedimentary succession exhibit a higher fault intensity with a stretching factor of 1.1-2.2 compared to the southwestern segment, where the lower crustal stretching factor is lower: 1.1-1.4.<br><br>
The maximum syn-rift subsidence of 1035m - 1200m is reconstructed in the northeastern and central segments of the margin, respectively, at the end of the rifting stage, followed by slow post-rift thermal subsidence. The subsidence rate (m/Ma) for the top of the basement increases basinward along four cross-sections from 1.63 to 13.0. The oceanic domain of the northeastern and central segments of the margin exhibits a maximum subsidence gradient rate (12.15-13) due to crustal thinning with higher stretching factors resulting in greater sediment thickness. In contrast, the southwestern segment of the margin is characterized by the syn-rift subsidence of 775m (J200) with lower maximum subsidence rate (10.11) due to lower crustal thinning and sediment thickness.<br>
The estimated amount of isostatic rebound and decompaction vary along the cross-sections. The highest isostatic rebound of 2610 m is reconstructed for Middle Jurassic (J163) strata in the northeastern shelf and slope of the margin, where the maximum thickness of the unit (6.5km) is observed. Towards the southwest, no visible correlation is observed between high isostatic responses and sediment load in Jurassic units. Instead, the East Coast Magnetic Anomaly associated with the magmatic underplating zone and/or the volcanic layer in the transition zone between continental and oceanic crusts determines the localization of maximum isostatic rebound in the Jurassic units (1055m). For the younger units, sediment load and mini-basin localization accommodated by salt remobilization are the driving mechanisms for higher isostatic responses, similar to the northeastern part of the margin.</p>