The Role of Premagmatic Rifting in Shaping a Volcanic Continental Margin: An Example From the Eastern North American Margin

Abstract

Both magmatic and tectonic processes contribute to the formation of volcanic continental margins. Such margins are thought to undergo extension across a narrow zone of lithospheric thinning (~100 km). New observations based on existing and reprocessed data from the Eastern North American Margin contradict this hypothesis. With~64,000 km of 2-D seismic data tied to 40 wells combined with published refraction, deep reflection, receiver function, and onshore drilling efforts, we quantified along-strike variations in the distribution of rift structures, magmatism, crustal thickness, and early post-rift sedimentation under the shelf of Baltimore Canyon Trough (BCT), Long Island Platform, and Georges Bank Basin (GBB). Results indicate that BCT is narrow (80-120 km) with a sharp basement hinge and few rift basins. The seaward dipping reflectors (SDR) there extend~50 km seaward of the hinge line. In contrast, the GBB is wide (~200 km), has many syn-rift structures, and the SDR there extend~200 km seaward of the hinge line. Early post-rift depocenters at the GBB coincide with thinner crust suggesting "uniform" thinning of the entire lithosphere. Models for the formation of volcanic margins do not explain the wide structure of the GBB. We argue that crustal thinning of the BCT was closely associated with late syn-rift magmatism, whereas the broad thinning of the GBB segment predated magmatism. Correlation of these variations to crustal terranes of different compositions suggests that the inherited rheology determined the premagmatic response of the lithosphere to extension.

Modification of Crust and Mantle Lithosphere Beneath the Southern Part of the Eastern North American Passive Margin

“…We proposed that the difference in the lateral width of the transitional crust along the ENAM indicates that the crust experienced more localized extension in the south than in the north during the Mesozoic rifting. Recent studies (e.g., Greene et al, 2020;Lang et al, 2020) suggest that the crust in the southern ENAM had a stronger rheology than in more northern regions, which limited the crustal extension during rifting, supporting our hypothesis. In correspondence, the estimated volume of rifting-related magmatism is less in the southern ENAM than in the north (Greene et al, 2020).…”

“…Our model in the southern ENAM reveals that the Moho deepens from ∼15 km to ∼40–45 km over a horizontal distance of ∼70 km across the oceanic‐continental margin (Figures 3 and ). In comparison, the Moho depth increases gradually from ∼15 km landward to ∼45–50 km over a wide zone of ∼200 km beneath the continental shelf of southern New England (e.g., Lang et al., 2020; Pope et al., 2016). We proposed that the difference in the lateral width of the transitional crust along the ENAM indicates that the crust experienced more localized extension in the south than in the north during the Mesozoic rifting.…”

The influence of crustal strength on rift geometry and development – Insights from 3D numerical modelling

“…Larsen et al, 2008;Tiberi et al, 2019), previous studies have demonstrated that, across multiple scales, strain preferentially localises into relatively weaker areas with stronger bodies proving resistant to extension (e.g. Beniest et al, 2017;Lang et al, 2020;Wright et al, 2020;Samsu et al, 2021). However, less is known about how the characteristic geometry and development of fault networks and rift systems varies across these relatively 'strong' and 'weak' areas during extension.…”

Magmatism at Passive Margins: Effects of Depth‐Dependent Wide Rifting and Lithospheric Counterflow

“…It is also worth to note that the effect of increased magmatism with margin width does not exclude feedbacks from magmatism, which are not included in this study. For example, melt intrusion may weaken the lithosphere and ultimately limit the width of margins (Bastow et al., 2010; Buck, 2006; Keir et al., 2006; Lang et al., 2020). Such weakening may be particularly efficient at high mantle temperature when the melt production rate is high.…”