Rifting and pre‐rift lithosphere variability in the Orphan Basin, Newfoundland margin, Eastern Canada

Abstract

The Orphan Basin, lying along the Newfoundland rifted continental margin, formed in Mesozoic time during the opening of the North Atlantic Ocean and the breakup of Iberia/Eurasia from North America. To investigate the evolution of the Orphan Basin and the factors that governed its formation, we (i) analysed the stratigraphic and crustal architecture documented by seismic data (courtesy of TGS), (ii) quantified the tectonic and thermal subsidence along a constructed geological transect, and (iii) used forward numerical modelling to understand the state of the pre-rift lithosphere and the distribution of deformation during rifting. Our study shows that the pre-rift lithosphere was 200-km thick and rheologically strong (150-km-thick elastic plate) prior to rifting. It also indicates that extension in the Orphan Basin occurred in three distinct phases during the Jurassic, the Early Cretaceous and the Late Cretaceous. Each rifting phase is characterized by a specific crustal and subcrustal thinning configuration. Crustal deformation initiated in the eastern part of the basin during the Jurassic and migrated to the west during the Cretaceous. It was coupled with a subcrustal thinning which was reduced underneath the eastern domain and very intense in the western domains of the basin. The spatial and temporal distribution of thinning and the evolution of the lithosphere rheology through time controlled the tectonic, stratigraphic and crustal architecture that we observe today in the Orphan Basin. EAGE sedimentary basins. Using 2D seismic data (courtesy of TGS), tectonic subsidence analysis and 2D numerical modelling, we attempt to (i) determine and quantify the syn-and post-rift subsidence in the Orphan Basin, (ii) describe the spatial and temporal distribution of the various rifting phases and the related crustal and subcrustal amounts of thinning, and (iii) investigate the thickness and strength of the lithosphere prior to, and during, rifting.

Regional stratigraphy and subsidence of Orphan Basin near the time of breakup and implications for rifting processes

“…Very thick initial values for the crustal (50 km) and mantle lithospheric (200 km) thicknesses, such as those proposed by Gouiza et al . () provide even less uplift than the models shown. Such high initial values are not supported by observations on relatively unstretched proximal regions of the Newfoundland margin (Hall et al ., ) or on nearby Flemish Cap (Funck et al ., ).…”

“…While the models can only roughly approximate the actual processes responsible for the observed tectonostratigraphy, it is difficult to avoid the requirement for significant mantle thinning in the AU to SU time interval. Some studies have suggested an additional stretching phase with crustal involvement in Late Cretaceous time (Enachescu et al ., ; Gouiza et al ., ). However, this makes it more difficult to fit the observations, as dense mantle replaces lighter crust resulting in even greater subsidence.…”

“…Recently, Gouiza et al . () described the results of quantitative modelling of the stratigraphy across Orphan Basin including the flexural response of the lithosphere to stretching and sediment loading. Their results, while different from ours in some respects, also highlight the need for depth‐dependent extension with more mantle than crustal thinning.…”

Conjugate margins — An oversimplification of the complex southern North Atlantic rift and spreading system?

“…The structure and evolution of many of the passive margins of the southern North Atlantic are known in detail from decades of work (Shannon et al, 1995;Hitchen, 2004;Naylor and Shannon, 2005;Tucholke et al, 2007;Sibuet et al, 2007a;Welford et al, 2012;Magee et al, 2014;Gouiza et al, 2015Gouiza et al, , 2016Dafoe et al, 2017;Roberts et al, 2018;Sandoval et al, 2019). As a result, some of the best-studied passive margins are located in this region, such as the Grand Banks, offshore Newfoundland, and the Iberian margin (Eddy et al, 2017)…”

“…Despite the research focus on the margins of the southern North Atlantic, the mechanisms driving extensional deformation in the continental domains leading to the creation of new oceanic crust, and thus passive margins, remains a topic of considerable current research interest (Nirrengarten et al, 2018;Gouiza and Paton, 2019). Current areas of research in this area include, but are not limited to: 1) timing of spatially and temporally overlapping and interacting rifting events (Gouiza et al, 2015), 2) sediment distribution, provenance and facies (Tyrrell et al, 2007), 3) timing of structural development and its relationship with hydrocarbon prospectivity (Enachescu et al, 2004), 4) the role of pre-existing structures in controlling rift evolution and margin architecture (Doré et al, 1999), and 5) the causes and consequences of rift-and breakup-related magmatism (Keen et al, 2014;Peace et al, 2018c).…”