Determining the three-dimensional geometry of a dike swarm and its impact on later rift geometry using seismic reflection data

Abstract

Dike swarm emplacement accommodates extension during rifting and large igneous province (LIP) formation, whereas ancient dike swarms can localize strain during later tectonic events. Deciphering three-dimensional (3-D) dike swarm geometry is critical to accurately calculating magma volumes and magma-assisted crustal extension, allowing syn-emplacement mantle and tectonic processes to be interrogated, and for quantifying the influence ancient dike swarms have, post-emplacement, on faulting. However, the 2-D nature of Earth's surface, combined with the difficulties in imaging sub-vertical dikes on seismic reflection data, and the relatively low resolution of geophysical data in areas of active diking, means that our understanding of dike swarm geometry at depth is limited. We examine an ~25-km-wide, >100-km-long, westsouthwest-trending dike swarm imaged, due to post-emplacement rotation to shallower dips, in high-quality 2-D and 3-D seismic reflection data offshore southern Norway. Tuned reflection packages correspond to thin (<75 m thick), closely-spaced dikes. These data provide a unique opportunity to image and map an ancient dike swarm at variable

Terrane Boundary Reactivation, Barriers to Lateral Fault Propagation and Reactivated Fabrics: Rifting Across the Median Batholith Zone, Great South Basin, New Zealand

“…Prominent fabrics on seismic reflection data may be related to a number of different features including sedimentary strata, fault plane reflections, highly foliated basement rocks and shear zones (e.g., Fazlikhani et al, 2017;Lenhart et al, 2019;Phillips et al, 2016), and dyke swarms (e.g., Abdelmalak et al, 2015;Phillips et al, 2017). The E-W fabric appears related to the Terrane Boundary Fault and shear zone, appearing to link with the structure to the south (Figure 11).…”

“…Preexisting structures in the crust may also localize deformation and control the geometry and evolution of fault and rift systems (e.g., Daly et al, 1989;Dawson et al, 2018;Fazlikhani et al, 2017;Fossen et al, 2016;Morley, 2017;Mortimer et al, 2016;Peace et al, 2017;Phillips et al, 2016;Rotevatn, Kristensen, et al, 2018;Vasconcelos et al, 2019). In addition, preexisting structures and fabrics at outcrop scale may be exploited by and control the geometry of later faults and fractures (Chattopadhyay & Chakra, 2013;De Paola et al, 2005;Dichiarante et al, 2016;Duffy et al, 2015;Kirkpatrick et al, 2013;Morley, 2010;Morley et al, 2004;Mortimer et al, 2016;Paton & Underhill, 2004;Phillips et al, 2017). Equally, preexisting structures do not always influence rift physiography; some may remain passive during subsequent tectonic events, while certain structures may only be selectively reactivated (e.g., Reeve et al, 2013;Roberts & Holdsworth, 1999).…”

Pre-inversion normal fault geometry controls inversion style and magnitude, Farsund Basin, offshore southern Norway

“…Transtensional reactivation of the STZ during the Carboniferous-Permian was associated with rift activity and voluminous magmatism, including the emplacement of the WSW-trending Farsund Dyke Swarm (Fig. 2b) 105 Heeremans et al, 2004;;Wilson et al, 2004;Phillips et al, 2017;Malehmir et al, 2018). However, no Carboniferous-Permian fault activity is identified in the Farsund Basin (Phillips et al, 2018), although some pre-upper Permian faulting, likely related to Carboniferous-Permian extension, occurred in the Norwegian-Danish and Egersund basins (Skjerven et al, 1983;Jackson and Lewis, 2013) (Fig.…”

Deeply buried ancient volcanoes control hydrocarbon migration in the South China Sea

“…32-16.5 Ma). Dykes commonly intrude the crust during the continent rifting (e.g., Kendall, Stuart, Ebinger, Bastow, & Keir, 2005;Maccaferri et al, 2014), but such structures are not typically imaged in seismic reflection data because their (sub-) vertical attitude does not reflect acoustic energy back to the surface (e.g., Phillips, Magee, Jackson, & Bell, 2018). Such fault-controlled magma ascent is consistent with the spatial and genetically relationships between volcanoes and faults in active and ancient sedimentary basins (e.g., Gaffney, Damjanac, & Valentine, 2007;Isola, Mazzarini, Bonini, & Corti, 2014;Mazzarini, 2007;Magee, Jackson, & Schofield, 2013;Magee, Duffy et al, 2016;Weinstein et al, 2017), and in numerical models (e.g., Le Corvec, Spörli, Rowland, & Lindsay, 2013;Maccaferri, Rivalta, Keir, & Acocella, 2014).…”

“…We highlight that sub-vertical dykes, not hosted by faults, may have also fed the volcanoes. Dykes commonly intrude the crust during the continent rifting (e.g., Kendall, Stuart, Ebinger, Bastow, & Keir, 2005;Maccaferri et al, 2014), but such structures are not typically imaged in seismic reflection data because their (sub-) vertical attitude does not reflect acoustic energy back to the surface (e.g., Phillips, Magee, Jackson, & Bell, 2018). Furthermore, even if present, dykes would likely be located in the very poorly imaged zone directly beneath the volcanoes, compromising their imaging and recognition (Figures 4a,b and 7).…”