Continental break-up mechanism; lessons from intermediate- and fast-extension settings

Abstract

Continental break-up mechanisms vary systematically between slow- and fast-extension systems. Slow-extension break-up has been established from studies of the Central Atlantic, European and Adria margins. This study focuses on the intermediate and fast cases from Gabon and East India, and draws from the interpretation of reflection seismic, gravimetric and magnetic data.Interpretation indicates continental break-up via continental mantle unroofing in all systems, with modifications produced by magmatism in faster-extension systems. Break-up of the intermediate-extension Gabon system involves partial upper continental crustal decoupling from continental mantle; whereas, in the fast East Coast India system, decoupled and lower-crustal regimes underwent upwarping in ‘soggy’ zones in the footwalls of major normal faults. Usually, upper-crustal break-up is affected by pre-existing anisotropies, which form systems of constraining ‘rails’ for extending continental crust. This modifies the local stress regimes. They regain a regional character as the function of constraining rails vanishes during progressive unroofing of the upper mantle. Different regions attain different amounts of upper-crustal stretching prior to the break-up. The break-up location is then controlled by the upper-crustal energy balance principle of ‘wound linkage’, by which the minimum physical work is performed for linking upper-crustal ‘wounds’, leading to successful upper-crustal break-up.Supplementary material:Supplementary information and figures on the modelling of the mechanisms and architecture is available at http://www.geolsoc.org.uk/SUP18525.

Crustal Architecture and Nature of Continental Breakup Along a Transform Margin: New Insights From Tanzania‐Mozambique Margin

“…The previous phase of unsuccessful Karoo rifting already weakened the lithospheric strength and thermal state due to voluminous magmatism, which possibly accelerated the second rifting phase to successful rifting. The faster rifting phase is characterized by increased volcanism, oblique, and localized accommodation zones (Nemčok, Stuart, et al, ). Interestingly, in this case a faster rifting process finally ends up to an ultraslow spreading.…”

Transform margins: development, controls and petroleum systems – an introduction

“…The breakup trajectory in the brittle upper crust usually follows the Andersonian geometry of the normal and strike-slip faults with respect to the stress field that resulted in the breakup, unless their geometry is affected by pre-existing anisotropy. Examples of zig-zag trajectories with normal, oblique-slip or strike-slip faulting-dominated control come from the offshore Gabon (Nemčok et al 2012a), offshore East India (Nemčok et al 2012c) and both sides of the Equatorial Atlantic (Nemčok et al 2012b). Subsequently, the initial spreading centres have to clear their contact with the continental -oceanic transform changing into transform margin segments.…”

“…Interpretation of seismic imagery tied to wells in the successful Krishna -Godavari and Cauvery rift zones linked via the Coromandal transform indicates that they can develop coevally to postdating the development of the rift zone-controlling faults ( Fig. 5b in Nemčok et al 2012a). The former example documents a development of accommodation zones in the study area as starting with the reactivation of the pre-existing zones of weakness prior or coeval with the propagation of the riftbounding faults and finishing with the arrest of the border faults and transfer of displacement (Younes & McClay 2002).…”

Continental Interior and Edge Breakup at Convergent Margins Induced by Subduction Direction Reversal: A Numerical Modeling Study Applied to the South China Sea Margin

“…Tectonics situations, tectonic loading, rollback process, preexisting weak structure, extension rate, crustal rheology, subduction depth, and thermal structure can control the first-order patterns of continental breakup (e.g., Burov & Watts, 2006;Dal Zilio et al, 2017;Duclaux et al, 2019;Gueydan & Précigout, 2014;Lavier & Manatschal, 2006;Nemčok et al, 2013;Pérez-Gussinyé et al, 2003;Ros et al, 2017;Svartman Dias et al, 2015;Tetreault & Buiter, 2018). Among these factors, slab rollback is the common dynamics of continental rifting at convergent margins (e.g., Leng & Gurnis, 2011;Sdrolias & Muller, 2006;Stern, 2002).…”

“…Some of their end‐members emphasized the role of plume‐lithospheric interaction (e.g., Behn et al, 2004; Cande & Stegman, 2011; Husson, 2012; Jolivet et al, 2018; Koptev et al, 2015, 2019; Mondy et al, 2018; Phillips & Bunge, 2005; Yamato et al, 2013; Yoshida & Hamano, 2015), while others related the continental rifting to the tensional stresses generated at the plate boundary (e.g., Choi et al, 2013; Huismans & Beaumont, 2003; Le Pourhiet et al, 2018; Liao et al, 2013; Marotta et al, 2009; Naliboff et al, 2017; Pérez‐Gussinyé et al, 2006). A series of numerical modeling studies further showed that, in both situations, tectonic loading, rollback process, preexisting weak structure, extension rate, crustal rheology, subduction depth, and thermal structure can control the first‐order patterns of continental breakup (e.g., Burov & Watts, 2006; Dal Zilio et al, 2017; Duclaux et al, 2019; Gueydan & Précigout, 2014; Lavier & Manatschal, 2006; Nemčok et al, 2013; Pérez‐Gussinyé et al, 2003; Ros et al, 2017; Svartman Dias et al, 2015; Tetreault & Buiter, 2018). Among these factors, slab rollback is the common dynamics of continental rifting at convergent margins (e.g., Heuret & Lallemand, 2005; Leng & Gurnis, 2011; Sdrolias & Muller, 2006; Stern, 2002).…”