4D analogue modelling of transtensional pull-apart basins

• Published in: Marine and petroleum geology 2009-09, Vol.26 (8), p.1608-1623
• Main Authors: Wu, Jonathan E., McClay, Ken, Whitehouse, Paul, Dooley, Tim
• Format: Article
• Language: English
• Subjects: Analogue modelling; Angles (geometry); Basins; Collapse; Dead Sea; Displacement; Earth sciences; Earth, ocean, space; En-echelon faults; Evolution; Exact sciences and technology; Faults; Hydrocarbons; Marine; Marine geology; Partitioning; Pull-apart basins; Pure strike-slip; Reconstruction; Sedimentary rocks; Strain partitioning; Three dimensional; Transtension; Vienna Basin
• ISSN: 0264-8172; 1873-4073
• DOI: 10.1016/j.marpetgeo.2008.06.007

Scaled sandbox models were used to investigate the 4D evolution of pull-apart basins formed above underlapping releasing stepovers in both pure strike-slip and transtensional basement fault systems. Serial sectioning and 3D volume reconstruction permitted analysis of the full 3D fault geometries. Results show that very different pull-apart basins are developed in transtension compared to pure strike-slip. Both types of models produced elongate, sigmoidal to rhomboidal pull-apart systems, but the transtensional pull-apart basins were significantly wider and uniquely developed a basin margin of en-echelon oblique-extensional faults. Dual, opposing depocentres formed in the transtensional model whereas a single, central depocentre formed in pure strike-slip. In transtension, a distinct narrow graben system formed above the principal displacement zones (PDZs). Cross-basin fault systems that linked the offset PDZs formed earlier in the transtensional models. Sequential model runs to higher PDZ displacements allowed the progressive evolution of the fault systems to be evaluated. In cross-section, transtensional pull-aparts initiated as asymmetric grabens bounded by planar oblique-extensional faults. With increasing displacement on the PDZs, basin subsidence caused these faults to become concave-upwards and lower in dip angle due to fault block collapse towards the interior of the basin. In addition, strain partitioning caused fault slip to become either predominantly extensional or strike-slip. The models compare closely with the geometries of natural pull-apart basins including the southern Dead Sea fault system and the Vienna Basin, Austria.