Multiple reactivation and strain localization along a Proterozoic orogen-scale deformation zone: The Kongsberg-Telemark boundary in southern Norway revisited

Reactivation of intrabasement structures during rifting - A case study from offshore southern Norway

“…Previous studies have also correlated similar structures observed in seismic reflection data, showing the characteristic trough-peak-trough wavetrain, to mylonite zones as observed onshore (Fountain et al, 1984;Hurich et al, 1985;Reeve et al, 2013), with some offering direct control through outcrop and well data (Wang et al, 1989;Hedin et al, 2012;Lorenz et al, 2015). In addition, our observed thicknesses of c. 100 m are of a similar scale to those proposed in previous modelling studies (Fountain et al, 1984;Reeve et al, 2013), and the internal structure of these intra-shear zone mylonites display a similar anastomosing geometry to those observed elsewhere; for example, onshore Norway (Boundy et al, 1992;Scheiber et al, 2015), the central alps (Choukroune and Gapais, 1983), the Cap de Creus shear zone network (Druguet et al, 1997;Carreras, 2001;Carreras et al, 2010;Ponce et al, 2013) and southern Africa (Goscombe et al, 2003;Goscombe and Gray, 2008;Rennie et al, 2013). However, we must also consider that the observed 100 m scale mylonites only reflect one scale of localisation present within shear zones (Carreras, 2001); the top and base of thicker mylonite zones may not constructively interfere and produce a prominent seismic reflection, whereas thinner mylonite zones may not be resolved in our seismic data.…”

“…The mylonitic foliation, along with the overall layering, mean the shear zone is strongly mechanically anisotropic, with the mylonite zones being weaker than the surrounding relatively undeformed rocks (White et al, 1980;Chattopadhyay and Chakra, 2013). This strong heterogeneity may be preferentially exploited during later brittle reactivation of the shear zones (Gontijo-Pascutti et al, 2010;Salomon et al, 2015;Scheiber et al, 2015). In addition, varying thicknesses of mylonite zones and the degree of strain experienced may have different strengths, providing multiple potential sites for later faults to exploit during brittle reactivation of the shear zones.…”

“…Such pre-existing heterogeneities may; i) reactivate during later tectonic events; ii) act as nucleation sites for later rift-related faults; and iii) localise and modify the regional stress field, thus fundamentally modifying the physiography and evolution of overlying rifts. Field, seismic and potential field data indicate that the reactivation of intrabasement structures may influence the development of rift systems (Daly et al, 1989;Fraser and Gawthorpe, 1990;Maurin and Guiraud, 1993;Ring, 1994;Faerseth, 1996;Clemson et al, 1997;Morley et al, 2004;Paton and Underhill, 2004;Gontijo-Pascutti et al, 2010;Bellahsen et al, 2013;Bird et al, 2014;Whipp et al, 2014;Salomon et al, 2015;Scheiber et al, 2015), an observation further supported by numerical and analogue modelling (Huyghe and Mugnier, 1992;Faccenna et al, 1995;Bellahsen and Daniel, 2005;Henza et al, 2011;Autin et al, 2013;Chattopadhyay and Chakra, 2013;Tong et al, 2014). However, many of these relationships between intrabasement structure and rift systems are simply based on plan-view correlations, with little consideration given to their three-dimensional geometric relationships or kinematic interactions, primarily due to difficulties in imaging and constraining the 3D geometry of the intrabasement structure.…”

Complex Bedrock Fracture Patterns: A Multipronged Approach to Resolve Their Evolution in Space and Time

“…This saturation prevents the formation of new faults and instead triggers the structural reactivation of those preexisting fault sets that are suitably oriented with respect to a given stress field orientation (e.g., Holdsworth et al, ). Thus, the degree of saturation becomes an intrinsic property of the deforming system, and faults and fractures inherited from earlier deformation episodes steer the subsequent geometric, kinematic, and mechanic evolution (e.g., Rutter et al, ; Scheiber, Viola, et al, ).…”

A new tectonic model for the Palaeoproterozoic Kautokeino Greenstone Belt, northern Norway, based on high-resolution airborne magnetic data and field structural analysis and implications for mineral potential

“…In any case, the validity of tectonic models for orogens of any age should always be vigorously tested with structural and kinematic analysis of field data (e.g., Ramsay, 1980;Hanmer, 1986;Simpson & De Paor, 1993;Tavarnelli, 1997;Holdsworth et al, 2002;Jones et al, 2004;Viola et al, 2008a;Bergh et al, 2010;Scheiber et al, 2015). This is because ductile shear zones at all scales are an essential part of any orogenic belt, often accommodating strain during polyphase deformation histories (e.g., Sanderson & Marchini, 1984;Jones & Tanner, 1995;Tavarnelli et al, 2004).…”