Multidisciplinary approach to constrain kinematics of fault zones at shallow depths: a case study from the Cameros–Demanda thrust (North Spain)

Abstract

Thrusting at shallow depths often precludes analysis by means of structural indicators effective in other geological contexts (e.g., mylonites, sheath folds, shear bands). In this paper, a combination of techniques (including structural analysis, magnetic methods, as anisotropy of magnetic susceptibility and paleomagnetism, and paleothermometry) is used to define thrusting conditions, deformation, and transport directions in the Cameros–Demanda thrust (North Spain). Three outcrops were analyzed along this intraplate, large-scale major structure having 150 km of outcropping length, 30 km of maximum horizontal displacement, and 5 km of vertical throw. Results obtained by means of the different techniques are compared with data derived from cross sections and stratigraphic analysis. Mixed-layer illite–smectite and vitrinite reflectance indicating deep diagenetic conditions and mature stage of hydrocarbon generation suggests shallow depths during deformation, thus confirming that the protolith for most of the fault rocks is the footwall of the main thrust. Kinematic indicators (foliation, S/C structures, and slickenside striations) indicate altogether a dominant NNW movement of the hanging wall in the western zone and NE in the eastern zone of the thrust, thus implying strain partitioning between different branches of the main thrust. The study of AMS in fault rocks (nearly 400 samples of fault gouge, breccia, and microbreccia) indicates that the strike of magnetic foliation is oblique to the transport direction and that the magnetic lineation parallelizes the projection of the transport direction onto the kmax/kint plane in sites with strong shear deformation. Paleomagnetism applied to fault rocks indicates the existence of remagnetizations linked to thrusting, in spite of the shallow depth for deformation, and a strong deformation or scattering of the magnetic remanence vectors in the fault zone. The application of the described techniques and consistency of results indicate that the proposed multidisciplinary approach is useful when dealing with thrusts at shallow crustal levels

Strain indicators and magnetic fabric in intraplate fault zones: Case study of Daroca thrust, Iberian Chain, Spain

“…1B). Crustal-scale strike-slip faults, probably inherited from the Late-Variscan fracturing episodes Matte, 1975, 1977) can be recognized within the Aragonian Branch (De Vicente et al, 2011;Gutiérrez et al, 2012;Casas et al, 2017). They are roughly parallel to the Cenozoic structural trend (NW-SE) and cut across the Palaeogene and Neogene infill of intra-mountain sedimentary basins.…”

“…In addition, because of the structural complexity of fault zones in intraplate areas (and of their kinematic indicators) at shallow crustal levels, a combination of techniques is a convenient approach for deciphering their kinematics. In this sense, anisotropy of magnetic susceptibility (AMS) has demonstrated to be a reliable method for unravelling the kinematic evolution of faults (Solum and van der Pluijm, 2009;Levi et al, 2014;Moreno et al, 2014;Pomella, 2014;Braun et al, 2015;Keskinva et al, 2016;Casas et al, 2017) due to the possibility of averaging datasets even where structures are not well developed at the outcrop scale.…”

Unraveling Multiple Thermotectonic Events Accommodated by Crustal‐Scale Faults in Northern Iberia, Spain: Insights From K‐Ar Dating of Clay Gouges

“…The most prominent thrust systems of the chain reflect a thin‐skinned style, with the major thrusts detaching on low‐strength Upper Triassic shales and evaporites. Thrusts generally trend NW‐SE but become E‐W, at both the northwestern and southeastern terminations of the chain (Casas‐Sainz et al, ; Guimerà, ). They are N‐S in the Altomira Range.…”

Remagnetizations used to unravel large‐scale fold kinematics: A case study in the Cameros Basin (Northern Spain)

“…Within the Iberian Range, the geometry of previous structures, the changes in thickness of the Mesozoic sedimentary cover and the presence or absence of detachment levels yielded the coexistence of different tectonic styles [e.g., Álvaro , ; Guimerà and Alvaro , ; Liesa et al ., ]. These mixed behaviors have been reported even within the same geological setting, as occurs in the Cameros unit [e.g., Casas‐Sainz , ; Casas‐Sainz et al ., ].…”

“…Most samples were collected in sites showing NE dipping strata, except for the Oliván Group sites that are often deflected from this trend and show anomalous tilts associated with the Cameros thrust front [ Casas‐Sainz et al ., ]. This is probably related to an accommodation of strata over the footwall ramp during the Cenozoic inversion.…”