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

Abstract

Large-scale faults in the continental crust are significant features that control the evolution of sedimentary basins and intraplate mountain chains. Deciphering their evolution is a significant task because faults slip and reactivate in a variety of geological settings. In this work, clay gouges of two major orogen-scale, long-lived faults in northern Iberia, the Río Grío and Vallès-Penedès Faults, were investigated by X-ray diffraction and K-Ar isotopic analysis. Illite polytype determinations of 44 subfractions (from <0.1 to 10 μm) allowed us to discriminate between authigenic/synkinematic illite crystals formed during faulting and detrital illite crystals inherited from the host rock. K-Ar dating provided a detailed set of ages corresponding to key stages of the thermotectonic evolution of the Iberian Plate: (a) the Permian to Late Triassic extensional/transtensional activity associated to the emplacement of Late Variscan magmatic bodies and hydrothermal mineralizations, (b) the opening of the Central Atlantic Rift during Late Triassic-Early Jurassic times, (c) the Late Jurassic-Early Cretaceous rifting that led to the development of Mesozoic extensional/transtensional basins in northern Iberia, (d) the final stage of the anticlockwise rotation of the Iberian Plate with respect to Eurasia and the accommodation of the first Pyrenean compressional pulses in Campanian time, and (e) the positive inversion of Mesozoic extensional basins due to far-field stresses associated with the Alpine orogeny during the Paleogene. The results highlight that thermotectonic conditions characterized by high-geothermal gradients strongly favor fault movement and neoformation of clay minerals in fault gouges, regardless of the prevailing tectonic regime.

A reconstruction of Iberia accounting for Western Tethys–North Atlantic kinematics since the late-Permian–Triassic

“…Several studies have suggested that a left-lateral shear zone can be recognized along the Iberian Range and the Basque-Cantabrian rifts system. Geological evidence includes the High Tagus Fault in the Iberian Range (Aldega et al, 2019;Aurell et al, 2019) and the Ventaniella Fault in the Basque-Cantabrian region (e.g., Tavani et al, 2011). The latter fault is often considered in recent reconstructions to accommodate the Iberia-Ebro movement alone (Tugend et al, 2015;Nirrengarten et al, 2018).…”

“…It suggests that the transcurrent deformation that results from the eastwards movement of Iberia occurred mainly during the Late Jurassic-Early Cretaceous in northern Iberia along a 100 km scale pull-part or en échelon rift basins formed by the NW-SE-trending Iberian massifs. Indeed, along these massifs, several extensional basins recorded major subsidence and strike-slip deformation during the late-Permian to middle-Cretaceous time interval (Alvaro et al, 1979;Salas et al, 2001;Aldega et al, 2019;Aurell et al, 2019;Soto et al, 2019). However, no geological evidence for lithosphere-scale strike-slip movements has yet been clearly defined in the intra-Iberian basins.…”

Tectono‐sedimentary evolution of Jurassic–Cretaceous diapiric structures: Miravete anticline, Maestrat Basin, Spain

“…This succession, was inferred to range from earliest Palaeocene to Miocene in age and was grouped into six tectono‐sedimentary units bounded by unconformities associated with successive Alpine compressional events (González & Guimerà, 1993; Simón, 2004). Recently, K‐Ar isotopic dating of illites from clay gouges near the SE front of the Iberian Ranges (Río Grío Fault) provided three groups of absolute ages, for the first time in the study area (Aldega et al, 2019). The Río Grío Fault system was active during Permian‐Triassic and Late Jurassic (Mesozoic rifting phases) and then recorded the compression stages during Campanian (72 Ma) and middle Eocene (43 Ma).…”

Late Miocene-Early Pliocene Out-of-Sequence Thrusting in the Southern Apennines (Italy)

“…Recently, many studies have provided temporal constraints to the fault activity in several fold-and-thrust belts worldwide through different geochronological methods. They include isotopic K-Ar and Ar-Ar dating for cataclasites containing silicate minerals (e.g., [11][12][13]) and U-Th/He, U-Pb dating for the synkinematic carbonate tectonites (e.g., [14,15]). Different authors have applied these methodological approaches also to the study of thrusts in the Apennines (e.g., [16]), and in some cases being able to date multiple reactivations of the thrust faults especially in the case of positive inversion that makes difficult the interpretation of the previous fault kinematics and deformation history (e.g., [17]).…”