Folded Variscan thrusts in the Herrera Unit of the Iberian Range (NE Spain)

Abstract

The Variscan structure of the Herrera unit (Iberian Chain, NE Spain) is characterized by a system of NNW–SSE-striking, east-verging, foreland-dipping thrusts, generated in a thin-skinned context, whose formation was favoured by the presence of two main detachment levels (Precambrian and Silurian shales). During the formation of the thrust system (first phase of deformation, D1), the thrust sheets were deformed internally, mainly by asymmetrical folds with axial surface cleavage and east-verging thrusts; the normal evolution of the thrust system and the emplacement of an underlying thrust sheet resulted in progressive tilting and stacking, thus generating a foreland-dipping thrust system. These structures were folded and tilted by the emplacement of the Datos thrust (second phase of deformation, D2), generating an associated deformation characterized by subvertical folds with axial surface cleavage, with slight east vergence. These structures can obliterate the previous D1 structures in the sector near the Datos thrust. D1 and D2 structures have not been observed in the same outcrops, but the relationship between bedding and cleavage as well as cleavage relationship with other structures allows discrimination between the two cleavage sets. Based on the features of Palaeozoic rocks of the Iberian Range and the Iberian Massif, we support the idea that the Herrera unit belongs to the Cantabrian Zone.

Late Paleozoic Iberian orocline(s) and the missing shortening in the core of Pangea. Paleomagnetism from the Iberian Range.

“…1A; Pastor-Galán et al, 2012b) but it also crops out in areas of the Aragonese Branch of the Iberian Range in E Iberia ( Fig. 1B; Carls, 1983;Calvín-Ballester and Casas, 2014), where we performed our study (Figs. 1B and 2).…”

“…Gozalo and Liñán, 1988) 1B and 2). The Herrera unit is characterized by an imbricate thrust system with a foreland-dipping geometry in which the deformation and cleavage diminishes eastwards (Calvín et al, 2014).…”

“…Calvín et al, 2014 and references therein). A series of 1500 m-thick Mesozoic rocks (Calvín et al, 2014) overlies the Paleozoic units. Both sequences underwent gentle folding during the Alpine compression event with no associated penetrative structures (Cortés-Gracia and Casas-Sainz, 1996).…”

Late Paleozoic Iberian Orocline(s) and the Missing Shortening in the Core of Pangea. Paleomagnetism From the Iberian Range

“…Illite crystallinity and conodont color alteration indexes are consistent with diagenetic conditions to very low grade metamorphism (e.g., García‐López et al, ; Pastor‐Galán et al, ). The Cantabrian Zone is mostly preserved in NW Iberia in the core of the Cantabrian Orocline (Figure 1a; Pastor‐Galan, Gutierrez‐Alonso, Zulauf, et al, ), but it also crops out in areas of the Aragonese Branch of the Iberian Range in East Iberia (Figure 1b; Calvín‐Ballester & Casas‐Sainz, ; Carls, , ), where we performed our study (Figures 1b and ).…”

“…Whereas the Herrera unit is the continuation of the foreland (Cantabrian Zone), the Badules unit represents more internal zones of the orogen (e.g., Gozalo & Liñan, ). The Herrera Unit preserves over 9,000‐m‐thick sedimentary sequence containing a Cambrian–Silurian alternation of sandstones and shales and, over it, the studied Upper Silurian–Devonian series of shales, sandstones, and limestones (Luesma, Nogueras, and Mariposas Formations; Figure ; Calvín‐Ballester & Casas‐Sainz, ; Pérez‐Pueyo et al, , and references therein) that crop out at the south of the unit (Figures 1b and ). The Herrera unit is characterized by an imbricate thrust system with a foreland‐dipping geometry in which the deformation and cleavage diminishes eastward (Calvin et al, ).…”