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

Calvín-Ballester, Pablo ; Casas-Sainz, Antonio (Universidad de Zaragoza)

Resumen: The Herrera Unit is located in the central sector of the Aragonese Branch of the Iberian Range (Zaragoza-Teruel). This unit constitutes the NE limb of a kilometric scale Variscan major anticline, with a predominant NW-SE to NNW-SSE trend and NE vergence. In its SW limb the Badules Unit crops out. The Datos thrust, a first order structure, superimposes the Badules unit onto the Herrera unit. Cambrian to Ordovician materials compose its hanging-wall, whereas Upper Cambrian to Devonian materials appear in its foot-wall. In this footwall a 4000 m thick series, essentially detrital, with Silurian and Devonian carbonate levels can be seen. South of the studied zone, the Lower Cambrian (Badules Unit) thrust over the Devonian (Herrera Unit). The Herrera Unit is characterized by thin-skinned tectonics involving two detachment levels: the lower one is constituted by Precambrian shales, and the upper one by Upper Silurian shales. The Silurian level, more than 1000 m thick, separates two structural levels with different deformation styles. In the Cambrian to Silurian materials that form the lowermost structural level, a duplex system characterizes the general structure, related to both detachment levels, with intermediate minor detachments. The East dipping thrusts could probably be the result of folded and tilted thrusts with eastward vergence, according to the general Variscan trend. This folding could be associated either with the late stages of the Datos thrust or represent the front of an antiformal stack. This structural configuration could also be explained by a backthrust system. A well developed cleavage (S1) affects the whole Cambrian to Silurian series and a second cleavage (S2) locally appears. The main system is an axial plane cleavage related to NNW-SSE folds, with a dominant East vergence and SSE plunge. Slaty cleavage appears in pelitic levels and fracture cleavage in sandstones. Depending on the spatial relation with the thrust, the upper detachment level shows different deformation styles attending to cleavage type and fold geometry. In general, NNW-SSE crenulation cleavage appears due to a previous sedimentary planar anisotropy. The Devonian, upper structural level is characterized by E.verging, NNW-SSE thrust and fault-related folds with axial plane cleavage.

Idioma: Inglés

DOI: 10.1144/SP394.3

Año: 2013

Publicado en: Special publication of the Geological Society of London 394, 1 (2013), 39-52
ISSN: 0305-8719

Tipo y forma: Artículo (PostPrint)

Área (Departamento): Área Geodinámica Interna (Dpto. Ciencias de la Tierra)