Tectonothermal evolution of a foreland fold and thrust belt: the Cantabrian Zone (Iberian Variscan belt, NW Spain)

Abstract

Analysis of the conodont colour alteration index and the Kübler index of illite allowed us the characterization of four types of very low‐ or low‐grade metamorphism in the Cantabrian Zone (CZ) and determination of their regional and temporal distribution. These types are: (1) an orogenic Variscan metamorphism present only in restricted areas of the western and north‐western parts of the CZ where epizonal conditions are reached; (2) a burial metamorphism that appears in the basal part of some nappes, where anchizonal conditions are sometimes achieved; the thermal peak preceded emplacement of the nappes; (3) a late‐Variscan metamorphism in the southern and south‐eastern parts of the CZ; a cleavage, cutting most of the Variscan folds, is associated with this metamorphism, which has been related to an extensional episode; (4) a contact metamorphism and hydrothermal activity associated with minor intrusive bodies. The extension continued after the Variscan deformation giving rise to hydrothermal activity during Permian times.

Thermal history of the Sabero Coalfield (Southern Cantabrian Zone, NW Spain) as revealed by apatite fission track analyses from tonstein horizons: implications for timing of coalification

“…The Permian heating phase in the Sabero Coalfield (Fig. 3) was probably caused by the well-known magmatism and its associated hydrothermal activity under an extensional tectonic regime (Aller et al 2005;García-López et al 1997, 2007. The important heating phase had a significant thermal effect due to a deep source of heat.…”

“…Therefore, new models (Fig. 3) were constructed taking into account previous thermal history studies in the SCZ (García-López et al 1997, 2007Ayllon 2003;Ayllon et al 2003;Frings et al 2004;Aller et al 2005;Frings and Warr 2012;Botor 2012), which indicated that the Late Carboniferous-Permian period was the main heating time. Vitrinite reflectance data were used to calculate the maximum palaeotemperatures (values T max 2 and T max 3 in Fig.…”

“…Geological data combined with thermal models of AFT data indicate that Stephanian strata reached the maximum palaeotemperatures in the Permian period, which was therefore the major time of the coalification processes. The Permian magmatic activity was responsible for a high heat flow, which, with the added effect of sedimentary burial, could account for 1 3 stages of the Variscan orogeny at the end of the Carboniferous to the early Permian resulted in basin closure and inversion (Julivert 1971;Alonso et al 1995;García-López et al 1997, 2007Bastida et al 1999). This study examines the thermal history of one of these small basins (~12-15 km long and 3-4 km wide) located along the eastern end of the Sabero-Gordon fault line (Fig.…”

“…These basins are considered to have initially formed as small pullapart basins along strike-slip fault systems under a Late Carboniferous syn-orogenic transtensional regime (Julivert 1971;Reading 1975;Heward and Reading 1980;Wagner and Winkler-Prins 1985;Alonso et al 1995;García-López et al 1997, 2007Bastida et al 1999). Many of these basins in the Southern Cantabrian Zone (SCZ) were structurally controlled by a major E-W trending Variscan strikeslip fault system, named the Sabero-Gordon Line (Julivert 1971;Reading 1975;Heward and Reading 1980;Alonso et al 1995;García-López et al 1997, 2007Bastida et al 1999). Transpressional faulting and folding during the later Abstract Apatite fission track (AFT) central ages from Carboniferous (Stephanian) tonsteins of the Sabero Coalfield, NW Spain, range from 140.8 ± 7.5 to 65.8 ± 8.1 Ma (Cretaceous), with mean c-axis projected track length values ranging from 12.5 to 13.4 μm.…”

Conodont alteration and tectonothermal evolution of a diagenetic unit in the Iberian Variscan belt (Ponga-Cuera unit, NW Spain)

“…In addition, an anchizonal or epizonal E-W band appears in the southern and southeastern parts of the Cantabrian zone. This band is associated with a nearly horizontal or moderately north-dipping cleavage that cuts across the main Variscan folds, and has been related to a late Variscan extensional episode that occurred near the Carboniferous-Permian boundary , 2007Bastida et al 2004). Hydrothermal activity related to normal faults continued during Permian and Mesozoic times.…”