Abstract We present new fission-track and (U–Th)/He data from apatite and zircon in order to reconstruct the exhumation of the Sierra de Cameros, in the northwestern part of Iberian Range, Spain. Zircon fission-track ages from samples from the depocentre of the basin were reset during the metamorphic peak at approximately 100 Ma. Detrital apatites from the uppermost sediments retain fission-track age information that is older than the sediment deposition age, indicating that these rocks have not exceeded 110 °C. Apatites from deeper in the stratigraphic sequence of the central part of the basin have fission-track ages of around 40 Ma, significantly younger than the stratigraphic age, recording the time of cooling after peak metamorphic conditions. Apatite (U–Th)/He ages in samples from these sediments are 31–40 Ma and record the last period of cooling during Alpine compression. The modelled thermal history derived from the uppermost sediments indicates that the thermal pulse associated with peak metamorphism was rapid, and that the region has cooled continuously to the present. The estimated palaeogeothermal gradient is around 86 °C km −1 and supports a tectonic model with a thick sedimentary fill ( c . 8 km) and explains the origin of the low-grade metamorphism observed in the oldest sediments.

Abstract Anisotropy of magnetic susceptibility data are presented for samples from the anatectic complex of Toledo and the Mora batholith. The units located at the axial part of the Central Hercynian belt are separated by an important listric fault. Anatectic granites (Layos granite), epizonal granites (Mora granite) and, to a lesser extent, high-grade metamorphic rocks and metasediments are considered in this work in order to characterize their magnetic fabric and determine their structural significance in the framework of a large-scale extensional deformation of Late Variscan age. Samples from the Layos granites (footwall) show a magnetic lineation compatible with the stretching related to ductile shear deformation of the Toledo shear zone, which was responsible for the exhumation of the anatectic complex. During the exhumation, the folding of a previous metamorphic foliation in the anatectic complex took place, which is also recognized from the magnetic pattern of the minimum susceptibility axes of Layos granite. On the contrary, the magnetic fabric of the epizonal Mora granites (hanging wall), which intruded at the beginning of the extensional Late Variscan tectonics, mainly reflects magmatic processes.

The Layos Granite forms elongated massifs within the Toledo Complex of central Spain. It is late-tectonic with respect to the F2 regional phase and simultaneous with the metamorphic peak of the region, which reached a maximum temperature of 800–850°C and pressures of 400–600 MPa. Field studies indicate that this intrusion belongs to the “regional migmatite terrane granite” type. This granite is typically interlayered with sill-like veins and elongated bodies of cordierite/garnet-bearing leucogranites. Enclaves are widespread and comprise restitic types (quartz lumps, biotite, cordierite and sillimanite-rich enclaves) and refractory metamorphic country-rocks including orthogneisses, amphibolites, quartzites, conglomerates and calc-silicate rocks. These granites vary from quartz-rich tonalites to melamonzogranites and define a S-type trend on a QAP plot. Cordierite and biotite are the mafic phases of the rocks. The particularly high percentage of cordierite (10%–30%) varies inversely with the silica content. Sillimanite is a common accessory mineral, always included in cordierite, suggesting a restitic origin. The mineral chemistry of the Layos Granite is similar to that of the leucogranites and country-rock peraluminous granulites (kinzigites), indicating a close approach to equilibrium. The uniform composition of plagioclase (An 25 ), the high albitic content of the K-feldspar, the continuous variation in the Fe/Mg ratios of the mafic minerals, and the high Ti content of the biotites (2.5–6.5%) suggest a genetic relationship. Geochemically, the Layos Granite is strongly peraluminous. Normative corundum lies between 4% and 10% and varies inversely with increase in SiO 2 . The CaO content is typically low (<1.25%) and shows little variation; similarly the LILE show a limited range. On many variation diagrams, linear trends from peraluminous granulites to the Layos Granite and associated leucogranite can be observed. The chemical characteristics argue against an igneous fractionation or fusion mechanism for the diversification of the Layos Granite. A restite unmixing model between a granulitic pole (represented by the granulites of the Toledo Complex) and a minimum melt (leucogranites) could explain the main chemical variation of the Layos Granite. Melting of a pelitic protolith under anhydrous conditions (biotite dehydration melting) could lead to minimum-temperature melt compositions and a strongly peraluminous residuum. For the most mafic granites (61–63% SiO 2 ), it is estimated that the trapped restite component must have been around 65%. This high proportion of restite is close to the estimated rheological critical melt fraction, but field evidence suggests that this critical value has been exceeded. This high restite component implies high viscosity of the melt which, together with the anhydrous assemblage of the Layos Granite and the associated leucogranites, indicates H 2 O-undersaturated melting conditions. Under such conditions, the high viscosity magma (crystal-liquid mush) had a restricted movement capacity, leading to the development of parautochthonous plutonic bodies.