RT Journal Article
T1 Palaeostress and geotectonic interpretation of the Alpine Cycleonset in the Sierra del Guadarrama (eastern Iberian CentralSystem), based on evidence from episyenites
A1 González Casado, José Manuel
A1 Caballero Donoso, José María
A1 Casquet, César
A1 Galindo Francisco, Mª del Carmen
A1 Tornos Arroyo, Fernando
AB Several episodes of hydrothermal activity related to periods of fracturing and/or reactivation of previous structures tookplace from 300 to - at least - 100 Ma, in the Sierra del Guadarrama, which is part of the crystalline axis of the IberianHercynian Fold Belt (Central-Iberian Zone). One of these episodes led to the formation of episyenites, which arede-quartzified and alkalinized granites. Episyenite formation took place on a regional scale and in a short period (approx. at277 Ma). The episyenites were formed by the action of fluids at temperatures between 350°C and 650°C, at depths of about6.5 km, and in microfractured dilatancy zones developed under a regional extensional regime. These zones are crosscut bynormal faults, developed during the progressive deformation process accompanying the formation of the episyenites.The calculated regional palaeostress tensor has ~r I close to vertical and σ3 between NI0-20E and an average value of thestress ratio (Ф) of 0.19 [Ф = (σ2 - σ3)/(σ1 - σ3)]. Because σ1 is close to vertical the stress tensor is compatible with anextensional deformation field. The analysis also shows that most of the faults that slip under this stress field have an averagecoefficient of friction of 0.8.This extensional regime was probably accompanied by a regional thermal anomaly, as suggested by the high temperatureof the fluids involved, which are amagmatic. This thermo-tectonic episode is interpreted as representative of the generalizedextensional regime corresponding to the onset of the Alpine Cycle. The episode was preceded by a wrench-faulting event,equivalent to the Late Variscan event of Arthaud and Matte (1977), for which an age of - at least - 300-290 Ma isindicated by recent radiometric data. In its turn, this event was preceded by the regional extensional gravitative collapse ofthe Hercynian orogen. A correlation between evidence from the cover (stratigraphy and volcanism) and evidence from thebasement (hydrothermal alterations, dyke injection episodes and granitic magmatism) is attempted on the basis of newavailable radiometric data.
PB Elsevier Science B.V., Amsterdam
SN 0040-1951
YR 1996
FD 1996
LK https://hdl.handle.net/20.500.14352/56989
UL https://hdl.handle.net/20.500.14352/56989
LA eng
DS Docta Complutense
RD 7 may 2024