Publication: Upper crust reworking during gravitational collapse:
the Bembibre–Pico Sacro detachment system
(NW Iberia)
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Publication Date
2010
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Geological Society of London.
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Abstract
The kinematics of the basal allochthon in the SW of the O´ rdenes Complex is analysed to constraint
its evolution during collisional and postcollisional stages of the Variscan orogeny. Two distinct sequences have
been identified in the basal allochthon of this sector: the upper and lower sequences, in close correlation with
the subdivision of the basal allochthon in the Malpica–Tui Complex. Three main tectonic episodes have been
established in the basal allochthon: a high-pressure event related to continental subduction, a mesozonal event
of regional exhumation by thrusting and recumbent folding, and a regional-scale extensional episode that
resulted in the development of the Bembibre–Pico Sacro detachment system. The Bembibre–Pico Sacro
system rejuvenated pre-existing shear zones, whose weakness favoured the nucleation of the detachments.
Shear zones associated with the detachments overprinted the previous tectonic fabrics under conditions
ranging from lower amphibolite to greenschist facies, and with heterogeneously distributed ductile to brittle
deformation. The detachment system is coeval with late orogenic collapse and widespread magmatism, and
represents its upper crustal expression. It correlates with mid- and lower crustal flow and the development of
gneiss domes at depth in such a way that the basal allochthon can be considered a rheological boundary
between the more rigid allochthonous sequences above and the more viscous Schistose Domain and
autochthon below.