Publication: Tectonic evolution of a continental subduction‐exhumation
channel: Variscan structure of the basal allochthonous
units in NW Spain
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2011
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European Geoscience Union
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Abstract
A regional study starting from detailed geological mapping has been carried out in
the Malpica‐Tui Complex of Galicia in NW Spain. The complex is formed by two
units representing pieces of the external edge of Gondwana, subducted and exhumed
during the Variscan collision. The study shows that synsubduction and early
synexhumation structures in continental subduction channels tends to be obscured
and even erased once exhumation is complete. Detailed structural analysis, matched with
the knowledge of the history, and available data for other Galician basal units have
elucidated the major structures developed during the subduction‐exhumation process.
The results include evidence of the plate convergence causing early Variscan continental
subduction of the Gondwana margin. Subduction was followed by exhumation driven
by ductile thrusting within the subduction channel, which, in turn, provoked crustal
duplication in the subducted slab and modified the initial tectonometamorphic architecture
of the subduction wedge. The next step was accretion to the adjacent continental domains,
placing the subduction wedge on top of unsubducted parts of the Gondwana margin
via ductile thrusting. Thrusting was preceded by progressive propagation of a train of
recumbent folds toward the foreland that affected the previous structural stack. Subsequent
transference of oceanic (Rheic) and peri‐Gondwanan terranes to the Gondwana margin
took place by out‐of‐sequence thrusting followed by crustal extensional collapse and
strike‐slip tectonics