Publication: Early Ordovician orogenic event in Galicia (NW Spain): evidence from
U–Pb ages in the uppermost unit of the Ordenes Complex
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Publication Date
1999
Authors
Dunning, Gregory R.
Díaz García, Florentino
González Cuadra, Pablo
Martínez Catalán, José Ramón
Andonaegui Moreno, Pilar
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Elsevier Science B.V., Amsterdam
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Abstract
New U–Pb data (zircon, monazite and rutile) obtained from rocks of the uppermost allochthon in the Variscan belt of
NW Spain indicate that the hangingwall to the suture includes an allochthonous unit with a pre-Variscan tectonothermal
evolution. This evolution is characterised by an Early Ordovician (498–500 Ma) bimodal magmatism followed almost immediately
(493–498 Ma) by a Barrovian style metamorphism up to the granulite facies. The metamorphism subsequent to
the igneous intrusions requires convergence and crustal thickening in order to generate the Barrovian facies pattern shown
by the lithologies of the uppermost allochthon. The almost coeval magmatism and metamorphism, and the chemistry of the
metabasites suggest an accretionary complex, probably related to a volcanic arc, as the most probable setting for the origin
of the uppermost unit. The implications of the existence of Early Ordovician convergent plate boundaries are discussed in
the context of Gondwana–Laurentia–Avalon interactions.