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Magmatism and early-Variscan continental subduction in the northern Gondwana margin recorded in zircons from the basal units of Galicia, NW Spain

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Abati Gómez, Jacobo y Gerdes, Axel y Fernández Suárez, Javier y Arenas Martín, Ricardo y Whitehouse, Martín J. y Díez Fernández, Rubén (2010) Magmatism and early-Variscan continental subduction in the northern Gondwana margin recorded in zircons from the basal units of Galicia, NW Spain. Bulletin de la Société géologique de France., 122 (1-2). pp. 219-235. ISSN 0037-9409

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Resumen

In situ uranium-lead dating (LA-SF-ICPMS
and SIMS) and Lu-Hf isotope analyses
(LA-MC-ICP-MS) of zircon from eclogite
facies rocks from the basal units of the
Variscan Belt in Galicia constrain their magmatic
and metamorphic evolution and give
some clues about the nature and origin of
the involved basement. The samples studied
are two felsic gneisses, two eclogites, and one
eclogitic gneiss of intermediate composition
(metatonalite). Oscillatory-zoned zircon cores
from the felsic samples gave a main clustering
of U-Pb ages at 493 ± 2 and 494 ± 2 Ma, and
some older ages that represent inherited cores.
Zircon grains from the intermediate and one
of the mafi c rocks show no inherited cores
and yielded ages of 494 ± 3 and 498 ± 6 Ma,
respectively, interpreted as time of protolith
crystallization. Variably developed homogeneous
zircon rims in one felsic gneiss
yielded an age of 372 ± 3 Ma, and very tiny
zircons of one eclogite gave 350 ± 2 Ma, both
of which we interpret as metamorphic ages.
The new age data demonstrate that the
calc-alkaline magmatic suite described in
the basal unit is ca. 20 Ma older than the alkaline
to peralkaline plutonic suite of the same
unit (dated at 472 ± 2 Ma; Rodríguez et al.,
2007), and thus probably represents a distinct
geologic event. Overgrowth rims are interpreted
as metamorphic on the basis of their
Lu/Hf and Th/U ratios. The 372 ± 3 age is
considered as dating the high-pressure (high-P)
metamorphism, and is essentially in agreement
with previous Ar-Ar and Rb-Sr data.
This high-P metamorphism marks the initial
early-Variscan subduction of the Gondwana
margin. The inherited zircon ages and Hf isotopic
composition of zircons point to a considerable
input of crustal material with West African
Craton provenance to the felsic magma.


Tipo de documento:Artículo
Palabras clave:Magmatism, Variscan, Gondwana margin, Galicia, NW Spain
Materias:Ciencias > Geología > Petrología
Código ID:26615
Depositado:04 Sep 2014 11:25
Última Modificación:04 Sep 2014 11:25

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