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6. PROVENANCE OF THE HP-HT UPPER ALLOCHTHON
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The basal units of the allochthonous complexes are
formed by metasedimentary rock series with Edi-
acaran to Early Ordovician maximum depositional
ages (MDAs; Dıez Fernandez et al., 2010), intruded
by abundant calcalkaline ( c. 493 Ma) to alkaline –
peralkaline (c. 475–470 Ma) granitic bodies (Abati
et al., 2010; Dıez Fernandez et al. , 2012a). They
represent a continental terrane with Gondwanan
provenance, affected by high-P and low- to interme-
diate-T metamorphism during north directed Varis-
can subduction at c. 370 Ma (Gil Ibarguchi & Ortega
Girones, 1985; Arenas et al., 1995; Rodrıguez et al.,
2003; Abati et al. , 2010; Dıez Fernandez et al., 2011;
Lopez-Carmona et al. , 2014). This subduction took
place below ophiolites and other terranes previously
docked to the southern margin of Laurussia (Arenas
et al., 2014a).
The ophiolitic units are formed by mafic–ultramafic
rock series representing a varied ensemble of units
formed in different stages of the evolution of the
Palaeozoic oceans. Part of these ophiolites have been
interpreted as Cambrian remnants of the peri-Gond-
wanan oceans, including sequences stacked at the
base of a fore-arc (Sanchez Martınez et al. , 2012) and
back-arc sequences (Arenas et al., 2007). However,
the most extended ophiolitic units in NW Iberia, and
also along the Variscan suture in the rest of Europe,
are c. 395 Ma mafic–ultramafic rock series. The inter-
pretation of these units has changed over time. They
were first considered as supra-subduction zone ophio-
lites formed during the last stages of the closure of
the Rheic Ocean (Dıaz Garcıa et al. , 1999; Sanchez
Martınez et al., 2007). However, according to new
U–Pb/Lu–Hf zircon data, they have been recently
considered as related to the opening of a long pull-
apart basin, showing an interaction of the mafic
rocks with an old continental basement (Sanchez
Martınez et al. , 2011; Arenas et al., 2014a,b).
The Upper Allochthon (upper units) is located
above the ophiolitic units, and has been traditionally
interpreted as a unique terrane with continental crust
affinity. According to its tectonothermal evolution, it
is divided into HP– HT upper units (bottom member)
and IP upper units (top member). However, the
traditional interpretation of the upper units as a sin-
gle terrane can only be considered as preliminary, as
the final subdivision of the Upper Allochthon
depends on the provenance compatibility for both
metamorphic groups, which will be examined accord-
ing to the new data presented in this article.
The IP upper units, are composed of a thick silici-
clastic series with greywacke and pelitic members and
minor conglomerates (Dıaz Garcıa, 1990; Casti~neiras,
2005; Dıaz Garcıa et al., 2010; Fuenlabrada et al.,
2010), intruded by large massifs of arc-derived gab-
bros and granitoids (Andonaegui et al., 2002, 2012).
Their metamorphic grade varies from greenschist
facies to granulite facies conditions, with develop-
ment of extensive migmatization at the lowest levels
(Abati et al., 1999, 2003). The IP upper units’
tectonothermal evolution has a polymetamorphic
nature (Fernandez-Suarez et al. , 2002), with a first
Cambrian event connected with the evolution of a
peri-Gondwanan volcanic arc system (Abati et al.,
1999, 2007), and a second event related to a colli-
sional eo-Variscan activity (Gomez Barreiro et al.,
2006; Gonzalez Cuadra, 2007; Arenas et al. , in press).
The IP upper units in the Cabo Ortegal Complex are
only represented by the meta-siliciclastic Cari ~no
Gneisses (Vogel, 1967; Casti~ neiras, 2005), which have
been recently studied in terms of provenance (Albert
et al., 2015). The main conclusion is that the sedi-
mentary protoliths are clearly Gondwana derived,
with source areas located in the domain of the West
African Craton.
The HP–HT upper units are the bottom member
of the Upper Allochthon (located above the ophio-
lites) and they are mainly composed of ultramafic
rocks, mafic–intermediate high-P granulites, eclogites,
HT amphibolites, metagabbros, orthogneisses, abun-
dant migmatitic paragneisses and their retrogressive
products (Vogel, 1967; Gil Ibarguchi et al., 1990;
Peucat et al. , 1990; Abalos et al., 2003). The pro-
tolith ages for the meta-igneous rocks forming part
of these units range between 520 and 490 Ma, and
the age of the HP–HT metamorphism has been dated
to c. 400–390 Ma (Ordo ~ nez Casado et al. , 2001;
Fernandez-Suarez et al., 2007; Albert et al., 2013).
This HP–HT Middle Devonian tectonothermal event
was attained by a subduction process (Gil Ibarguchi
et al., 1999), which affected a continental or transi-
tional crust of unknown provenance.
In the Cabo Ortegal Complex, the metasedimen-
tary rocks of the HP–HT upper units are represented
by an eclogite facies gneissic formation described as
the Banded Gneiss formation (Fig. 1b). They out-
crop in the eastern sector of the Cabo Ortegal Com-
plex, with a ~ N20° trend and with thicknesses
varying between 175 m (North of Cari~ no) and
1300 m (Masanteo peninsula; Fig. 2). They are
formed by intensively deformed migmatitic psam-
mitic– pelitic gneisses with abundant lens-shaped and
variably retrogressed eclogite inclusions, with highly
sheared alternations of felsic igneous rocks (granitic–
tonalitic compositions), and rare inclusions of ultra-
mafic rocks and marbles. The mineral assemblages of
these lithologies were described by Vogel (1967).
REE patterns of the eclogitic lenses are similar to
those of N- and T-type MORBs (Peucat et al.,
1990). Pressure conditions for the eclogites of this
formation were calculated at ~23 kbar (Mendia
et al., 2001), with no clear evidence for development
of UHP metamorphism. However, UHP metamor-
phism has been described in a similar unit in the
French Massif Central (Lardeaux et al., 2001). The
objective of this article was the study of the prove-
nance of the para-derived eclogitic gneisses of this
formation. Comparison of the source areas of these
© 2015 John Wiley & Sons Ltd
962 R. ALBERT ET AL.