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ical composition but different record of high-P
metamorphism. The Capelada Unit occupies the
upper structural level, and developed eclogite fa-
cies metamorphism, whereas the Cedeira Unit
reached only granulite facies conditions. Anoth-
er possible third HP-HT unit has been also de-
scribed in the Cabo Ortegal Complex, the Peña
Escrita Unit (Fig. 3). This is a small lens-shaped
unit which crops-out at the South of the complex,
constituted by mafic rocks whose structure and
tectonothermal evolution are poorly constrained.
Consequently, it is not clear yet whether this is
a different unit or a section of either of the two
large HP-HT Capelada and Cedeira units.
The Capelada Unit is
c.
2000 m thick and,
from bottom to top contains ultramafic rocks,
high-P mafic granulites and eclogitic gneisses
and eclogites (Fig. 3). Its lithological constitution
and structure resembles that of an attenuated
mantle-crust transition. Taking into account the
age range of its protoliths (see below), this unit
may represent a section of a Cambrian back-arc
basin infilled with large amounts of terrigenous
sediments, now exposed in the upper structural
levels.
The eclogitic gneisses of the Capelada Unit
(Banded Gneisses, Figs. 3 and 24) are mainly
derived from semipelitic and greywackic sedi-
ments, and are intercalated with granitic and to-
nalitic orthogneisses (Albert
et al.
, 2012). These
gneisses are usuallly migmatised and show my-
lonitic foliation (Figs, 21e and 24). Mafic rocks
occur as numerous eclogite pods or bands with-
in the gneisses and also forming a thick layer of
eclogite separating this ensemble from the mafic
and ultramafic rocks underneath (Figs. 3 and 24).
In some sectors of that layer, pre-metamorphic
mingling processes are still recognizable (Fig.
21f), as well as some lenses of augengneiss simi-
lar to those observed in the IP Upper Units. Men-
dia (1996) described three main eclogitic types:
common eclogites, Fe-Ti eclogites after Fe-Ti
gabbros, and Al-Mg eclogites derived from troc-
tolitic gabbros. The high-P mineral assemblage
in the later (Grt+Cr-Omp+Qtz+Ky+Zo+White
mica+Rt) formed at
c.
23 kbar (Mendia, 1996).
The gabbroic protoliths of these eclogites were
dated at
c.
491-495 Ma (U-Pb in zircon; Ordoñez
Casado
et al.
, 2001; Albert
et al.
, 2013), while the
granitic protoliths of the orthogneisses yielded
ages of
c.
484-506 Ma (U-Pb in zircon; Albert
et al.
, 2013). On the other hand, U-Pb dating of
detrital zircons from the paragneisses reported
similar age populations to those obtained in the
Cariño Unit (IP Upper Units). Therefore, it is
considered that the source area for this sequence
was also located in North Africa (Albert
et al.
,
submitted).
The high-P granulites of the Capelada Unit
are referred as the Bacariza Formation (Fig. 3)
The dominant mafic members contain Grt+Cpx-
+Pl+Qtz+Zo-Czo+Hbl+Rt±Ky (Fig. 21c), al-
though other associated types with intermedi-
ate composition may be found (Puelles, 2004;
Puelles
et al.
, 2005). Extensive partial melting
and retrogression along with strong shearing
experienced during exhumation conferred a het-
erogeneous character to this formation (Figs. 21c
and 21d). The most common lithologies are a va-
riety of amphibolic gneisses, which preserve the
HP-HT mineral assemblage in less retrogressed
mafic lenses surrounded by a intense mylonitic
regional foliation (Fig. 21b). Given the absence
of metasedimentary rocks and the presence of
metaigneous types, probably derived both from
mafic and scarcer granitic protoliths, the most
probable precursor for the granulite formation
was a plutonic complex associated with a mag-
matic arc, which is in agreement with the back-
arc setting proposed for the whole Capelada Unit.
U-Pb zircon dating of a non-retrogressed mafic
granulite yielded an age of
c.
520 Ma, interpret-
ed as the chronology of the gabbroic protoliths
(Fernández-Suárez
et al.
, 2007).
The ultramafic rocks of the Capelada Unit
occur in three massifs, from North to South the
Limo, Herbeira and Uzal massifs (Figs. 3 and
21a). These are structurally connected and alto-
gether represent the largest ultramafic unit iden-
tified in the Variscan Belt. The thicker ultramafic
succession appears in the Herbeira Massif, be-
ing constituted by
c.
600 m of harzburgites and
dunites with many alternations of pyroxenites.
It has been interpreted as a section of a mantle
wedge above a subduction zone and it is con-
sidered as one of the world-class examples of a
heterogeneous upper mantle (Girardeau
et al.
,
1989; Girardeau and Gil Ibarguchi, 1991). Some
ultramafic layers contain chromitites enrich in
Pt-Pd (Moreno
et al.
, 2001). A Sm-Nd isochrone
48
3. GEOLOGICAL FRAMEWORK