44 / 352
seem to confirm this interpretation (Arenas
et
al.
, 1995, 1997). The P-T-t path calculated for
the eclogites of the Agualada Unit is compatible
with underthrusting of a cooler slice, which in
this case would be represented by the Lamas de
Abade Unit and correlatives (Fig. 2).
The second deformation phase (D
2
) is related
to the initial exhumation of the subduction com-
plex. The current regional schistosity observed
throughout the Basal Units formed at this stage
(S
2
). S
2
is generally axial planar to large recum-
bent folds vergent to the East, which represent the
most prominent macroestructures in this terrane
(Fig. 10; Díez Fernández
et al.
, 2011). Fig. 10a
includes a map and cross section of the north-
ern part of the Malpica-Tui Complex, showing
the extensive development of the D
2
folds. The
largest recumbent fold is the Carrio Anticline,
in the Órdenes Complex, which is located above
the Lalín-Forcarei Thrust (Fig. 10b). This thrust
is responsible for the emplacement of the Basal
Units onto their relative autochthon and some of
its associated tectonic fabrics transect the large
recumbent folds transported at its hanging wall
(Martínez Catalán
et al.
, 1996).
The stretching lineation associated to S
2
shows
W-E to NW-SE trending, and consistent top-to-
the-E or -SE kinematics in present coordinates
(Gómez Barreiro
et al.
, 2010a; Díez Fernández,
2011). During D
2
the thermal inversion detected
in the Basal Units took place, both in the Órdenes
and the Malpica-Tui complexes. Heat transfer
from the overlying mantle wedge preserved in
the Campo Marzo Unit occurred during exhu-
mation and thinning of the subduction complex
(Fig. 2).
Exhumation of the Basal Units progressed via
the development of large extensional detach-
ments (D
3
). The Bembibre-Ceán Detachment
was active first, and then extension continued in
the Pico Sacro Detachment (Gómez Barreiro
et
al.
, 2010a; Díez Fernández
et al.
, 2012b) (Figs.
2 and 4). These detachments have associated
ductile-fragile fabrics and they can generate lo-
cal foliation (S
3
), even with mylonitic character.
Later tectonic activity in the Basal Units con-
sisted in the development of upright folds (D
4
).
The regional synforms that characterize the car-
tographic expression of the allochthonous com-
plexes were formed at this stage, in close relation
to large strike-slip shear zones that produced
intense local overprinting and reworking of pre-
vious low-angle faults and, ultimately, cut across
the upright structures. The Palas de Rei Shear
Zone, in between the Órdenes and Cabo Ortegal
complexes, and the Malpica-Lamego Shear Zone,
which forms the western limit of the Malpica-Tui
Complex (Llana-Fúnez and Marcos, 2001), were
generated during this phase of deformation (Fig.
2).
Ophiolitic Units
A classical Wilson Cycle considers that colli-
sional orogens typically contain a single ophiol-
itic belt, the only remnants of a sutured oceanic
domain. However, preservation of old N-MORB
oceanic lithosphere is problematic, as its thermal
structure favors its total consumption by subduc-
tion. Conversely, most of the ophiolites obducted
in orogenic belts were generated in supra-sub-
duction settings, either at the last stages during
the closure of large oceanic domains or in rela-
tion to the opening of ephemeral basins (Leitch,
1984; Pearce
et al.
, 1984). Ophiolitic belts related
to the opening of ephemeral pull-apart basins
have been specifically referred for the case of the
Rheic Ocean (Murphy
et al.
, 2011). Such oceanic
lithospheres is buoyant and tends to escape from
subduction, and can be easily obducted on conti-
nental margins. Since the nature of oceanic tracts
may vary along continental margins, oblique
continental convergence and collision may result
in the incorporation to the orogen of a collection
of oceanic sections with different origin and age.
Therefore, real geodynamic contexts lead to situ-
ations which tend to increase the variety of ophi-
olitic belts involved in large orogens, which rarely
contain a single ophiolite generated at a particular
time. This is also the case in the Variscan suture,
where several recent papers described a variety of
ophiolitic units with lithological and chronolog-
ical differences. Such diversity indicates variable
settings for the generation of oceanic lithosphere
during Paleozoic times, the understanding of
which seriously called into question the Variscan
and pre-Variscan paleogeographic reconstruc-
tions during the last years.
In the NW of the Iberian Massif, a group of
28
3. GEOLOGICAL FRAMEWORK