the iberian variscan orogen

C
H
A
P
T
E
R
1
THE IBERIAN
VARISCAN OROGEN
Aerial view of the tectonic repetition of limestone beds in
the Láncara Formation, Primajas duplex structure of the
Esla thrust (photo by J.L. Alonso)
Martínez Catalán, J.R.
Aller, J.
Alonso, J.L.
Bastida, F.
Rocks of Upper Proterozoic to Carboniferous age forming the Variscan or Hercynian orogen - crop out
widely in the western part of the Iberian Peninsula, in
what is called the Iberian or Hesperian Massif. These
deformed rocks, often metamorphosed and intruded
by different types of granitoids, were witness to the
great mountain range formed in the late Paleozoic,
basically in the Late Devonian and Carboniferous
(between 370 and 290 million years ago), by the
convergence and collision of two major continents:
Laurasia and Gondwana.
The Iberian Massif constitutes a geological framework
of global interest. It is unique due to the continuity of
its exposures and because it displays excellent records
allowing the analysis of continental crust features, the
tectonic, metamorphic and magmatic evolution of
orogens, and therefore provides enormously relevant
data about the lithospheric dynamics during the latest
Precambrian and the Paleozoic.
The Variscan orogen forms the basement of the
Iberian Peninsula and of most of western and central
Europe. A crustal basement is the result of an orogeny, that is, the consequence of a deep remobilization
of the continental crust caused by the convergence
of plates, and is associated to uplift and the creation
of relief. The Variscan orogeny is the name given to
the whole set of geological processes which deeply
modified the continental crust of western Europe and
the north and northwest of Africa during the Late
Paleozoic (Devonian-Permian). In its long period of
activity (approximately 80 million years), this orogeny
shortened and intensely deformed those sediments
deposited previously along vast continental margins,
remobilized the prior basement on which they laid,
generated a new crust by partial melting of the former,
added fragments of oceanic crust and mantle, eroded
and re-sedimented part of the newly formed crust,
and deformed the majority of the new sediments.
The importance of the Iberian Variscan orogen lies in its
location close to three big orogenic belts: Caledonian,
Variscan and Appalachian. Given the diversity and
quality of the outcrops, it is one of the key geological frameworks recording the latest Precambrian and
Paleozoic evolution of the planet, the deformation
and generation of structures at different levels of the
continental crust, the thermal history and the generation of granitoids, all within the context of an active
continental margin (latest Precambrian) and a continental collision (Variscan Orogen).
What crops out in the Iberian Peninsula from that
basement (Iberian Massif) is part of a much longer
orogenic belt, extending to the north and east through
Central Europe into Poland, where it is shifted by a
tectonic line known as Thornqvist Fault, and continuing towards south Asia.
On the opposite side, the belt extends along north
and northwest Africa parallel to the Atlantic margin.
However, the Atlantic did not exist when the belt was
14
Figure 1. Scheme showing the position of the Iberian
Peninsula in relation to the Appalachians and the
Caledonian and Variscan belts. Modified from
Neuman and Max (1989).
formed at the end of the Paleozoic. In its place, what
presently is North America (then part of Laurentia) went
around the Variscan orogen and a wide belt developed
along its eastern margin: the Appalachians.
Figure 1 shows a paleogeographic reconstruction of
the continental masses at the end of the Paleozoic.
It is noticeable how Iberia, the west of France and
the south of Great Britain used to occupy a key position within the Variscan belt, at the junction of the
three most important Paleozoic orogenic belts: the
Appalachians to the southwest, the Caledonides to the
northwest, and the Variscan to the northeast. Besides,
Iberia shares with west France a marked and striking
bend or curvature known as the Ibero-Armorican Arch
(Ribeiro et al., 1995).
The former reconstruction allows to infer the ultimate
cause of the orogeny, since a set of continental crustal
blocks are nearby but separated by orogenic belts. It is
thus clear that convergence caused the orogenic processes, and continental collision was the final result.
We are talking about the convergence of three large
tectonic plates: Laurentia (North America), Baltica
(Scandinavia, northern belt of Europe and Russia), and
Gondwana (Africa, South America, Antarctica, India
and Australia). The final result was the creation, by
the amalgamation of many continental masses, of a
supercontinent, in this case the last Pangea generated
by the continuing geodynamics of our planet.
Being such an old orogenic belt (its main development
finished 290 million years ago), it is to be expected
that the continental crust generated is already totally
balanced (thermally and isostatically), and the orogenic
reliefs should have completely disappeared. However,
M a r t í n e z C a t a l á n , J . R . – A l l e r, J - A l o n s o , J . L . a n d B a s t i d a , F.
Figure 2. Zonation of the Iberian Massif according to the subdivision proposed by Julivert et al. (1972). The red
lines mark the position of the sections in figure 3.
the subsequent history of the Iberian Peninsula originated new reliefs, and that is what makes the Iberian
Variscan orogen even more interesting.
As a matter of fact, the Iberian Peninsula did not even
exist at the end of the Paleozoic, but was a later result
of the separation of the African and Eurasian plates.
The Iberian crustal block ended up with Eurasia in the
first fragmentation (Middle Jurassic), but was later isolated in the Early Cretaceous with the opening of the
Bay of Biscay and the Pyrenean line, remaining at the
mercy of both plates’ dynamics from then onwards,
which began their convergence in the Paleocene and
mid Eocene. This convergence, which is still active,
deeply remobilized the Variscan basement in the Betic
Range, and with less intensity in the Pyrenees, Iberian
Range, Demanda Range, and several other modern
mountain ranges. Some of these mountain ranges
are aligned from east-northeast to west-soutwest
(Cantabrian Range, Ancares, Montes de León, Central
System and the Portuguese extension through Serra
da Estrela, Sierra Morena and many other minor
reliefs) reflecting the north-south convergence of the
African and Eurasian plates, and resulting in excellent
exposures of the Variscan basement.
For a better presentation of the most outstanding features of the Variscan orogen in the Iberian
THE IBERIAN VARISCAN OROGEN
Peninsula, the different areas of the Massif will
be described according to the scheme proposed
by Julivert et al. (1972) (Figure 2). The five zones
parallel and concentric to the Ibero-Armorican Arch
are: Cantabrian Zone, West Asturian-Leonese Zone,
Central Iberian Zone, Ossa-Morena Zone and South
Portuguese Zone.
The Galicia-Trás-os-Montes Zone of Farias et al. (1987)
has also been added, although it is not a belt of the
orogen but an allochthonous crustal block thrusted
over the Central Iberian Zone.
Figure 3 shows two schematic sections through the
Iberian Massif, representative of the northwest (Pérez
Estaún et al., 1991) and of the southwest (Simancas
et al., 2002) of the Iberian Massif. It can be noticed
that we are dealing with a belt with double centrifuge
vergence.
In the Iberian Massif there are several structures,
which due to their geological interest together with
the good exposure, have been chosen as Geosites:
The Esla River Thrust in the Cantabrian Zone, the
Mondoñedo Thrust in the West Asturian-Leonese
Zone, Sierra del Caurel in the Central Iberian Zone,
and the Cabo Ortegal Complex in the Galicia-trasos-Montes Zone (Figure 4).
15
Figure 3, above. Two schematic geological
sections across the Iberian Massif.
a) According to Pérez-Estaún et al. (1991).
b) According to Simancas et al. (2002).
The location of the section is marked in
figure 2.
Figure 4, left. Geosites described in the text:
1) Esla River Thrust. 2) Sierra del Caurel.
3) Mondoñedo Thrust. 4) Cabo Ortegal
Complex.
Figure 5, below. Esla River Thrust section
showing the main allochthonous units and
duplexes, according to Alonso (1985).
The Cantabrian Zone represents the Iberian Massif
foreland: an area of Paleozoic pre-orogenic sediments
with relatively small thickness. These are Cambrian to
Devonian shallow sea deposits, and display a wedging
towards the external part as well as some stratigraphic
discontinuities. This wedging is in part a result of
crustal uplift followed by erosion in the late Devonian,
and shows the change from a passive margin to
Variscan collision. This erosion was followed by basin
deepening in the earliest Carboniferous, followed by
synorogenic sedimentation.
16
The Cantabrian Zone is the most continental part
of the Paleozoic basin and a magnificent example
of foreland thrust belt. In addition, it displays an
extremely tight tectonic bend representing the core of
the Iberian-Armorican Arch.
Thin-skinned tectonics, the deformation style of the
outer crust, features in the Cantabrian Zone a sequential development of thrusts and associated folds, contemporaneous with the classic clastic wedges along
the front of major thrusts. It is also characterized by
M a r t í n e z C a t a l á n , J . R . – A l l e r, J - A l o n s o , J . L . a n d B a s t i d a , F.
Figure 6. Esla River Thrust in the Valdoré
tectonic window. The colored line shows the
thrust plane. On top of it: limestones of the
Láncara Fm, slates of the Oville Fm and
quartzites of the Barrios Fm (CambrianOrdovician). Below, Upper Devonian
limestones of the Portilla Fm and a thin
succession of Lower Carboniferous. To the left,
the layout of the Aguasalio syncline is
observed.
Figure 7. Esla River Thrust north of Valdoré. The
thrust (upper colored line) superimposes with
perfect parallelism Cambrian and Devonian layers.
Within the relative autochtonous, a thrust partially
repeats the calcareous succession of the Portilla Fm
(lower colored line).
deposits filling in piggy-back basins located over the
thrusted slabs (Marcos and Pulgar, 1982; Rodríguez
Fernández et al., 2002). The tectonic structure is further complicated by the arcuate bending of the belt,
which seems to be partially contemporaneous with
thin-skinned tectonics, according to structural data
(Pérez-Estaún et al., 1988).
As a consequence of Cenozoic Alpine uplift, the
Cantabrian Mountain Range displays magnificent
landscapes with outstanding calcareous massifs,
some of which are protected areas such as Montaña
de Covadonga (Picos de Europa) National Park, and
the natural parks of Somiedo and San Emiliano
Valley.
Several sites with panoramic outlooks allow to see
large structures such as the Esla Thrust (Figures 5, 6,
7 and 8), the front of the Ponga Thrust, and that of
the Picos de Europa Thrust, together with associated smaller structures such as duplexes, frontal imbrications and ramps (Alonso, 1987; Álvarez-Marrón and
Pérez-Estaún, 1988).
The Esla Thrust, in the province of León, has been
selected as a Geosite due to its magnificent outcrops
of sedimentary formations of early Cambrian to early
THE IBERIAN VARISCAN OROGEN
Carboniferous age, piled in a series of allochthonous
structures (Figure 5). Inside this thrust, the frontal and
internal areas of several minor thrust slabs and associated sheets can be studied, as well as the geometrical
relationships that the different thrust sheets and faults
show amongst themselves and with the bedding
(Figures 6 and 7).
There are wonderful examples of thrust overstep
geometries, of drape folds and associated fault propagation, and of frontal imbrications and duplexes,
such as those at Primajas, Pardaminos and Pico Jano.
The accumulated minimum shortening of all thrusts
cropping out in this region is considered to be slightly
above 92 km. Typical in this zone are the fault rocks
developed under low temperature conditions and
limited to a 1 to 2 meter thick band at the base of
the Esla Thrust, which concentrates the deformation
associated to the displacement, which is calculated to
be around 19 km (Alonso, 1985, 1987).
Synorogenic deposits are also very interesting,
abundant and well preserved, with ages between
Westphalian and Stephanian B (Figure 8). Their presence allows to date the emplacement of thrusts, as well
as the folds associated to the thrust and the reactivation of bedding as a flexure-folding surface. Five main
unconformities have been identified in the synorogenic
sediments, although not all of them are discrete and
some change laterally to progressive unconformities.
The first two are related to the emplacement of the
thrusts, whereas the remaining three are related to
thrust reactivation and to the re-compression of folds
associated to them (Alonso, 1985).
17
Figure 8. Syncline developed upon Stephanian
conglomerates (thin colored lines) in relation to a
reverse fault (thicker line) thrusting the limestones
of the Alba and Barcaliente formations (Mountain
Limestone). The fault is an example of flexural
sliding along the stratigraphic surface during
tightening of the Peña Quebrada syncline
(Alonso, 1985).
Figure 9. Interpretation of the seismic lines
ESCIN-1 and ESCIN-3.3, placed one next to the
other to show the large scale structure in this
part of the Iberian Massif, as it is deduced from
seismic reflection profiles. According to PérezEstaún et al. (1994) and Ayarza et al. (1998).
18
The West Asturian-Leonese Zone is a very important unit because of its tectonic significance in relation
to middle crust deformation problems and the dynamics of orogenic wedges, as well as for the study of the
origin of granitoids and their relation to the orogeny.
With regard to structural features, this zone forms a
slate belt, not only because that is precisely the most
frequent lithology, but also because it displays a wide
belt with vertical folds and steeply-inclined axial-plane
cleavage which curves in depth becoming asymptotically parallel to a slightly-tilted mid-crustal detachment,
and which may go across the whole crust.
The West Asturian-Leonese Zone is divided into two
domains: western and eastern. The eastern one,
called Navia and Alto Sil domain (Marcos, 1973),
is generally characterized by steeply-dipping folds and
cleavage, as well as by the ductile deformation of
greenschist facies, and includes some thrust-related
repetitions. The seismic cross section ESCIN – 3.3
(Figure 9) proves that the thrusts join at depth to (or
are crossed by) a basal detachment which ends rooted
M a r t í n e z C a t a l á n , J . R . – A l l e r, J - A l o n s o , J . L . a n d B a s t i d a , F.
at the Mohorovicic discontinuity much farther to the
west. The western one, called Mondoñedo Thrust
domain, also shows steep folding and cleavage,
although to the west the folds become recumbent
and faulted folds, while cleavages turn subhorizontal
and metamorphism increases.
The coastal section between Cudillero and Viveiro
estuary is extremely interesting in this area, as it offers
an almost continuous structural section with spectacular deformation structures (Bastida, 1980; Pulgar,
1980).
Uplifted areas also offer an excellent blend between
geology and landscape. The Oscos region of western Asturias, the Ancares Natural Park, and the granitic massifs of La Tojiza and the surroundings of
Viveiro, both north of Lugo province, deserve to be
mentioned.
The West Asturian-Leonese Zone, and the part of the
Central Iberian Zone adjacent to it in Galicia, were
key areas in the definition of the different types of
granitoids and their interpretation (Capdevila, 1969;
Capdevila et al.,1973). The oldest granitoids (Figure
10) are typically biotitic, frequently porphyritic, and
include diorites, tonalites, granodiorites and monzogranites. They are collectively called early granodiorites, and are rocks originated deep at the base of the
continental crust, with mantle contribution. Their
development was followed by mid-crustal melting
which generated peraluminous magmas of so-called
leucogranites or two mica granites.
Both the early granodiorite massifs and the leucogranites are syntectonic with ages between 350 and 305
Ma, broadly coinciding with Variscan deformation.
The most modern group of granitoids is formed by
a set of post-kinematic plutons (gabbros, tonalites,
granodiorites and monzogranites). In contrast to the
former, its emplacement is restricted to a short span
of 295-285 Ma, a magmatic pulse suggesting a single
cause which Fernández-Suárez et al. (2000) linked to
the delamination of the mantle lithosphere at the end
of the orogeny, and its replacement by a hotter asthenospheric mantle.
The Mondoñedo Thrust, and more specifically its
basal shear zone in the coastal area of the Lugo
province (Figure 11), has been selected as a Geosite.
Its Cambrian slate and quartzite outcrops show the
effects of tangential deformation of the second
Variscan deformation phase (Bastida and Pulgar,
1978; Bastida et al., 1986; Aller and Bastida, 1993).
Its interest stems from it being an exposure of the
internal and deeper area of a thrust slab emplaced
under ductile conditions in the beginning stages, and
fragile in the last stages. Spectacular meso- and microstructures are observed in a ductile shear zone related
to crustal thrusting, with a thickness between 3 and
3.5 km. Some medium-grade metamorphic foliations,
stretching lineations, and fault rocks developed under
a wide temperature range, can also be studied.
THE IBERIAN VARISCAN OROGEN
Figure 10. Granitic plutons of the Iberian Massif in
relation with Variscan deformation stages (according
to López Plaza and Martínez Catalán, 1987).
East-verging isoclinal folds are abundant and show a
strong scattering of their hinges, very often displaying
curved hinges and tight shapes belonging to sheath
folds (Figures 12a, b and c). Folds are also affected
by the development of a second axial-plane foliation
and by a stretching lineation striking between N 100
and 110º E. Boudinage structures are also common
affecting quartzites, as well as S-C structures, which
are particularly abundant in Upper Proterozoic rocks at
the base of Mondoñedo Thrust, showing an ESE trend
of displacement (Figure 12d). In addition, the basal
thrust crops out at Aureoura beach (As Areouras) and,
north of it, the autochtonous slab of the Mondoñedo
Thrust crops out in the tectonic window of Xistral
(Gistral), as a train of regular folds affecting the thick
homonymous quartzitic formation (Figure 12e).
The Central-Iberian Zone comprises the central part
of the Iberian Massif and is the widest of all the belts,
around 400 km in the centre of the massif (Figure 2).
The structure of the low metamorphic grade regions
in the upper crustal levels is well defined at the surface
by the Armorican Quartzite, which due to its resistance
to weathering and erosion forms lined up reliefs bordering the elongated synclines in the southern part of
this zone, such as Guadarranque, in Toledo, Cañaveral
(cropping out along Monfragüe Natural Park) and
San Pedro Range, in Cáceres, and Herrera del Duque,
19
Figure 11. Geological
cross section through
the northern part of
the Mondoñedo
Thrust in two
versions. The one
above shows
lithostratigraphic
units with folds and
major faults. The one
below shows regional
metamorphism
isogrades and main
areas of ductile shear.
The arrows point to
the motion direction
of the faults and
shears (according to
Martínez Catalán et
al., 2003).
Figure 12. Structures
associated to the basal
shear zone of the
Mondoñedo Thrust:
a) 2nd phase isoclinal folds showing hinge scattering. Cliff between Fazouro and Foz. b) Set of folds with folded
hinges and en échelon distribution; the stretching lineation is parallel to the pencil. Cliff north of Nois. c) Cross
section of a closed fold. Cliff south of Area Longa beach. d) S-C structures at the base of the Mondoñedo Thrust in
the SE limit of Areoura beach. The C surfaces (shear areas) dip around 30º to the east (left) and among them the S
surfaces (schistosity) show sigmoidal geometry. e) Anticline on Lower Cambrian quartzites of the Mondoñedo
Autochton, underneath the basal thrust. Cliff southeast of Burela.
20
M a r t í n e z C a t a l á n , J . R . – A l l e r, J - A l o n s o , J . L . a n d B a s t i d a , F.
between Badajoz and Ciudad Real. In the centre of
the zone, the Tamames and Peña de Francia synclines
crop out in the Batuecas Natural Park (Salamanca).
In the north (Galicia) and in the Central System, the
Armorican Quartzite also delineates those anticline
cores with outcrops of the Ollo de Sapo Formation, a
thick volcanic, subvolcanic and volcanoclastic sequence
of Tremadoc-Arenig age (Parga Pondal et al., 1964;
Díez Montes, 2006).
The generic name of Armorican Quartzite is used, by
analogy with the Armorican Massif (France), to refer
to a mostly quartzitic lithostratigraphic unit deposited
on a wide, stable and homogenous platform existing in the Early Paleozoic. These quartzitic facies with
Arenig (Lower Ordovician) trace fossils followed by a
slate formation with trilobites, are not only present in
the Central Iberian Zone, but also in other areas of the
Iberian Massif. These facies extend from West Africa
to Afghanistan, showing the enormous size of the
marine platform. The platform was part of a passive
continental margin, as inferred from the mostly shallow marine sedimentary facies and its extraordinary
continuity, as well as by the existence of synsedimentary normal faults. The Central Iberian Zone provides
a magnificent field to study deformation under low to
high metamorphic grade conditions. Low-grade metamorphism is the most widely represented, particularly
towards the south and southeast, in Extremadura and
Toledo Mountains, where anchimetamorphic conditions are frequent. High-grade metamorphic rocks
with extensive partial melting crop out within antiformal structures and a few domes, where a fast transition between metamorphic grades is often observed.
The transition of metamorphic zones is either thinned
or incomplete, so several of these domes have been
related to extensional detachments, for example in the
region of Salamanca (Escuder Viruete et al., 1994; Díez
Balda et al., 1995) and in Toledo (Hernández Enrile,
1991). The natural parks of Sanabria Lake, in Zamora,
and Arribes del Duero and Agueda, in Zamora and
Salamanca, offer excellent exposures of the deeper
structural levels of the range, similarly to Guadarrama
and Gredos Ranges, where the granitic outcrops are
also impressive.
Differing deformation trends are evident within this
zone, with a narrow northern domain with recumbent
folds, a wider middle domain with vertical folds and
usually not too tight (Díez Balda et al., 1990), and a
very narrow southern domain with recumbent folds
(Martínez Poyatos, 2002).
Sierra del Caurel (Serra do Courel in Galician language), in the southern province of Lugo, has been
selected as a Geosite representative of the great
recumbent folds, with spectacular views of the folds
affecting the Armorican Quartzite (Figures 13 and
14), formed during the first Variscan deformational
phase.
The geometry of the Sierra del Caurel folds, cropping
out in an area 43 km long and 12 km wide, can be
THE IBERIAN VARISCAN OROGEN
Figure 13. El Caurel syncline, folding towards the
Armorican Quartzite, on the eastern slope of the
Ferreiriño river.
Figure 14, below. 2nd order anticline in the hinge zone
of El Caurel syncline. The hinge is displayed by the
Armorican Quartzite (coloured lined marking the top).
At the summit of the relief, in the middle of the
picture, the quartzite of the reverse flank of El Caurel
Syncline.
reconstructed thanks to the splendid outcrop conditions (Matte, 1968). It consists of two structures
(Piornal anticline and Caurel syncline) with almost
horizontal axial plane folds in the northern half. Even
not being the biggest, these are the best outcrops of
recumbent folds in the northern Iberian Peninsula. The
anticline plunges to the south towards its roots. The
overturned limb common to both folds reaches 10 km
semi-wavelength in the central part, narrowing to the
east and west. The hinge of the anticline is curved,
varying between N100ºE and N160ºE from west to
east. The most spectacular views are from the Quiroga
to Seoane do Courel road (El Caurel syncline), at Alto
do Castro, and from Busto and Froxán.
The Ossa-Morena Zone is a key region to determine the significance of the Cadomian orogeny
(Neoproterozoic) and therefore to understand endPrecambrian plate dynamics and its continuation
into the Paleozoic. The location of the zone, in the
21
southern Iberian Massif (Figure 2) makes its structural
evolution and its magmatism essential to understand
Late Paleozoic dynamics. Places like Sierra Morena
offer a good combination of geology and landscape
all along the Aracena and Picos de Aroche Natural
Park, and its extension to the east through Sierra
Norte Natural Park.
that transcurrent faults may have in continental
deformation. The northern part of the zone is an
interesting Variscan suture which crops out along
southern Sierra Morena, most of it inside the Natural
Park of Aracena and Picos de Aroche. In Portugal, the
coastal sections of Baixo Alentejo and Algarve are
worth mentioning.
The combination of isotopic age and geochemical
data in the Ossa-Morena Zone supports its evolution
as an active margin followed by the scattering of the
peri-Gondwanan terrains. In fact, up to now, this is
the only zone in the Iberian Massif where ages of
Cadomian metamorphism have been obtained. These
ages span from 562 to 524 Ma (Blatrix and Burg,
1981; Dallmeyer and Quesada, 1992; Ochsner, 1993;
Ordóñez et al., 1997) and even if the youngest ones
may reflect late- to post-orogenic thermal events, the
earlier ones clearly show a latest Proterozoic dynamothermal metamorphism.
A set of basic rocks cropping out along the boundary
between the South Portuguese and Ossa-Morena Zones
is interpreted as a fragment of oceanic lithosphere
(Figure 3), represented by the Beja-Acebuches unit.
South of it, there is a Lower Devonian - Carboniferous
basement accretion prism, the Pulo do Lobo antiform (Munhá et al.,1986; Oliveira, 1990; Quesada et
al.,1994; Onézime et al., 2002). The rest of the South
Portuguese Zone comprises the Iberian Pyrite Belt, one
the most important volcanogenic polymetallic sulphide
deposits of the planet. The Pyrite Belt volcanism, even
if bimodal and dominated by intermediate and acid
facies dated in the Devonian-Carboniferous boundary (347-355 Ma; Quesada, 1999), suggests a relation
with a magmatic arc.
Cadomian or end-Proterozoic magmatism has been
identified in the West Asturian-Leonese and Central
Iberian Zones, but it is particularly well defined in the
Ossa-Morena Zone. Here, the geochemistry and ages
fit within a long evolution of 120 My, allowing to
identify several stages (Oschner, 1993): anorogenic rift
(620-590 Ma), early calcalkaline orogenic magmatism
(590-540 Ma), peraluminous orogenic magmatism
(530 Ma), late-orogenic calcalkaline (525-510 Ma) and
alkaline (500 Ma) magmatism, and post-orogenic rift
(490-470 Ma). The last synorogenic stages were contemporaneous to the detachment and separation of
the first peri-Gondwanan crustal fragments.
The northeast and southwest boundaries of the OssaMorena Zone are important geological structures, most
probably related with former plate boundaries. The
Beja-Acebuches ophiolite along the southwest margin represents an oceanic suture. Furthermore, there
are strong differences between the granitoids of the
Ossa-Morena Zone and those of the rest of the Iberian
autochton. The granitic massifs are usually of limited
extension (Figure 10), lack the typical big plutons of
the Central Iberian Zone, and include more abundant
basic rocks, which calls for a bigger mantle contribution. The southern vergence of Variscan structures in
the Ossa-Morena and South Portuguese Zones, and
the existence of a crustal suture, suggest subduction of
the oceanic lithosphere towards the north, underneath
the Ossa-Morena Zone, which also explains its early
magmatism. The Ossa-Morena Zone represents the
complex evolution of a continental margin during the
Late Paleozoic, although in this case it is not associated
to a context of Cordilleran orogeny or long-lived active
margin, but to the convergence and collision of two
large continental masses, Gondwana and Laurasia.
The South Portuguese Zone is the southernmost of
the Iberian Massif and holds some of the keys of
Variscan evolution. It is a thin-skinned thrust belt
and, from the point of view of orogenic evolution,
the zone is considered an example of the importance
22
The South Portuguese Zone displays a south-vergent
thin-skinned tectonic overthrust, that is, opposed to
that in the other structurally comparable belt, the
Cantabrian Zone. The genetic significance of these
two external zones of the Iberian Massif is different.
Whereas the Cantabrian Zone is a Gondwanan overthrust foreland belt, the South Portuguese Zone first
developed as a foredeep basin, and later as an accretionary complex, particularly in the northern part. The
subduction of oceanic lithosphere under the marginal
prism ended with the arrival of continental crust,
when a terrain, most likely peri-Gondwanan, forming
the basement underlying the South Portuguese Zone,
came under the accretionary prism and developed a
thin-skinned thrust belt on top of it.
The zone also features mostly sinistral transcurrent
shearing, and has been proposed to be
contemporaneous with tangential deformation.
The most abundant stretching lineations in the
Beja-Acebuches ophiolite are subparallel to the
amphibolite band (Crespo Blanc, 1991), although
the first movements of the ophiolites record the
convergent component (Onézime et al., 2002). This
suggests that amphibolite shearing represents the
transition from a ductile overthrust to a sinistral ductile
tear-fault. Some structures display the kinematics of
oblique convergence, but it is more common for the
deformation to undergo partitioning into convergent
and transcurrent components, each one creating its
own structures. Both situations point to transpression
(Sanderson and Marchini, 1984), a deformation
regime whose geotectonic significance is that of
oblique collision between the plate underneath the
thrust belt of the South Portuguese Zone, and the
Iberian autochthonous plate (Silva et al., 1990).
The Galicia-Trás-os-Montes Zone includes the allochthons of Cabo Ortegal, Órdenes and Malpica-Tui in
M a r t í n e z C a t a l á n , J . R . – A l l e r, J - A l o n s o , J . L . a n d B a s t i d a , F.
Galicia (Spain), and of Bragança and Morais in Trásos-Montes (Portugal), as well as a common underlying
thrust sheet which has been called the Schistose or
Parautochtonous Domain (Farias et al., 1987; Ribeiro
et al., 1990), although it would be more appropriate to call it Lower Allochthon. Due to the variety of
terrains comprised by the allochthonous complexes,
each with different origin and tectonometamorphic
evolution, this zone is a basic reference to understand
Paleozoic geodynamics. It is herein described at the
end of this chapter because of the exotic character of
the units, and because it does not fit the continuous
and concentric trend of the rest of the zones making
up the Iberian Massif (Figure 3).
THE IBERIAN VARISCAN OROGEN
The units of the allochthonous complexes are grouped
into basal, intermediate or ophiolitic, and upper units,
according to their structural position within the thrust
pile. Many of them have recrystallized under deep
Figure 15. Evolution of the peri-Gondwanan terrain
preserved in the upper allochthonous units, according
to Gómez Barrero et al. (2007), based upon the
reconstruction of continental masses and oceans by
Winchester et al. (2002). In the Silurian, the lapetus
ocean almost disappeared, whereas the Rheic ocean is
still very wide, although it is being subducted
between Gondwana and Laurentia.
23
Figure 16. Evolution of the Rheic ocean and the Variscan orogen according to Martínez Catalán et al. (2007).
conditions, and are thus representative of the lower
crust, and sometimes even of the underlying mantle.
The basal units represent the most external margin of
Gondwana, with magmatic evidence for Ordovician
rifting, and metamorphic evidence for early Variscan
subduction (Gil Ibarguchi and Ortega Gironés, 1985;
Pin et al., 1992; Arenas et al., 1995; Rodríguez Aller,
2005). Ordovician rifting continued with the separation
of a peri-Gondwanan terrain and the creation of oceanic lithosphere beneath the Rheic Ocean between the
terrain and the new border of Gondwana. Fragments
of oceanic lithosphere with different isotope ages are
present in the suture included in the Galicia-Trás-osMontes Zone, mostly linked to the Rheic ocean (Díaz
García et al., 1999; Sánchez Martínez et al., 2006,
2007; Arenas et al., 2007).
The evolution of the upper units indicates their multiple orogenic character, with a first deformation during
the Lower Ordovician and later recycling by Variscan
collision. The associated magma chemistry and meta24
morphic evolution of the upper units suggests a volcanic arc environment in the Early Ordovician (Abati et
al., 1999; Andonaegui et al., 2002; Fernández-Suárez
et al., 2002). It would be an arc developed along the
Gondwana margin, and its detachment would have
left behind a backarc basin which in time would have
evolved to generate the Rheic Ocean. Figures 15 and
16 show schematically, in a map and a section, a possible evolution of the plates and terrains involved in
Variscan collision, according to the interpretations by
Gómez Barreiro et al. (2007) and Martínez Catalán et
al. (2007), respectively.
The existence of only one oceanic domain between
Avalonia and Gondwana has been taken into consideration, although the evolution was undoubtedly
complex. The opening of this domain, called Rheic, was
already taking place while the convergence between
Avalonia and Laurentia closed the lapetus ocean in
the Early Ordovician. This convergence meant the first
Taconic orogenic event, 490-480 Ma ago, and ended
M a r t í n e z C a t a l á n , J . R . – A l l e r, J - A l o n s o , J . L . a n d B a s t i d a , F.
with the amalgamation of Avalon 480-430 Ma ago, that
is, between the Middle Ordovician and Early Silurian.
From the Middle Silurian on, deformation progressively
started to affect the peri-Gondwanan terrains and the
Gondwana margin itself. Apparently, an accretionary
prism developed on the margin of Laurentia following
the amalgamation of Avalonia (Figure 16). The GaliciaTrás-os-Montes Zone records the progressive incorporation onto the orogenic prism of a volcanic arc represented by the upper units, an imbricate pile of oceanic
lithosphere of variable ages, and the partial westward
subduction of the outermost margin of Gondwana,
represented by the basement units (Martínez Catalán et
al., 1997, 2007). The blocking of continental subduction in the late Devonian marked the transition to a
collisional regime. The subducted basal units were overthrusted onto the external platform of Gondwana in
the Early Carboniferous, and a sheet of sediments was
wedged underneath forming the Schistose Domain.
Later, intracontinental deformation gradually affected
more external areas of the orogen.
The fourth Geosite selected in the Iberian Massif is
the Cabo de Ortegal Complex, in the province of
La Coruña, as it is an excellent representative of the
THE IBERIAN VARISCAN OROGEN
Figure 18. Northern end of the eclogite belt of the
Cabo Ortegal Complex at Punta dos Aguillóns. This is
part of the allochthonous unit of La Capelada,
structurally the highest of the complex.
Figure 17. Geological map and cross section of the
Cabo de Ortegal complex based on Vogel (1967),
Marcos et al. (1984) and Arenas (1988).
25
Figure 19. Pictures of the Cabo de Ortegal Complex:
a) Recumbent fold syncline in the La Capelada Unit, with granulites of the Bacariza Fm in the core (grey)
surrounded by ultrabasic rocks (yellowish). The colored line marks the contact. Southwest of San Andrés de Teixido.
b) Closed shaped folds developed during the thrust which emplaced the catazonal units. Unit of Cedeira.
c) Shear area at Carreiro, north of Cedeira, limited by two surfaces dipping 45º. It represents the overthrust
separating the Cedeira Unit to the east (right), from the Purrido Unit to the west.
d) Detail of the upper limit of Carreiro shear, showing a thrust plane under which some folds can be observed.
e) Punta Candelaria (o Candieira). The lighter colored rocks are amphibolites, gneisses and ultrabasic rocks of the
shear area of Carreiro, while the darker rocks to the left are amphibolites of the Purrido Unit.
f) Pillow-lava breccias in the ophiolitic Somozas Mélange, the structurally lower unit of the Cabo de Ortegal
Complex. Southern part of the Ensenada de Espasante.
exotic terrains making up the Galicia-Trás-os-Montes
Zone. All the groups of allochthonous units are present
in this complex (Figure 17), and one of those units has
provided the oldest rocks in the Iberian Peninsula (1160
Ma; Sánchez Martínez et al., 2006). In addition, this
complex stands out for the quality of its exposures and
its spectacular landscapes. The estuaries of Cedeira,
26
Ortigueira and Espasante offer magnificent structural
sections, combined with the cliffs on both sides of the
cape (Figure 18) and with the outcrops of Sierra de la
Capelada.
The Cabo de Ortegal Complex includes a great exposure of two catazonal allochthonous units: a deeper
M a r t í n e z C a t a l á n , J . R . – A l l e r, J - A l o n s o , J . L . a n d B a s t i d a , F.
one, representative of the lower crust and the upper
mantle of a continent, and/or a volcanic arc, corresponding to a peri-Gondwanan terrain (Galán and
Marcos, 1997; Santos et al., 2002). These are the
Cedeira and La Capelada units (Marcos et al., 1984,
2002), cropping out within the core of a SW-NE
elongated synform with a size of 28 by 12 km. The
catazonal units are part of the upper part of the
allochthonous complexes, and consist of rocks which
underwent high pressure and high temperature metamorphism (Vogel, 1967; Mendía Aranguren, 2000).
They include granulites and eclogites structurally
overlying ophiolitic units representing fragments of
Paleozoic oceanic lithosphere (Figure 19), and basement units representative of the Gondwana margin.
These ophiolites and basement units crop out in an
imbricate zone, structurally emplaced at the base of
the complex, and include an area of tectonic mixture
known as the Somozas Mélange (Arenas, 1988). The
imbricate zone continues underneath, affecting the
Schistose Domain, which is here formed by a series of
sheets comprising metasedimentary and metavolcanic
rocks of Silurian and Ordovician age (Valverde-Vaquero
et al., 2005).
The whole set of the complex is key to reconstruct
the evolution of the Rheic Ocean. It probably includes
the largest eclogite exposure in the world, with highpressure metamorphosed basic rocks indicative of
subduction processes. Given the excellent exposure
conditions of the lower crust, the processes of burial
and exhumation in an orogenic cycle can be studied.
The Cabo Ortegal Complex is also a good example
of a deep allochthonous unit emplaced into an epizonal crustal domain. The structural sequence shows
a spectacular development of structures at all scales,
from recumbent folds, ductile shears and thrusts
(Figure 19), to microfolds, boudinage, porphyroclast
systems, lineations and foliations. It constitutes a
natural laboratory for fabric deformation ranging
from high pressure and temperature conditions to
greenschist facies.
The transpressive orogen in the southwest of the
Iberian Peninsula, from the Central Iberian Zone to
the South Portuguese Zone, displays peculiar features
in relation to the deeply transpressive nature (oblique
collision) under which it formed in the Late Paleozoic
(Ribeiro et al., 1990; Quesada, 1991). The reconstruction of this sector is essential to understand the vast
circum-Atlantic Paleozoic orogenic domain, presently
scattered in three continents (Europe, Africa and
America) with a triple junction among the three of
them located precisely in this Iberian southern section (Figure 1).
The spectacular Iberian-Armorican Arch (arcuate structure) is a first-rate imbricate structure of geological
units arched or bent around a sub-vertical axis located
to the east and with centripetal emplacement directions. The most external zones of the Iberian foreland
are located in the center of the arch (Cantabrian Zone),
with well-preserved Carboniferous synorogenic deposits. To the west, a complete section of the Variscan
Orogen consists of a piling of E-to-NE-vergent thrusts
including (from lower-eastern to upper-western), the
Cantabrian, West Asturian-Leonese, Central Iberian
and Galicia-Trás-os-Montes zones. The first three
represent progressively deeper units of the Paleozoic
continental margin of the Iberian plate, whereas the
fourth one comprises the allochthonous exotic complexes of Galicia-Trás-os-Montes. Towards the exterior
of the arch, there are two more areas, Ossa-Morena
and South Portuguese Zones, where transpressive
deformation may provide some clues about the formation of the arch itself.
The models proposed to explain the Ibero-Armorican
Arch are varied. One of them is that of strict oroclinal bending, with an initial rectilinear belt which later
became bent. A popular model is that of the indenter,
which suggests the presence of a rigid buttress out of
Gondwana which might have caused the orogen bend
during its collision with Laurentia (Matte and Ribeiro,
1975; Matte, 1986; Ribeiro et al., 1995).
Summing up, the Iberian Massif provides the keys to
understand the history of the circum-Atlantic domain
during the Late Proterozoic and the Paleozoic, particularly
with regard to the evolution of the northern margin of
Gondwana and the Rheic ocean. It also offers excellent
exposures and structures to study deformation mechanisms in a collisional orogenic belt at different depths,
particularly the large thrust at crustal and even lithospheric scale. It also turns out to be a paramount reference to understand the genesis of granitoids in orogenic
collisional contexts. Its importance also lies on the fact
that not many times a complete section including both
forelands of an old collisional orogen is found preserved.
The selected Geosites represent some of those keys but,
in addition, the Iberian Massif features two particularly
outstanding structural and tectonic characteristics: the
transpressive orogen of the peninsular southwest, and
the arcuate structure, very tight in the northwest, known
as Asturian Knee and Ibero - Armorican Arch at the level
of the Variscan orogenic belt.
THE IBERIAN VARISCAN OROGEN
27
REFERENCES
ABATI, J., DUNNING, G.R., ARENAS, R.,
DÍAZ GARCÍA, F., GONZÁLEZ CUADRA,
P., MARTÍNEZ CATALÁN, .J.R. and
ANDONAEGUI, P. (1999). Early
Ordovician orogenic event in Galicia (NW
Spain): evidence from U-Pb ages in the
uppermost unit of the Ordenes
Complex. Earth Planet. Sci. Lett.,
165, 213-228.
ANDONAEGUI, P., GONZÁLEZ DEL
TÁNAGO, J., ARENAS, R., ABATI, J.,
MARTÍNEZ CATALÁN, J.R., PEINADO, M.
and DÍAZ GARCÍA, F. (2002). Tectonic
setting of the Monte Castelo gabbro
(Ordenes Complex, northwestern Iberian
Massif): Evidence for an arc-related
terrane in the hanging wall to the
Variscan suture. En: Martínez Catalán,
J.R., Hatcher, R.D., Arenas, R. and Díaz
García, F. (Eds.), Variscan-Appalachian
Dynamics: the Building of the Late
Paleozoic Basement, Geol. Soc. Am.
Spec. Paper, 364, 36-56.
ALLER, J. and BASTIDA, F. (1993). Anatomy of
the Mondoñedo Nappe basal shear zone
(NW Spain). J. Struct. Geol., 15,
1405-1419.
ALONSO, J.L. (1985). Estructura y
evolución tectonoestratigráfica de la
región del Manto del Esla (Zona
Cantábrica, NW de España).
Diputación Provincial de León, Inst. Fray
Bernardino de Sahagún, 276 p.
ALONSO, J.L. (1987). Sequences of thrust
and displacement transfer in the
superposed duplexes of the Esla Nappe
Region (Cantabrian Zone, NW Spain).
J. Struct. Geol., 9, 969-983.
ÁLVAREZ-MARRÓN, J. and PÉREZ-ESTAÚN,
A. (1988). Thin-skinned tectonics in the
Ponga Region (Cantabrian Zone, NW
Spain). Geol. Rundsch., 77, 539-550.
ARENAS, R. (1988). Evolución petrológica
y geoquímica de la unidad alóctona
inferior del complejo metamórfico
básico-ultrabásico de Cabo Ortegal
(Unidad de Moeche) and del Silúrico
paraautóctono, Cadena Hercínica
Ibérica (NW de España). Corpus
Geologicum Gallaeciae, 4, 543 p.
28
ARENAS, R., RUBIO PASCUAL, F.J., DÍAZ
GARCÍA, F. and MARTÍNEZ CATALÁN,
J.R. (1995). High-pressure microinclusions and development of an
inverted ­m etamorphic gradient in the
Santiago Schists (Ordenes Complex,
NW Iberian Massif, Spain): evidence
of subduction and syn-collisional
decompression. J. m
­ etam. Geol.,
13, 141-164.
ARENAS, R., MARTÍNEZ CATALÁN, J.R.,
SÁNCHEZ MARTÍNEZ, S., DÍAZ GARCÍA,
F., ABATI, J., FERNÁNDEZ-SUÁREZ, J.,
ANDONAEGUI, P. and GÓMEZBARREIRO, J. (2007). Paleozoic ophiolites
in the Variscan suture of Galicia
(northwest Spain): distribution,
characteristics and meaning. En: Hatcher,
R.D., Jr., Carlson, M.P., McBride, J.H. and
Martínez Catalán, J.R. (Eds.), 4-D
framework of continental crust.
Geo.l Soc. America Mem., 200.
AYARZA, P., MARTÍNEZ CATALÁN, J.R.,
GALLART, J., DAÑOBEITIA, J.J. and
PULGAR, J.A. (1998). Estudio Sísmico de
la Corteza Ibérica Norte 3.3: a seismic
image of the Variscan crust in the
hinterland of the NW Iberian Massif.
Tectonics, 17, 171-186.
BASTIDA, F. and PULGAR, J.A. (1978). La
estructura del Manto de Mondoñedo
­entre Burela and Tapia de Casariego
(Costa Cantábrica, NW de España).
Trab. Geol. Univ. Oviedo, 10, 75-124.
BASTIDA, F., MARTÍNEZ CATALÁN, J.R. and
PULGAR, J.A. (1986). Structural,
­metamorphic and magmatic history of
the Mondoñedo nappe (Hercynian belt,
NW Spain). J. Struct. Geol.,
8, 415-430.
BLATRIX, P. and BURG, J.P. (1981).
40Ar/39Ar dates from Sierra Morena
(Southern Spain): Variscan
metamorphism and Cadomian Orogeny.
Neues Jahrb. Mineral. Monatsch., 10,
470-478.
CAPDEVILA, R. (1969). Le métamorphisme
régional progressif et les granites dans
le segment hercynien de Galice nord
oriental (NW de l'Espagne). Thesis,
Université de Montpellier. 430 p.
CAPDEVILA, R., CORRETGÉ, L.G. and
FLOOR, P. (1973). Les granitoïdes
varisques de la Meseta Ibérique. Bull.
Soc. Géol. Fr.,
15, 209-228.
CRESPO BLANC, A. (1991). Evolución
­geotectónica del contacto entre la
Zona de Ossa-Morena y la Zona
Surportuguesa en las sierras de
Aracena and Aroche (Macizo Ibérico
meridional): un contacto mayor de la
Cadena Hercínica Europea. Fac.
Ciencias, Granada, 328 p.
DALLMEYER, R.D. and QUESADA, C.
(1992). Cadomian vs. Variscan evolution
of the Ossa-Morena zone (SW Iberia):
field and 40Ar/39Ar mineral age
constraints. Tectonophysics, 216,
339-364.
DÍAZ GARCÍA, F., ARENAS, R., MARTÍNEZ
CATALÁN, J.R., GONZÁLEZ DEL
TÁNAGO, J. and DUNNING, G. (1999).
Tectonic evolution of the Careón
ophiolite (Northwest Spain): a remnant
of ­oceanic lithosphere in the Variscan
belt. J. Geology, 107, 587-605.
DÍEZ BALDA, M.A., MARTÍNEZ CATALÁN,
J.R. and AYARZA, P. (1995). Syncollisional extensional collapse parallel to
the ­orogenic trend in a domain of steep
tectonics: the Salamanca detachment
zone (Central Iberian Zone, Spain).
J. Struct. Geol., 17, 163-182.
DÍEZ BALDA, M.A., VEGAS, R. and
GONZÁLEZ LODEIRO, F. (1990). CentralIberian Zone. Autochthonous Sequences.
Structure. En: Dallmeyer, R.D. and
Martínez García, E. (Eds.), Pre-Mesozoic
Geology of Iberia, Springer-Verlag,
Berlín, 172-188.
DÍEZ MONTES, A. (2006). La Geología del
Dominio "Ollo de Sapo" en las
comarcas de Sanabria and Terra do
Bolo. Tesis Doctoral, Universidad de
Salamanca, 496 p.
ESCUDER VIRUETE, J., ARENAS, R. and
MARTÍNEZ CATALÁN, J.R. (1994).
Tectonothermal evolution associated with
Variscan crustal extension in the Tormes
Gneiss Dome (NW Salamanca, Iberian
Massif, Spain). Tectonophysics,
238, 117-138.
FARIAS, P., GALLASTEGUI, G., GONZÁLEZLODEIRO, F., MARQUÍNEZ, J., MARTÍN
PARRA, L.M., MARTÍNEZ CATALÁN, J.R.,
MACIÁ, J.G. DE PABLO and RODRÍGUEZ
FERNÁNDEZ, L.R. (1987). Aportaciones
al conocimiento de la litoestratigrafía
and ­estructura de Galicia Central.
Memórias da Faculdade de
Ciências, Universidade do Porto, 1,
411-431.
M a r t í n e z C a t a l á n , J . R . – A l l e r, J - A l o n s o , J . L . a n d B a s t i d a , F.
FERNÁNDEZ-SUÁREZ, J., GUTIÉRREZALONSO, G., JENNER, G.A. and
TUBRETT, M.N. (2000). New ideas on the
Proterozoic-Early Paleozoic evolution of
NW Iberia: insights from U-Pb detrital
zircon ages. Precambrian Research,
102, 185-206.
FERNÁNDEZ-SUÁREZ, J., CORFU, F., ARENAS,
R., MARCOS, A., MARTÍNEZ CATALÁN, J.
R., DÍAZ GARCÍA, F., ABATI, J. and
FERNÁNDEZ, F. J. (2002). U-Pb evidence
for a polyorogenic evolution of the
granulitic-eclogitic units of the NW Iberian
Massif: Contr. Mineral. Petrol.,
143, 236-253.
FRANKE, W. (1989). Tectonostratigraphic
units in the Variscan belt of central
Europe. En: Dallmeyer, R.D. (Ed.),
Terranes in the Circum-Atlantic
Paleozoic Orogens. Geol. Soc. Am.
Spec. Paper, 230, 67-90.
GALÁN, G. and MARCOS, A. (1997).
Geochemical evolution of high-pressure
mafic granulites from the Bacariza
formation (Cabo Ortegal complex, NW
Spain): an example of a heterogeneous
lower crust. Geol. Rundsch.,
86, 539-355.
GARCÍA-CORTÉS, A., RÁBANO, I.,
LOCUTURA, J., BELLIDO, F., FERNÁNDEZGIANOTTI, J., MARTÍN-SERRANO, A.,
QUESADA, C., BARNOLAS, A. and
DURÁN, J. J. (2000). Contextos
geológicos españoles de relevancia
internacional: establecimiento,
decripción y justificación según la
metodología del proyecto Global
Geosites de la IUGS. Bol. Geol. Min.,
111-6, 5-38. Madrid.
GARCÍA-CORTÉS, A., RÁBANO, I.,
LOCUTURA, J., BELLIDO, F., FERNÁNDEZGIANOTTI, J., MARTÍN-SERRANO, A.,
QUESADA, C., BARNOLAS, A. and
DURÁN, J. J. (2001). First Spanish
contribution to the Geosites Project: list
of the geological frameworks established
by consensus. Episodes, 24 (2), 79-92.
GIL IBARGUCHI, I. and ORTEGA GIRONÉS,
E. (1985). Petrology, structure and
geotectonic implications of
glaucophane-bearing eclogites and
related rocks from the Malpica-Tuy (MT)
Unit, Galicia, Northwest Spain.
Chemical Geol., 50, 145-162.
GÓMEZ BARREIRO, J., MARTÍNEZ CATALÁN
J.R., ARENAS, R., CASTIÑEIRAS, P.,
ABATI, J., DÍAZ GARCÍA, F. and
WIJBRANS, J.R. (2007). Tectonic
evolution of the ­upper allochthon of the
Órdenes Complex (northwestern Iberian
Massif): structural constraints to a
polyorogenic peri-Gondwanan terrane.
En: Linnemann, U., Nance, R.D., Kraft, P.
and Zulauf, G. (Eds.), The evolution of
the Rheic Ocean: From AvalonianTHE IBERIAN VARISCAN OROGEN
Cadomian active margin to
Alleghenian-Variscan collision. Geol.
Soc. Am. Spec. Paper, 423, 315-332.
HERNÁNDEZ ENRILE, J.L. (1991). Extensional
tectonics of the Toledo ductile-brittle
shear zone, central Iberian Massif.
Tectonophysics, 191, 311-324.
JULIVERT, M., FONTBOTÉ, J.M., RIBEIRO, A.
and CONDE, L. (1972). Mapa Tectónico
de la Península Ibérica y Baleares
E. 1:1.000.000. Inst. Geol. Min.
España, Madrid, 113 p.
LEFORT, J.P. (1989). Basement Correlation
Across the North Atlantic.
Springer-Verlag, Berlín, 148 p.
LÓPEZ PLAZA, M. and MARTÍNEZ CATALÁN,
J.R. (1987). Síntesis estructural de
los granitoides hercínicos del Macizo
Hespérico. En: Bea, F., Carnicero, A,,
Gonzalo, J.C., López-Plaza, M. and
Rodríguez Alonso, M.D. (Eds.),
Geología de los granitoides and
rocas asociadas del Macizo
Hespérico, Rueda, Madrid, 195-210.
MARCOS, A. (1973). Las Series del
Paleozoico Inferior y la estructura
herciniana del occidente de Asturias
(NW de España). Trab. Geol., Univ.
Oviedo, 6, 1-113.
MARCOS, A. and PULGAR, J.A. (1982). An
approach to the tectonostratigraphic
evolution of the Cantabrian Foreland
thrust and fold belt, Hercynian Cordillera
of NW spain. Neues Jb. Geol. Paläont.
Abh., 163, 256-260.
MARCOS, A., MARQUÍNEZ, J., PÉREZESTAÚN, A., PULGAR, J.A. and BASTIDA,
F. (1984). Nuevas aportaciones al
conocimiento de la evolución
tectonometamórfica del Complejo de
Cabo Ortegal (NW de España). Cuad.
Lab. Xeol. de Laxe, 7, 125-137.
MARCOS, A., FARIAS, P., GALÁN, G.,
FERNÁNDEZ, F.J. and LLANA-FÚNEZ, S.
(2002). Tectonic framework of the
Cabo Ortegal Complex: A slab of lower
crust exhumed in the Variscan orogen
(northwestern Iberian Peninsula).
En: Martínez Catalán, J.R., Hatcher,
R.D., Arenas, R. and Díaz García,
F. (Eds.), Variscan-Appalachian
Dynamics: the Building of the Late
Paleozoic Basement, Geol. Soc. Am.
Spec. Paper, 364, 125-142.
MARTÍNEZ CATALÁN, J.R. (2006).
El orógeno varisco ibérico. Informe
final para el "Proyecto Global Geosites",
IGME.
MARTÍNEZ CATALÁN, J.R., AYARZA
ARRIBAS, P., PULGAR, J.A., PÉREZESTAÚN, A., GALLART, J.,
MARCOS, A., BASTIDA, F., ALVAREZ-
MARRÓN, J., GONZÁLEZ LODEIRO, F.,
ALLER, J., DAÑOBEITIA, J.J.,
BANDA, E., CORDOBA, D. and
COMAS, M.C. (1997). Results from
the ESCI-N3.3 marine deep seismic
profile along the Cantabrian
continental margin. Rev. Soc. Geol.
España, 8, 341-354.
MARTÍNEZ CATALÁN, J.R., ARENAS, R.,
DÍAZ GARCÍA, F. and ABATI, J. (1997).
Variscan acretionary complex of
northwest Iberia: Terrane correlation and
succession of tectonothermal events.
Geology, 25, 1103-1106.
MARTÍNEZ CATALÁN, J.R., ARENAS, R. and
DÍEZ BALDA, M.A. (2003). Large
extensional structures developed during
emplacement of a crystalline thrust
sheet: the Mondoñedo nappe (NW
Spain). J. Struct. Geol., 25, 1815-1839.
MARTÍNEZ CATALÁN, J.R., ARENAS, R.,
DÍAZ GARCÍA, F., GÓMEZ-BARREIRO, J.,
GONZÁLEZ CUADRA, P., ABATI, J.,
CASTIÑEIRAS, P., FERNÁNDEZ-SUÁREZ,
J., SÁNCHEZ MARTÍNEZ, S.,
ANDONAEGUI, P., GÓNZALEZ CLAVIJO,
E., DÍEZ MONTES, A., RUBIO PASCUAL,
F.J. and VALLE AGUADO, B. (2007).
Space and time in the tectonic evolution
of the northwestern Iberian Massif.
Implications for the comprehension
of the Variscan belt. En: Hatcher,
R.D., Jr., Carlson, M.P., McBride, J.H.
and Martínez Catalán, J.R. (Eds.), 4-D
framework of continental crust.
Geological Society of America
Memoir, 200.
MARTÍNEZ POYATOS, D. (2002). Estructura
del borde meridional de la Zona
Centroibérica and su relación con el
contacto entre las Zonas Centroibérica y
de Ossa-Morena. Lab. Xeol. Laxe, Nova
Terra, 18, 295 p.
MATTE, PH. (1968). La structure de la
virgation hercynienne de Galice
(Espagne). Revue Géol. Alp., 44, 1-128.
MATTE, PH. (1986). Tectonics and plate
tectonics model for the variscan belt of
Europe. Tectonophysics, 126, 329-374.
MATTE, P. and RIBEIRO, A. (1975).
Forme et orientation de l'ellipsoide de
déformation dans la virgation
hercynienne de Galice. Relations avec le
plissement et hypothèses sur la genèse
de l'arc ibero-armoricain. C. R. Acad.
Sci. Paris, 280, 2825-2828.
MENDIA ARANGUREN, M.S. (2000).
Petrología de la Unidad Eclogítica del
Complejo de Cabo Ortegal (NW de
España). Lab. Xeol. Laxe, Nova Terra,
16, 424 p.
MUNHÁ, J., OLIVEIRA, J.T., RIBEIRO, A.,
OLIVEIRA, V., QUESADA, C. and
29
KERRICH, R. (1986). Beja-Acebuches
Ophiolite: characterization and
geodynamic significance. Bol. Soc.
Geol. Portugal, 2, 1-31.
NEUMAN, R.B. and MAX, M.D. (1989).
Penobscottian-Grampian-Finnmarkian
orogenies as indicators of terrane
linkages. En: Dallmeyer, R.D. (Ed.),
Terranes in the Circum-Atlantic
Paleozoic Orogens. Geol. Soc. Am.
Spec. Paper, 230, 31-45.
OCHSNER, A. (1993). U-Pb
geochronology of the Upper
Proterozoic-Lower Paleozoic
geodynamic evolution in the OssaMorena Zone (SW Iberia): constraints
on the timing of the Cadomian
orogeny. Ph.D. Thesis, Univ. Zurich. Diss.
ETH, 10, 392, 249 p.
OLIVEIRA, J.T. (1990). South Portuguese
Zone. Stratigraphy and synsedimentary
tectonism. En: Dallmeyer, R.D. and
Martínez García, E. (Eds.), Pre-Mesozoic
Geology of Iberia, Springer-Verlag,
Berlín, 334-347.
ONÉZIME, J., CHARVET, J., FAURE, M.,
CHAUVET, A. and PANIS, D. (2002).
Structural evolution of the
southernmost segment of the West
European Variscides: the South
Portuguese Zone (SW Iberia). J. Struct.
Geol., 24, 451-468.
ORDÓÑEZ, B., GEBAUER, D. and EGUÍLUZ,
L. (1997). Late Cadomian formation of
two anatectic gneiss domes in the
Ossa-Morena zone: Monesterio and
Mina Afortunada. XIV Reunión de
Geología del Oeste Peninsular, Villa
Real, Portugal, Abstracts, 161-164.
PARGA PONDAL, I., MATTE, P. and
CAPDEVILA, R. (1964). Introduction à la
géologie de l'"Ollo de Sapo", Formation
porphyroide antesilurienne du Nord
Ouest de l'Espagne. Not. Com. Inst.
Geol. Min. España, 76, 119-153.
PÉREZ-ESTAÚN, A., BASTIDA, F., ALONSO,
J.L., MARQUÍNEZ, J., ALLER, J.,
ALVAREZ-MARRÓN, J., MARCOS, A.
and PULGAR, J.A. (1988). A thinskinned tectonics model for an arcuate
fold and thrust belt: The Cantabrian
Zone (Variscan Ibero-Armorican Arc).
Tectonics, 7, 517-537.
NW Spain from deep seismic reflection
profiling, Tectonophysics, 232, 91-118.
PIN, C., ORTEGA CUESTA, L.A., and GIL
IBARGUCHI, J.I. (1992). Mantle-derived,
early Paleozoic A-type metagranitoids
from the NW Iberian Massif: Nd isotope
and trace-element constraints. Bull.
Soc. géol. France, 163, 483-494.
QUESADA, C. (1991). Geological constrains
on the Paleozoic tectonic evolution of
tectonostratigraphic terranes in the
Iberian Massif. Tectonophysics,
185, 225-245.
QUESADA, C. (1999). Tectonostratigraphic
evolution of the Iberian Pyryte Belt.
Post-Conference Field Trip. XV Reunión
de Geología del Oeste Peninsular.
International Meeting on Cadomian
Orogens. J. Conf. Abstracts 4,
1032-1034.
QUESADA, C., FONSECA, P.E., MUNHÁ, J.,
OLIVEIRA, J.T. and RIBEIRO, A. (1994).
The Beja-Acebuches ophiolite (Southern
Iberia Variscan fold belt): Geological
characterization and geodynamic
significance. Bol. Geol. and Min.,
105, 3-49.
RIBEIRO, A., DIAS, R. and BRANDAO SILVA,
J. (1995). Genesis of the Ibero-Armorican
arc. Geodinamica Acta, 8, 173-184.
RIBEIRO, A., QUESADA, C. and
DALLMEYER, R.D. (1990). Geodynamic
evolution of the Iberian Massif. En:
Dallmeyer, R.D. and Martínez García, E.
(Eds.), Pre-Mesozoic Geology of
Iberia, Springer-Verlag, Berlín,
399-409.
RODRÍGUEZ ALLER, J. (2005).
Recristalización y deformación de
litologías supracorticales sometidas a
metamorfismo de alta presión (Complejo
de Malpica-Tuy, NO del Macizo Ibérico).
Lab. Xeol. Laxe, Nova Terra, 29, 572 p.
RODRÍGUEZ FERNÁNDEZ, L.R., FERNÁNDEZ,
L.P. and HEREDIA, N. (2002).
Carboniferous of the Pisuerga-Carrión
Unit. En: García-López, S. and Bastida, F.
(Eds.), Paleozoic conodonts from
Northern Spain, Cuadernos del
Museo Geominero, 1, Inst. Geol. Min.
España, 93-104.
PÉREZ-ESTAÚN, A., MARTÍNEZ CATALÁN,
J.R. and BASTIDA, F. (1991). Crustal
thickening and deformation sequence in
the footwall to the suture of the
Variscan Belt of northwest Spain.
Tectonophysics, 191, 243-253.
SÁNCHEZ MARTÍNEZ, S., JEFFRIES, T.,
ARENAS, R., FERNÁNDEZ-SUÁREZ, J.
and GARCÍA-SÁNCHEZ, R. (2006).
A pre-Rodinian ophiolite involved in the
Variscan suture of Galicia (Cabo Ortegal
Complex, NW Spain). J. Geol. Soc.,
163, 737-740.
PÉREZ-ESTAÚN, A., PULGAR, J.A., BANDA,
E., ALVAREZ-MARRÓN, J. and ESCI-N
Research Group. (1994). Crustal
structure of the external Variscides in
SÁNCHEZ MARTÍNEZ, S., ARENAS, R., DÍAZ
GARCÍA, F., MARTÍNEZ CATALÁN, J.R.,
GÓMEZ-BARREIRO, J. and PEARCE, J.A.
(2007). Careón Ophiolite, NW Spain:
30
Suprasubduction zone setting for the
youngest Rheic Ocean floor. Geology,
35, 53-56.
SANDERSON, D.J. and MARCHINI, W.R.D.
(1984). Transpression. J. Struc. Geol.,
6, 449-458.
SANTOS, J.F., SCHÄRER, U., GIL
IBARGUCHI, J.I. and GIRARDEAU, J.
(2002). Genesis of pyroxenite-rich
peridotite at Cabo Ortegal (NW Spain):
geochemical and Pb-Sr-Nd isotope data.
J. Petrology, 43, 17-43
SCOTESE, C.R. and McKERROW, W.S.
(1990). Revised World maps and
introduction. En: McKerrow, W.S. and
Scotese, C.R. (Eds.), Paleozoic
Paleogeography and Biogeography.
Geol. Soc. Mem., 12, 1-22.
SILVA, J.B., OLIVEIRA, J.T. and RIBEIRO, A.
(1990). South Portuguese Zone.
Structural outline. En: Dallmeyer, R.D.
and Martínez García, E. (Eds.),
Pre-Mesozoic Geology of Iberia.
Springer-Verlag, Berlín, 348-362.
SIMANCAS, F., GONZÁLEZ LODEIRO, F.,
EXPÓSITO RAMOS, I., AZOR, A. and
MARTÍNEZ POYATOS, D. (2002).
Opposite subduction polarities
connected by transform faults in the
Iberian Massif and western European
Variscides. En: Martínez Catalán, J.R.,
Hatcher, R.D., Arenas, R. and Díaz
García, F. (Eds.), Variscan-Appalachian
Dynamics: the Building of the Late
Paleozoic Basement, Geol. Soc. Am.
Spec. Paper, 364, 249-258.
VALVERDE-VAQUERO, P., MARCOS, A.,
FARIAS, P. and GALLASTEGUI, G. (2005).
U-Pb dating of Ordovician felsic
volcanism in the Schistose Domain of the
Galicia-Trás-os-Montes Zone near Cabo
Ortegal (NW Spain). Geológica
Acta, 3, 27-37.
VOGEL, D.E. (1967). Petrology of an
eclogite -and pyrigarnite- bearing
polymetamorphic rock Complex at Cabo
Ortegal, NW Spain. Leidse Geol. Med.,
40, 121-213.
WINCHESTER, J.A., PHARAOH, T.C. and
VERNIERS, J. (2002). Palaeozoic
amalgamation of Central Europe: an
introduction and synthesis of new results
from recent geological and geophysical
investigations. En: Winchester, J.A.,
Pharaoh, T.C. and Verniers, J. (Eds.),
Palaeozoic Amalgamation of Central
Europe. Geol. Soc. Spec. Publ.,
201, 1-18.
t íEnZe zC AT
C aAt aL lÁáNn,, JJ..RR.. -– AALl Ll eE r,
n sNoS,OJ,. LJ .. La. n-d BBAaSsTt Ii D
da
M AM
R Ta ÍrN
R , J J - - AAl Lo O
A,, F.
F