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by the previous one, and the high intensity of
deformation tangles up structures, compositions
and any other primary features.
The high-grade studied terrain is a member
of the Cabo Ortegal Complex, which is one of
many complexes scattered along the European
continent. These complexes include the remnants
of the deepest sectors of the mountain chain that
sutured Pangea.They are huge nappe piles formed
and stacked during the orogen development,
disposed as big synformal structures. They can be
followed through the NWand SWIberianMassif,
the Armorican, Central, Vosges and Maures
Massifs and Corsica in France, the Bohemian
Massif in Germany, Poland, Czech Republic and
Austria, and the Alps and Sardinia in Italy.
Many theses and investigations have been
performed in the last decades, giving a high
degree of knowledge of the different units and
members of the Cabo Ortegal Complex. From
the basis of all this information, new studies
with modern techniques are required to clarify
and better understand the ages of protolith rock
formation, the igneous sources and the detrital
provenance of the different units involved in the
complex history of these old Variscan remnants.
For these reasons the present PhD was planned.
The Cabo Ortegal Complex is one of the
five complexes of NW Iberia. Two high-grade
terrains are found in this complex, the Basal
allochthonous units and the Upper Allochthon,
which are separated by an ophiolite belt. The
Upper Allochthon terrane is formed by an
intermediate-pressure (IP) top member and
a high-pressure and high-temperature (HP–
HT) bottom member, some of the formations
of which are the ones studied in this PhD. The
main formation studied is the Banded Gneisses,
which is a highly deformed metasedimentary
rock terrain with many lithologies included, and
from which no previous theses have been done.
To better understand the complex evolution of
this formation and to englobe it in its general
context, its two outlining formations have also
been investigated. They are the Cariño Gneisses
to the East and the Eclogite band to the West, and
both have been studied in previous PhD theses.
In this thesis, different methods have been
applied in order to constrain the origin and
evolution of the studied terrains. At first, a review
article is presented synthesising the geology of the
allochthonous terranes of Galicia (NW Iberia).
This work is the first article presented, which
has been recently submitted (chapter 3), and
represents a good introduction to the framework
of the issues addressed in the following chapters.
The first methods to be used had the objective
of recognising the objects to be studied, using
cartographic and petrographic techniques. The
results derived from applying these methods
are presented mainly in chapter 4. Afterwards,
and with the objective of knowing which are
the source areas of the detrital components of
the IP top member of the Upper Allochthon
(represented by the Cariño Gneisses), several
U–Pb, Lu–Hf and Sm–Nd isotopic experiments
were carried out. The results and interpretations
derived from this work are presented in chapter
5. These experiments were also carried out on
the HP–HT member of the Upper Allochthon,
to decipher which continental margin subducted
and therefore to make paleogeographic
reconstructions of the initial stages of continent
interaction of the Variscan orogenesis. These
experiments are described and discussed in
chapter 6. After having constrained the detrital
nature of these rocks, isotopic experiments were
carried out on the igneous rocks within two key
formations of the HP–HT Upper Allochthon, the
Eclogite Band andBandedGneiss formations.The
igneous rocks studied are; several leucosomes,
to study the features concerning partial melting
and regional foliation development of the high-
grade metasedimentary rocks; eclogites, to study
the nature of the mafic magmatic evolution and
the eclogite facies metamorphism attained; and
orthogneisses, to constrain the felsic activity of
an important magmatic arc system developed in
the initial stages of the Variscan orogen. All this
information is shown in chapter 7. To discuss
the complex collision between the two main
continents involved in the assembly of Pangea,
chapter 8 was drawn up, and an integrated
discussion of the PhD thesis is presented in
chapter 9.
1. INTRODUCTION
2