216 / 352
200
7.6. General discussion
From the leucosome samples studied, it is
interpreted that a first migmatization of the
metasedimentary rocks took place at around
485–495 Ma. This process was probably triggered
by a temperature input related to the magmatic
arc system activity. These leucosomes were re-
melted at high-T conditions between 379 and
403 Ma, with a zircon crystallisation climax at
c.
388 Ma. This second event was most probably
related to the HP–HT Devonian metamorphic
event.
From the eclogite samples studied, it
is interpreted that the Devonian zircon
crystallisation climax was triggered by the
HP–HT metamorphic event at
c
. 393 Ma,
most probably near the metamorphic path
temperature peak. The Cambrian–Ordovician
eclogite population shows a zircon crystallisation
climax at
c
. 480 Ma and a relative abundance
peak at
c
. 505 Ma. Both ages are interpreted as
the ages of the protolith mafic generation, but
the possibility of a generation at
c
. 505 Ma and
a metamorphic event at
c
. 480 Ma cannot be
discarded or proved. The sources of the mafic
protolith rocks are varied. The protoliths are
juvenile, with an almost direct derivation from
a depleted mantle source, and they are also
isotopically enriched. These isotopically enriched
sources are interpreted as a partial fusion of
an enriched mantle component (probably the
subcontinental mantle of Gondwana), or as an
important contamination of a depleted mantle
partial melt with continental crust material.
From the orthogneiss samples studied,
it is interpreted that the Devonian zircon
crystallisation climax was triggered by the
HP–HT metamorphic event at
c
. 395 Ma. The
orthogneisses are the igneous lithologies that
were less affected by this HP–HT metamorphic
event. The Cambrian–Ordovician orthogneiss
population shows a zircon crystallisation
climax at 498 Ma with a long tail of ages down
to
c
. 460–470 Ma and a relative abundance
peak at
c
. 512 Ma. These ages are conservatively
interpreted as the ages of protolithic formation,
but a more complex evolution is also proposed.
The magmatic activity of the arc system started
at around 512 Ma and finished around 470–460
Ma, and this activity induced high–T related
metamorphism at around 498 Ma that partially
melted previously generated igneous rocks
within the same magmatic arc up to
c
. 460–470
Ma.
7.6. GENERAL DISCUSSION