48 / 352
as correlatives (Sánchez Martínez
et al.
, 2007b).
The mafic rocks have typical compositions of
island-arc tholeiites, with slight Nb anomalies
(Sánchez Martínez
et al.
, 2007b) (Fig. 12b).
U-Pb zircon dating of a first sample of am-
phibolites provided a dominant group of zircons
with average age of
c.
1160 Ma, interpreted as
the age of the gabbroic protoliths. Minor zircon
populations with ages ranging 1.2-1.6 Ga were
considered as inherited crystals. Therefore, the
Purrido Ophiolite became an enigmatic pre-Ro-
dinian ophiolite preserved in the Variscan suture
(Sánchez Martínez
et al.
, 2006). Further research
in two amphibolite samples yielded a new, con-
sistent U-Pb zircon age of
c.
395 Ma, matching
the chronology of the Careón Ophiolite (Sánchez
Martínez
et al.
, 2011). Moreover, the Lu-Hf zir-
con data revealed the presence of Paleoprotero-
zoic isotopic sources mixed with juvenile mafic
material extracted at
c.
395 Ma (Fig. 14). The Sm-
Nd isotopic geochemistry of these amphibolites
also shows an important isotopic heterogeneity
for the original mafic material (Sánchez Martínez
et al.
, 2011). On the other hand, the Purrido am-
phibolites have a well-developed planolinear foli-
ation formed during the accretion of the unit and
dated at
c.
391.3 ± 6.6 Ma (
40
Ar/
39
Ar on horn-
blende Dallmeyer
et al.
, 1997).
The geochemical and geochronological data
obtained in the Purrido Ophiolite, can only be
interpreted in the context of interaction among
Devonian gabbroic magmas and continental
crust. Such scenario led to a rethinking of the
initial interpretation proposed for the Upper
Ophiolitic Units, according to which they would
be associated with the activity of an intra-Rheic
Ocean subduction zone. Again the new interpre-
tation will be presented and discussed in detail in
a later section.
Moeche Ophiolite
The Moeche Ophiolite crops out largely in the
eastern part of the Cabo Ortegal Complex (Fig.
3). The structural position relative to the Purrido
Ophiolite is not obvious, although they contact
in a small coastal section to the West of Cedeira
village, where the Moeche Ophiolite occupies a
lower structural position (Fig. 3). This ophiolite
32
3. GEOLOGICAL FRAMEWORK
Fig. 11.
(
a
) Synthetic column of the Careón Ophiolite showing the main lithologies and imbricates, distribution of
metamorphic facies, textures, levels where dynamic recrystallization of main components occurred, and the saw-tooth
thermal gradients developed during the earliest stages of thrusting. The U-Pb age of the gabbroic protholiths,
40
Ar/
39
Ar age
of hornblende in metamorphic soles and the peak P-T conditions reached during the accretion are also shown. Modified
from Díaz García
et al
., (1999a). (
b
) and (
c
) Representative columns for the Harzburgite (HOT) and Lherzolite (LOT) types
of ophiolites described by Nicolas (1989, 1995).