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THÈME 3. DYNAMIQUE INTERNE
des Sciences
de la Terre
24e
Réunion
27-31 octobre 2014
Résumés de la RST2014
the Ceret gabbro, both located in the Roc the Frausa massif (eastern Py-
renees).
Zircons from both samples display core-rim features, with more
contrasting cathodoluminescence textures in the gabbro sample (non-
luminescent cores and luminescent rims. Ages in cores and rims are
also different in both rock types. In the tonalite, cores yield a mean age
of 314±2 Ma, and rims yield a mean age of 311±1 Ma. Composi-
tionally, the tonalite zircons show rough differences between cores and
rims, suggesting that both areas were originated in magmas with dif-
ferent chemical characteristics. The chemical composition differences
are more pronounced between core and rim from the gabbro. The non-
luminescent cores correspond to an early magmatic pulse that occurred
at 312±2 Ma. They grew from a more evolved magma where most of
the plagioclase had already crystallized, in accordance with the lower
values for Eu anomalies. The luminescent rims correspond to a second
pulse that took place at 307±4 Ma. They originated from a less evolved
magma where plagioclase had not completely crystallized, as suggested
by the lower Hf content and the shallower Eu anomaly. The absence
of meso- and microscopic evidence of physical mixing (mingling) sug-
gests that the mixture was complete ; therefore, the existence of these
two magmatic pulses is recorded only in zircon. In summary, zircon geo-
chemistry suggests a complex magmatic history for the Sant Llorenc-La
Jonquera suite and the gabbro Ceret stock. This history includes seve-
ral pulses of magma and mixing of magmas with different geochemical
characteristics. Moreover, the chemistry of zircon supports the previous
models stating that these two igneous bodies are geochemically diverse
and they belong to genetically distinct igneous suites produced in dif-
ferent levels of the lithosphere.
3.8.32 (p) Etude structural et métamorphique
du dôme gneissique du Canigou (Pyrénées
Orientales)
Benjamin Le Bayon1
1BRGM, Orléans
Le massif du Canigou est un dôme de foliation constitué d’un en-
semble d’orthogneiss reposant sur les micaschistes de Balatg et sur-
monté par la formation de Canaveilles d’âge fini-Protérozoique à Cam-
brien inférieur (Castineiras et al., 2008). Plusieurs modèles ont été
proposés pour la formation du dôme et de sa mise en place : (i) Modèle
de pli couché de style pennique (Autran et Guitard, 1969) plissant la
discordance entre un socle granitique cadomien et sa couverture sédi-
mentaire paléozoïque ; (ii) modèle de dôme extensif (Gibson, 1991) qui
permet d’expliquer le métamorphisme rétrograde pendant le développe-
ment de la foliation principale ; (iii) modèle d’Anticlinal de Nappe, avec
le fonctionnement d’un chevauchement hercynien majeur, à vergence
SW situé à la base des gneiss, définissant ainsi une nappe (Lagarde,
1978).
Plus tard, un âge ordovicien (475 Ma) (Deloule et al., 2002) a été obtenu
pour les orthogneiss du Canigou. Ce nouvel âge a permis d’invalider
le premier modèle et de proposer le modèle suivant : (iv) un laccolithe
intrusif dans la Formation de Canaveilles, (Barbey et al., 2001).
L’auteur présentera :
- Une étude structurale et pétrologique des gneiss du Canigou, du
contact avec les formations métasédimentaires environnantes réalisée
lors du lever de la carte de Prats de Mollo (1/50 000). Cette étude a
permis de mieux documenter le style, l’intensité, et la répartition de
la déformation au sein du dôme, et de mieux connaitre les conditions
métamorphiques lors de la formation de la foliation régionale et des
zones mylonitiques.
- Une nouvelle vue sur le contact tectonique du Puigmal. Avec la pré-
sentation de coupes détaillées réalisées dans le secteur de Nuria qui
constitue une zone clé pour la compréhension des différentes phases de
déformation.
A partir de ces nouvelles données, l’auteur vous proposera un modèle
géodynamique préliminaire pour l’exhumation du dôme du Canigou.
3.8.33 (p) Detrital zircons from the pre-Silurian
rocks of the Pyrenees : Geochronological
constraints and provenance
Aina Margalef Porcar1, Pedro Castiñeiras2, Josep Maria Casas3,
Marina Navidad2, Montserrat Liesa4
1Centre d’Estudis de la Neu i de la Muntanya d’Andorra, Institut
d’Estudis Andorrans, Sant Julià de Lòria, Andorre
2Departamento de Petrología y Geoquímica, Universidad Complutense
de Madrid, Madrid, Espagne
3Departament de Geodinàmica i Geofísica-Institut de recerca
GEOMODELS Universitat de Barcelona, Espagne
4Departament de Geoquímica, Petrologia i Prospecció Geològica
Universitat de Barcelona, Barcelona, Espagne
We have carried out for the first time a detrital zircon study in the eas-
tern Pyrenees (Andorra). The four samples selected are located in the
vicinity of the Upper Ordovician La Rabassa unconformity. Three of
them were sampled just below it, and correspond to quartzites interbed-
ded in the uppermost part of the Jujols Group, a rather monotonous,
1500 m thick, succession composed of a rhythmic alternation of sand-
stone, siltstone and argillite. The other sample was taken just above the
La Rabassa unconformity, from the Bar Quartzite Fm., located in the
uppermost part of the Upper Ordovician succession.
A total of 540 laser ablation ICP-MS U-Pb analyses were made, but 101
of them were discarded because of their discordance. The maximum de-
positional age for the Jujols Group samples based on the youngest detri-
tal zircon population is 478±5 Ma ; whereas for the Bar Quartzite Fm.
is 443±6 Ma (Late Ordovician-Early Silurian). All the samples show
very similar U-Pb age patterns. The main age populations correspond to
Cambro-Ordovician (480-510 Ma), Ediacaran (550-750 Ma), Tonian-
Stenian (850-1100 Ma), Paleoproterozoic (1.9-2.1 Ga) and Neoarchean
(2.45-2.65 Ga).
The absence of a Middle Ordovician age population suggests a lack of
sedimentation at this time and confirms the presence of an unconformity
at the base of the Upper Ordovician succession, already evidenced by
structural, stratigraphic and cartographic criteria. The similar age pat-
terns on both sides of the intraordovicic discordance implies that there
is no change in the source area of both series.
The obtained age patterns have also been compared with those from
other peri-Gondwanan terrains, such as Sardinia and NW Iberia. The
similarity with the Sardinian age distribution suggests that they could
share the same source area and they were paleogeographically related at
Ordovician times, that is, in front of the Arabian-Nubian Shield.
3.8.34 (p) New palaeobotanical data in the Lower
Carboniferous of the Eastern Pyrenees :
Implication for the aging of the Variscan
deformation
Sergi Trias1, Carles Martín-Closas1, Josep Maria Casas2
1Departament d’Estratigrafia, Paleontologia i Geociències Marines,
Universitat de Barcelona, Espagne
2Departament de Geodinàmica i Geofísica-Institut de recerca
GEOMODELS Universitat de Barcelona, Espagne
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