Antoine Triantafyllou: «Tracking intra-oceanic growth of a Neoproterozoic arc (Pan-African belt, Moroccan Anti-Atlas)»

Mercredi 24 Janvier 2018, 13:00 - 14:00
par Mickaël BONNIN

Relics of an intra-oceanic arc system are exposed in the Sirwa and Bou Azzer windows (Anti-Atlas mountain belt, southern Morocco). Both of these areas  form a highly tectonized patchwork made of a back-arc ophiolitic sequence to the north thrusted onto accreted arc complexes to  the south. These arc complexes (e.g., Tachakoucht, Tazigzaout and Bougmane complexes) are made of granodioritic gneisses and amphibolites with typical oceanic arc signature. Their protolithic igneous ages (U-Pb zircons) range from 750 to 730 Ma. These magmas were buried, deformed and metamorphosed under MP-MT conditions in Tachakoucht (700°C - 8 kbar) and HP-MT in Bougmane (750°C - 10 kbar) prior to several magmatic events dated at 700  and 650 Ma and the intrusion of hydrous basic magmas marked by poorly deformed igneous bodies (i.e. chilled hornblende gabbros, cumulative  hornblendites) with oceanic arc signatures. This episodic magmatism strongly perturbed the thermal regime of the arc leading to the granulitization of the host rocks at different levels of the arc crust and to the genesis of intermediate to felsic magmas (granodioritic to granitic). These ones have been segregated through the crustal section intruding both stacked paleo-arc and ophiolitic remnants. This field, petrological, geochemical and  geochronological study established that  oceanic arc magmatism in the Anti-Atlas occurred in three flare-ups on a 120 Ma long time span (760 to 640 Ma). The growth of the arc was controlled and  driven both by successive magmatic inputs  and intraoceanic tectonic thickening  processes while final collision of the intra-oceanic system with the West African Craton occurred later, around 630 Ma.

Lieu : Salle de réunion du bât. 9