The Tachakoucht–Iriri–Tourtit arc complex (Moroccan Anti-Atlas): Neoproterozoic records of polyphased subduction-accretion dynamics during the Pan-African orogeny

A pioneer of Precambrian geology: Boris Choubert’s fit of the continents across the Atlantic (1935) and his insights into the Proterozoic tectonic structure of the West African Craton and adjacent areas

“…His boundary almost parallels the commonly accepted western and northern boundary of the WAC which is delineated by HP/LT metamorphic continental and oceanic arc relics in the Hoggar Iforas belt (Berger et al, 2014), the Bou Azzer ophiolite (the first fully described Precambrian ophiolite ever, see Leblanc, 1976, and Fig. 6), and several oceanic arc relics in the Anti-Atlas (Triantafyllou et al, 2016; but see the different interpretation of the northern margin of the WAC by Ennih and Liégeois, 2001 shown on Fig. 5).…”

Intra-oceanic arc growth driven by magmatic and tectonic processes recorded in the Neoproterozoic Bougmane arc complex (Anti-Atlas, Morocco)

“…1b). In the Sirwa window, gneissic oceanic arc remnants, namely the Tachakoucht and Tourtit gneisses, show comparable protolithic ages (∼745-730 Ma; Thomas et al, 2004;Triantafyllou et al, 2016) and similarly to the Bougmane case study, played the role of hosting units for subsequent arc-related magmatism (Triantafyllou et al, 2016). Intermediate magmas produced at this stage (cf.…”

“…A major tectonic and metamorphic episode (D1) strictly affected these IGN1 arc units and therefore, can be restricted in time between the youngest protolithic age dated around 730 Ma (Triantafyllou et al, 2016) and the oldest age of undeformed igneous rocks emplaced during the second magmatic event IGN2 around 700 Ma (D'lemos et al, 2006; this study). In the Sirwa window, this episode is responsible for the burying of Tachakoucht meta-andesites up to 8 kbar of pressure conditions and the southward thrust of back-arc ophiolitic sequence onto the old arc units mentioned above (Triantafyllou et al, 2016). This scheme is likely applicable to arc-related complexes from the Bou Azzer inlier with thrusting back-arc Aït Ahmane ophiolite onto the Bougmane-Tazigzaout and Bou Azzer Mine gneissic arc complexes to the south (Fig.…”

“…In this scheme, a larger-scale thermal event having affected the entire Bougmane complex seems less plausible. Although no intrusive rocks contemporaneous to the thermal resetting of rutiles have been found in the Bougmane intrusive unit (south of the Bou Azzer inlier), the 660-650 Ma age range is well known and constrained in the Pan-African oceanic arc igneous activity and marked by the emplacement of dioritic plutons within the Bou Azzer inlier (Inglis et al, 2005;D'Lemos et al, 2006;Walsh et al, 2012;Admou et al, 2013;Triantafyllou et al, 2016). We thus suggest that this third igneous event (IGN3) could have locally perturbed the thermal evolution of IGN2 rocks either due to large scale heat diffusion or to the presence of small hidden (not outcropping) diorites bodies at Bougmane.…”

“…However, direct structural and petrological observations in oceanic arc lower crust require access to exposed sections and only two Mesozoic occurrences are well characterized. Many intra-oceanic arc complexes are exposed in the Pan-African belt of West and North African continent (Dostal et al, 1994;Thomas et al, 2004;Berger et al, 2011;Triantafyllou et al, 2016), providing a unique opportunity to compare Neoproterozoic arc growth processes with Phanerozoic and active IOAS. The main purpose of this study is to investigate the crustal processes that drive the construction of IOAS during the Pan-African orogeny.…”