Petrogenesis and geodynamic setting of Ediacaran rocks from the Sirwa massif, Central Anti-Atlas of Morocco

The geodynamic evolution of the post-Pan-African Anti-Atlas Orogeny (∼ 650 Ma) remains debated, particularly regarding the basement beneath the Central Anti-Atlas and the geological processes leading to the formation of the Ediacaran Saghro Group (SG) and Ouarzazate Group (OG). New LA-ICP-MS U-Pb ages of 575 ± 3 Ma and 564 ± 2 Ma were obtained from two OG magmatic rocks. Detrital zircons from the SG yield a 2025 Ma maximum depositional age (MDA) and a prominent 2100 Ma peak, indicating exclusive recycling of Paleoproterozoic basement into the Ediacaran SG basin. Geochemically, two magmatic series are identified: (i) SG mafic rocks with a calc-alkaline, within-plate signature and negative Nb-Ta and Ti anomalies, consistent with a back-arc basin setting; and (ii) an OG felsic-intermediate, high-K calc-alkaline to shoshonitic series of post-collisional character. Isotope data ( ϵ Nd 620 = +3.2 to +4.6, TDM = 1.02–0.91 Ga for the SG; ϵ Nd 570 = −0.8 to +1.1, TDM = 1.30–1.15 Ga for the OG) indicate that the SG formed from a near-pristine mantle source with limited crustal input, whereas the younger OG involved significant reworking of older, evolved continental crust. These findings support a model in which early Ediacaran SG sediments and associated magmatic rocks were deposited in a back-arc basin. During this basin development, its shoulders were locally formed by the 2100 Ma Paleoproterozoic basement, supplying Paleoproterozoic zircons to the Saghro basin without interaction with Ediacaran sediments and corroborating the extension of the Eburnian basement north of the Anti-Atlas Major Fault (AAMF). The younger OG subsequently recorded a late Ediacaran post-collisional crustal collapse event, during which lithospheric delamination and potential slab break-off drove widespread crustal reworking and emplacement of a Silicic Large Igneous Province (SLIP).