The Ouarzazate Supergroup and its plutonic keel: the relicts of an Ediacaran silicic large igneous province in North Africa

Abstract

Ouarzazate igneous rocks from Sidi Ifni, SW Morocco, define a >3 km thick pile of mostly pyroclastic falls and flows of rhyolitic and dacitic ignimbrite and tuff, underlain by co-magmatic granitoid plutons. These rocks formed during two closely spaced periods of magmatism dated to c. 595–585 and 575–560 Ma, with the majority of rocks comprised of ferroan alkali feldspar rhyolite, syenorhyolite or monzorhyolite. They can be divided into high and low heavy rare earth element types that discriminate as both volcanic arc and within-plate magma types. Coeval, but less common, mafic rocks consist of olivine-normative trachybasalt and basaltic trachyandesite. Temporal and compositional equivalents of the Ouarzazate volcanic and intrusive rocks crop out widely across North Africa and extend into the previously contiguous regions of NE North America. Collectively, these erupted/shallowly emplaced Ouarzazate-like rocks represent asthenospheric partial melts that are variably hybridized by additions from the lithospheric mantle and crust. The root cause of asthenospheric upwelling remains unknown, although the foundering of pre-collison subducted oceanic lithosphere may provide a plausible explanation. The vast geographical extent over which Ouarzazate-like igneous rocks are found, together with their composition and intra-plate setting, support the conclusion that these rocks represent the remnants of a late Ediacaran silicic large igneous province. Supplementary material: A tabulation of the geochronologic and geochemical datasets from Sidi Ifni is available at https://doi.org/10.6084/m9.figshare.c.5945756