Mafic microgranular enclaves and magmatic fabrics in the Ediacaran granitoids of Saghro, Eastern Anti-Atlas: Insights into magma emplacement and tectonic evolution

Abstract

The Saghro inlier in the Anti-Atlas belt of Morocco comprises several granitoids dating from 600 to 550 million years ago (Ma), which are overlain by a volcano-sedimentary series. In particular, the granodioritic plutons exhibit widespread enclaves, which is a tool for emplacements mode and magma interaction processus during the Ediacaran evolution of the Anti-Atlas belt. This paper presents a detailed field mapping, petrographic analysis, and deformation quantification of the mafic microgranular enclaves (MMEs) and their host granitoids to characterize the emplacement mode of the plutons and the origin of MMEs.Macroscopically, the MMEs are rounded to ellipsoidal shapes and characterized by sharp, crenulated contacts, fine-grained textures, and some of them include fragments of host rock and feldspar xenocrysts. Petrographically, the MMEs exhibit a range of compositions from gabbroic to quartz diorite, and they are characterized by the presence of acicular apatite, quartz-feldspar ocelli, poikilitic and zoned plagioclases, which are the result of mixing/mingling of mafic and felsic magmas during the genesis of MMEs. The magmatic structures and enclave's organization in Saghro granitoids indicate two styles of emplacement. The c. 600 Ma Iknioun granodiorite exhibits an S-sigmoidal structure, representative of a syntectonic emplacement model within a transpressive dextral movement along E-W shear zones. While, in the 580-560 Ma Oussilkane, Tagmout, Igoudrane, and Bou Teglimt plutons, the organization of magmatic flow and orientations of enclaves suggest that the magma was emplaced as a post-tectonic dome. The variation in emplacement mode and the decrease in deformation intensity from the c. a. 600 Ma in the Iknioun pluton to the 580-560 Ma for the others plutons indicate a progressive shift in deformation regime from transpressive during the middle Ediacaran to a transtensive regime in the late Ediacaran, highlighting the progressive transition from Pan-African/Cadomian orogeny to Cambrian rifting.