Geochemistry and petrogenesis of mafic microgranular enclaves (MMEs) in the bougaffer granitoid, Saghro inlier, eastern anti-atlas belt, Morocco

Abstract

Mafic Microgranular Enclaves (MMEs) within granitoids are commonly interpreted as indicators of coexisting mafic magma that were derived from the mantle, which can offer valuable insights into the origins and evolution of primary mafic magmas. In this article, we investigate the petrography and bulk-rock major and trace elements geochemistry of quartz monzonite, the hosted MMEs, and the associated pink granite, from the Bougaffer pluton in the eastern Saghro Inlier. This study aims to clarify the petrogenetic processes that formed the MMEs and their granitoid host rocks. The MMEs are characterized by a microgranular texture and occur as ellipsoidal, angular and rounded shape, ranging in size from 2 to 80 cm, with sharp boundaries. They share the same mineral content as their host rocks though in distinct proportions, and are classified as monzonite and monzodiorite with high-K calc-alkaline to shoshonitic composition. The MMEs show lower SiO₂ contents and higher TiO₂, CaO, MgO, Fe₂O₃t, and Al₂O₃ contents compared to their host granitoids. The MMEs and their host granitoid display several similarities, including the same mineralogy and similar total-rock compositions, suggesting a genetic relationship. The MMEs are most likely cumulates formed during the initial phase of the same magmatic system that produced the Bougaffer quartz monzonite. A two stages model is proposed, involving rapid solidification within the cogenetic host granitoid magma at the chamber boundaries, leading to the formation of crystal accumulations at the bottom of the magma chamber as cumulates. These cumulates were later fragmented and disturbed due to subsequent magma recharge and the convection induced within the magma chamber.