Abstract

Granitoid plutons are common throughout the late Proterozoic basement complex of north-east Sudan, frequently accounting for 60% of the outcrop. Geological, petrological and isotopic studies indicate that two distinct types of granitic plutonism can be recognized. An older diorite to granodiorite assemblage was emplaced between c. 815 and 724 Ma and a younger predominantly alkali feldspar granite assemblage consisting of numerous discrete high level intrusions was emplaced between c. 717 and 555 Ma. These granitoids have a calc-alkaline character similar to the volcanic rocks of the basement complex to which they are spatially and temporally related. The geochemical and isotopic data suggest a destructive plate margin rather than a within-plate palaeotectonic association. It is suggested that the granitoids represent an evolutionary trend from early diorite to granodiorite intrusions emplaced above a late Proterozoic subduction zone to later, post-tectonic intrusions emplaced during a late stage of volcanic arc development. The magmas of the early granitoids were probably mantle-derived while the later post-tectonic intrusions may have been derived from magmas produced by partial refusion of the volcanic arc protolith.

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