Evidence of Three Geodynamic Pulses From NeoProterozoic Sudan

The Neoproterozoic evolution of the central-eastern Bayuda Desert (Sudan)

Authors:

David Evuk, Gerhard Franz, Dirk Frei and Friedrich Lucassen

Abstract:

In the central-eastern Bayuda Desert (Sudan), a border area between the Saharan Metacraton and juvenile Pan-African crust of the Nubian Shield, the Rahaba-Absol and the Abu Harik-Kurmut Terranes were amalgamated along suture and shear zones. U-Pb zircon ages by laser-ablation dating of metamorphosed granitoid rocks reveals ages interpreted as magmatic and metamorphic activities throughout the Neoproterozoic. The meta-granitoids are calc-alkaline porphyroblastic varieties of biotite metagranite (969 ± 5 Ma), quartzfeldspathic metagranite (914 ± 6 Ma), biotite-muscovite metagranite (912 ± 4 Ma) and coarse-grained meta-monzodiorite (909 ± 9 Ma, 818 ± 19 Ma, 669 ± 13 Ma) associated with the Rahaba-Absol Terrane, and medium-grained metagranites (813 ± 4 Ma, 808 ± 5 Ma, 799 ± 16 Ma), a meta-quartz-monzonite (810 ± 10 Ma), biotite metagranites (794 ± 15 Ma, 783 ± 13 Ma, 700 ± 7 Ma), alkali metagranite (645 ± 5 Ma), and porphyritic meta-quartz-monzonite (630 ± 4 Ma) associated with the Abu Harik-Kurmut Terranes. Th/U ratios of the zircon were used to distinguish between intrusion and metamorphic ages.

The Neoproterozoic ages are interpreted as geodynamic pulses: a pre-Pan-African event 1000-900 Ma characterized by metamorphism and magmatism ending with the known Bayudian Event (920-900 Ma) in the Rahaba-Absol Terrane; a cycle between 850 and 775 Ma of subduction-related magmatism and metamorphism with a peak around 825 to 800 Ma; the final collision of the Rahaba-Absol and Abu Harik-Kurmut Terranes began before 714 Ma and ended probably before 645 to 630 Ma, documented by discordant E-W trending alkali metagranites and NE trending porphyritic meta-quartz-monzonite respectively. Theses ages of discordant intrusions constrain the post-collisional horizontal movement along the southern Keraf Shear Zone between 630 to ~590 Ma. The existence of inherited zircon grains in some samples of Pan-African age indicated sedimentary activity contemporaneous with the island-arc magmatism and metamorphism. This was probably a period of extensive erosion of the earlier island arc material and later stacked crustal material after terminal collisional between the Abu Harik-Kurmut arc and the Rahaba-Absol continental terrane. Pb isotope data (feldspar, whole rock) and Sr isotopes corroborate the division into two terranes, the Rahaba-Absol Terrane as an old cratonic part of the Saharan Metacraton, and the Abu Harik-Kurmut Terrane as juvenile island-arc additions during the Pan-African