Petrogenesis and tectonic implications of Tonian island arc volcanic rocks from the Gabgaba Terrane in the Arabian-Nubian Shield (NE Sudan)

Abstract

• The volcanic rocks in the Gabgaba Terrane were erupted during Tonian. • The volcanic rocks have positive εHf(t) values, indicative of derivation from a juvenile arc magmatism . • The depleted mantle source was metasomatized by slab-dehydration fluids. • The primitive magma was subjected to crustal assimilation prior to eruption. • The volcanic rocks were erupted during different stage of arc maturity. An integrated study of zircon U-Pb geochronology and geochemistry together with Lu-Hf isotopes, has been carried out on basaltic andesite and andesite from the Haweit area (Gabgaba Terrane, NE Sudan) to indicate their magmatic evolution. In-situ U-Pb zircon dating yielded a weighted mean age of 752 ± 11 Ma for andesite and 773 ± 17 Ma for basaltic andesite, suggesting they were generated during Tonian. The Haweit volcanic rocks are generally sub-alkaline and tholeiitic lavas. They are characterized by low Mg# (29–44), low TiO 2 (0.70–1.41 wt%), and relatively high Al 2 O 3 (14.60–18.30 wt%) indicating that they are not a primitive melt. The nearly flat REEs pattern of the basaltic andesites indicate that they were formed in an immature island arc setting. While andesites are slightly enriched in LREE and LILEs, suggesting more mature island arc setting. The calculated Hf-T DM C (0.87–1.6 Ga) ages of zircons preclude the possibility of interaction of the parental magma with a pre-Neoproterozoic crustal source. The low (La/Yb) N (0.73–9.56) and high Zr/Nb (33–62) ratios, along with positive εHf(t) values (+1.33 to +12.5) indicate that the Haweit volcanic rocks were originated from depleted mantle with little crustal contamination. The geochemical data suggest that the parent magma of the Haweit volcanic rocks could be formed by low degree partial melting of spinel‐bearing Iherzolite depleted mantle metasomatized by slab‐derived fluids. The Haweit andesitic melts were later subjected to crustal assimilation before the final eruption of lavas during two stages of arc evolution.