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

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 TiO2 (0.70-1.41 wt %), and relatively high Al2O3 (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 epsilon Hf(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.