Zircon U-Pb ages and Lu-Hf isotope systematics from late-tectonic granites, Geita Greenstone Belt: Implications for crustal growth of the Tanzania Craton

Granite plutons that intruded south of lake Victoria and north of the Geita Greenstone Belt have geochemical characteristics similar to high-K granites. When compared to the late high-K granites from the Musoma–Mara region, they have lower SiO2 content and higher TiO2, Al2O3, CaO, Na2O, P2O5, MgO and FeOt. They also show higher values for V, Sr, Zr, Ba and Hf concentrations. All samples display high total REE abundances (∑REE 139–393) and weak to moderate Eu depletion (Eu/Eu*: 0.25–0.77). Their chondrite-normalized pattern indicates that the light REE are moderately fractionated (3.03 < Lan/Smn < 6.24), whereas the heavy REE are weakly fractionated (1.63 < Gdn/Ybn < 2.80). The granite plutons are generally undeformed with 207Pb/206Pb ages between 2660 and 2620 Ma, and intruded after the main ductile deformation that affected the Geita Greenstone Belt. The 176Hf/177Hf ratios for zircons from all samples are identical within error suggesting evolution from an isotopically uniform reservoir. The ɛHf values plot along the CHUR evolution line indicating that the granite represents juvenile crustal melts derived from greenstone material. Available zircon ages from the Tanzania Craton suggest that crustal growth occurred in three distinct periods, 2850–2800 Ma, 2770–2730 Ma and 2700–2620 Ma, with the dominant period of crustal growth around 2700 Ma. Zircon ages from the Sukumaland and Musoma–Mara Greenstone Belts indicate that the greenstone sequences formed during the same three periods of crustal growth