Geochemistry and U-Pb geochronology of the Neoproterozoic aluminous A-type granite in the south-western Tanzania: Implications to the Tonian geodynamic evolution of Southern Africa

Abstract

This study presents new insights on the Litembo granite, a 30 km wide pluton located south of the Ubendian Belt in the southern Tanzania, East Africa. Whole-rock geochemistry, U-Pb zircon geochronology, and the Rb-Sr isotope system were used to determine its geochemical composition, age, and origin, contributing to regional geological and geodynamic context. The granite is metaluminous to peraluminous, ferroan, and calc-alkalic with high concentrations of Sr, Rb, Ba, High Field Strength Elements (HFSE; e.g., Zr, Y, Nb, and Ta), and high Ga/Al ratios. The total Rare Earth Element (REE) concentrations of the granite range from 335 to 693 ppm, showing fractionated REE patterns in the chondrite-normalized spider diagram ((La/Yb)_CN = 9.40–15.41) and a negative Eu anomaly (Eu/Eu*; mean = 0.87). Primitive mantle-normalized spidegrams reveal negative patterns for Ti, Sr, P, Y, and Cs, along with enrichment in Large Ion Lithophile Elements (LILE; e.g. Rb and Ba). Geochemical features of the rock are akin to anorogenic (A-type) granites, implying formation of Litembo granite from a deep source melt, involving plagioclase, garnet, and amphibole and/or complex differentiation processes, under extensional tectonics. An initial ⁸⁷Sr/⁸⁶Sr ratio (∼0.7113) suggests evolved crustal origins, with a Rb–Sr imprecise age of about 658 ± 20 Ma. Laser ablation ICP-MS U-Pb zircon dating yields crystallisation ages of 737.1 ± 2.9 Ma and 730.1 ± 3.0 Ma, indicating emplacement between 730 and 740 Ma, followed thermal diffusion of Rb and Sr in the rock at about 660 Ma. These ages and compositional features align with the Tonian intraplate (alkaline and carbonatite magmatism) in southern Africa and support for a thermal event linked to Rodinia's breakup, preceding development of the Mozambique Belt.