Paleoproterozoic granite chronology, geochemical characterization, and geological significance in the Longdu region of northeastern Zambia

The Longdu area in northeastern Zambia is located in the east-central part of the Bangweulu Block, where Paleoproterozoic granites are widely developed. These granites are critical for understanding the early Proterozoic tectonic evolution of the Bangweulu Block and the reconstruction of the Columbia Supercontinent. This study systematically investigates the granites through petrography, geochemistry, zircon U-Pb geochronology, and Hf isotope analysis. Results show that the main granites formed between 2019 ± 11 Ma and 1981.9 ± 8.6 Ma, while the late quartz diorite was intruded at 1961 ± 13 Ma. The early granites (calc-alkaline to high-K calc-alkaline, peraluminous to weakly peraluminous S-type) exhibit right-dipping rare earth element (REE) patterns, enrichment in large-ion lithophile elements (Rb, Th, U, K), depletion in high field strength elements (Ba, Sr, Ta, Nb), and negative Eu anomalies (δEu = 0.35–0.86). In contrast, the late quartz diorite (calc-alkaline to high-K calc-alkaline, quasi-aluminous S-type) displays high Sr, low Y/Yb/Cr/Ni, and weak positive Eu anomalies (δEu = 1.06–1.17), indicating partial melting under thickened crustal conditions. Zircon Hf isotopes reveal that the early granites have εHf(t) values of −6.2 to +5.0 and a two-stage model ages (tDM2) of 2992–2306 Ma, while the late quartz diorite shows εHf(t) = -5.5 to −0.6 and tDM2 = 2885–2639 Ma, reflecting compositional heterogeneity in magma sources derived from mixing of Archaean-Paleoproterozoic crust and mantle materials. High CaO/Na2O and low Rb/Sr ratios in the early granites suggest partial melting of sandy rocks, whereas low CaO/Na2O and Rb/Sr ratios in the late quartz diorite point to basaltic-felsic protolith melting. Integrated with regional and global tectonic evolution, the granites formed during the collision between the Tanzania Craton and the Bangweulu Block, representing a geological response to collisional orogeny linked to the assembly of the Columbia Supercontinent.