Petrogenesis and geodynamic setting of lamprophyres and related rocks in the South China continent: Insights from apatite U-Pb geochronology, Nd isotopes, and whole-rock major- and trace elements of diamond-bearing lamprophyre from Northern Guangxi P

Abstract Mantle-derived rocks provide a unique perspective for understanding Earth's interior and tectonic evolution. This study employs laser ablation–inductively coupled plasma–mass spectrometry U-Pb dating of apatite, in situ micro-area Nd isotope analysis, and comprehensive assessments of major- and trace elements in the Leidong minette of South China to elucidate its petrogenesis and geodynamic significance. The SiO2 content of Leidong minette ranges from 53.19 wt% to 55.08 wt%, classifying it as an intermediate magma. It is characterized by high concentrations of K2O (7.64–7.96 wt%), MgO (5.02–5.22 wt%), and K2O/Na2O(molar) ratios (21.22–23.41) indicating that it is an ultrapotassic rock. U-Pb isotopic analysis of apatite reveals an age of ca. 108 Ma, potentially in response to the retreat of the ancient Pacific subduction zone. The apatite 143Nd/144Nd (0.51198–0.51210) and (143Nd/144Nd)i (0.511780–0.511922) show slight variations, with relatively consistent εNd(t) (−14.0 to −11.2). The whole-rock samples show enrichment in large-ion lithophile elements, depletion in high field strength elements, and negative anomalies of Nb, Ta, and Ti. They also exhibit high Th/Yb (31.7–36.3) and Ta/Yb (1.1–1.2). These data, in conjunction with previously reported whole-rock Sr-Nd-Pb isotopic characteristics, suggest that the source of the Leidong minette is predominantly enriched mantle type II altered by fluid metasomatism from an ancient slab. The geophysical data and whole-rock geochemistry, with (Gd/Yb)N (5.0–5.3), support the hypothesis that the source region for the diamond-bearing minette was at depths of at least 100 km (~3 GPa). Regionally, the lamprophyres and related rocks (ca. 250–90 Ma) in central and northern Guangxi Province, China, represent an orogenic setting, primarily modified by subduction-related fluids, whereas the related rocks (ca. 490–438 Ma) in southeastern Guizhou Province are associated with an intraplate environment, influenced by melt enrichment. This indicates that the boundary between the western margin of the Cathaysia Block and Yangtze Craton may lie between these regions and their amalgamation time is not the late early Paleozoic but the Neoproterozoic. From the analysis of diamond ore-forming conditions, it appears that high-grade, large-scale diamond deposits are unlikely to have formed in the South China region.