Petrogenesis and tin endowment of the Late Mesoproterozoic and Neoproterozoic granites in the Mosuoying area, SW China

• Zircon U–Pb data identify two-pulse granitic magmatism in the area, represented by ca. 1049–1038 Ma (Late Mesoproterozoic) and ca. 842–836 Ma (Neoproterozoic) granites. • They are both peraluminous, with the former showing aluminous A-type affinity and the latter exhibiting differentiated S-type affinity. • The Late Mesoproterozoic granites were emplaced during continental rifting, while the Neoproterozoic granites were generated in association with oceanic subduction. • Tin mineralization genetically correlates with the Neoproterozoic highly evolved S-type granites. The Late Mesoproterozoic and Neoproterozoic granitic rocks are widespread in the southwestern (SW) Yangtze Block; however, their emplacement ages, petrogenesis, and tin endowment remain poorly constrained. The Mosuoying granitic batholith, which hosts the large-scale Chahe Sn deposit on its eastern periphery, is primarily composed of porphyritic biotite granite and medium- to fine-grained biotite/two-mica granite. The former constitutes the major exposure of the batholith, whereas the latter is sporadically exposed as stock. LA-ICP-MS U–Pb geochronology of zircon suggests that the porphyritic biotite granites crystallized at ca. 1049–1038 Ma, followed by the medium- to fine-grained biotite/two-mica granites at ca. 842–836 Ma. The Late Mesoproterozoic porphyritic granites have 67.90–73.73 wt.% SiO 2 , characterized by elevated Zr + Nb + Ce + Y concentrations (> 350 ppm), high 10,000 × Ga/Al ratios (> 2.6), and high magma temperatures (846–892 °C), exhibiting an A 2 -type granite affinity. Whole-rock geochemical and Nd–Hf isotopic compositions ( ε Nd (t) = −5.70 and −4.69, ε Hf (t) = −3.87 to +2.02, and T DM2 of 1.9–1.6 Ga) indicate that they probably originated from the partial melting of the Paleoproterozoic continental crust, with a minor contribution from the mantle. The Neoproterozoic medium- to fine-grained granites are silica- (73.55–75.40 wt.%), aluminum- (A/CNK ≥ 1.1), and alkali-rich (7.71–8.73 wt.%), with magma temperatures of 733–764 °C, which represent the highly fractionated S-type granites. They exhibit negative ε Nd (t) values (–7.49 to –6.97) and zircon ε Hf (t) values of −5.71 to +3.60, suggesting that they were generated through the anatexis of mature crustal material (pelite-dominated source). Combined with regional tectonic evolution, we propose that the Late Mesoproterozoic and Neoproterozoic granitic magmatism in the Mosuoying area is associated with continental rifting and oceanic subduction along the SW Yangtze Block, respectively. Newly obtained zircon U–Pb ages, integrated with published cassiterite U–Pb dates and field observations, indicate that the Chahe Sn deposit is spatio-temporally linked to the ca. 842–836 Ma medium- to fine-grained granites along the eastern margin of the batholith. These granites are highly fractionated with enrichment in Li, F, Rb, Cs, Ta, Sn, and W. Low Ce 4+ /Ce 3+ ratios (< 10) of magmatic zircon, together with low magnetic susceptibility (≤ 2.52 × 10 -6 emu/g) and the presence of ilmenite as the major Fe oxide in the Neoproterozoic granites, indicate that they are reduced ilmenite-series granites. Despite the similarly reduced feature, the Late Mesoproterozoic granites are commonly less fractionated and poor in Sn, lacking Sn mineralization potential. This contribution demonstrates that the Mosuoying granites were formed by distinct magmatic events rather than fractional crystallization processes, and the later episode of granitic magmatism is commonly related to economic Sn mineralization.