摘要：AbstractThis study examines the Ga isotopic compositions of sulfides in the Yuhuang and Duanqiao hydrothermal fields on the Southwest Indian Ridge, mid-ocean ridge basalts (MORB), and calcareous sediments around the hydrothermal fields. Theδ71/69GaNIST-994values of the MORB samples vary little (+1.20‰ to +1.23‰, with an average of +1.22‰) and are consistent with theδ71/69GaNIST-994values of two standard basalt samples (BCR-2 and BHVO-2), indicating that Ga isotopes may either not fractionate or fractionate only slightly under high-temperature geological processes; therefore, theδ71/69GaNIST-994value of oceanic crust may be +1.22‰. The sediments (+1.28‰ to +1.47‰, with an average of +1.38‰) are rich in heavier Ga isotopes than the basalts, and the Ga present in the sediments may have originated from soluble Ga present in the seawater that was adsorbed by (Mn, Fe) oxides/hydroxides. The Ga contribution of basaltic debris to the sediments was almost negligible. Thus, we speculate that theδ71/69GaNIST-994value of seawater in the study area fell within a range from +1.92‰ to +2.36‰. Theδ71/69GaNIST-994values of the sulfides in the Yuhuang hydrothermal field range from +0.99‰ to +1.57‰, with an average of +1.25‰, and theδ71/69GaNIST-994values of the sulfides in the Duanqiao hydrothermal field range from +0.93‰ to +1.55‰, with an average of +1.19‰. Theδ71/69GaNIST-994ranges of the sulfides in the Yuhuang and Duanqiao hydrothermal fields are similar, with the Ga isotopic fractionation reaching 0.58‰ and 0.62‰, respectively. The averageδ71/69GaNIST-994values in the sulfides are close to those in the MORBs. This suggests that Ga within the sulfides in the Yuhuang and Duanqiao hydrothermal fields mainly originated from MORBs, with seawater and sediments making only small contributions. The Ga isotopic fractionation in the sulfides may be related to processes associated with the formation of sulfides, such as rapid precipitation or the admixture of different stages of sulfide. This study is of great significance for understanding the global distribution of Ga isotopes and the Ga cycle in submarine hydrothermal systems.Graphical abstractDisplay OmittedHighlights•δ71Ga of sulfides, MORBs and sediments from the Southwest Indian Ridge are obtained.•Ga isotopic compositions of the basalts are homogeneous (+1.20‰ to +1.23‰).•δ71Ga ranges of the sulfides in the Yuhuang and Duanqiao hydrothermal fields are similar.•Ga in the sulfides from both hydrothermal fields is mainly from MORBs.•Ga in the sediments is mainly from seawater by adsorption of Fe oxides/hydroxides.
关键词：KeywordsGa isotopeHydrothermal sulfideYuhuangDuanqiaoSouthwest Indian Ridge
