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<p>Eleven surface sediment samples collected from four hydrothermal fields located in the Okinawa Trough (OT) were analyzed by sequential extraction and Sr-Nd-Pb isotopic compositions. The results show that in the near-vent sediments, the weight percentage of the Fe-Mn oxide phase (FM-phase) and residual phase (R-phase) were elevated indicating the hydrothermal materials were mainly present in these two phases. In the FM-phases, the Sr isotope ranged from 0.709 17 to 0.711 981, values that were close to or slightly higher than that of OT seawater (0.709 24), supporting a predominantly seawater-derived origin. In contrast, the εNd values in near-vent sediments (−2.27–−4.36) in the middle OT (M-OT) were higher than the seawater (−3–−6), indicating the contribution by hydrothermal activity. Compared with the sediments farther from vents, the relatively lower Sr isotope (0.709 540–0.717 980) and slightly higher εNd values (−7.45–−10.24) in the R-phases in most near-vent sediments suggested that there was likely an addition of hydrothermal components. In contrast, the lower εNd values (−10.52–−11.49) and the higher Sr isotope values (0.710 313–0.719 827) in the sediments farther from vents demonstrated that the contribution of terrigenous materials was increased. In the R-phases, the Pb isotope of near-vent sediments closely resembled those of OT ores. Sediments (2-T3, 2-S7, 2-T6) collected farther from the vents exhibit Pb isotopic compositions similar to those of OT ore and M-OT lavas, indicating that hydrothermal activity had influenced sediments even at greater distances (∼3 km) from the vents. The findings indicated that the weight percentage of the FM-phase and R-phase, the Sr-Nd-Pb isotope in the R-phases, Nd isotope in the FM-phases could sensitively reflect the influence of hydrothermal activity. In addition, for sediments far from vents, the Pb isotope can also effectively trace the influence of hydrothermal activity. This study provided sensitive indicators for tracing hydrothermal activity in back-arc systems.</p>

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Hydrothermal signatures of sediments in the Okinawa Trough detected by element sequential extraction and the Sr-Nd-Pb isotopic composition

  • 期刊论文

  • 发表日期：

    2026年6月29日

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  • Shaojie Gan,
  • Baoju Yang,
  • Ying Zhang,
  • Jihua Liu

摘要

Eleven surface sediment samples collected from four hydrothermal fields located in the Okinawa Trough (OT) were analyzed by sequential extraction and Sr-Nd-Pb isotopic compositions. The results show that in the near-vent sediments, the weight percentage of the Fe-Mn oxide phase (FM-phase) and residual phase (R-phase) were elevated indicating the hydrothermal materials were mainly present in these two phases. In the FM-phases, the Sr isotope ranged from 0.709 17 to 0.711 981, values that were close to or slightly higher than that of OT seawater (0.709 24), supporting a predominantly seawater-derived origin. In contrast, the εNd values in near-vent sediments (−2.27–−4.36) in the middle OT (M-OT) were higher than the seawater (−3–−6), indicating the contribution by hydrothermal activity. Compared with the sediments farther from vents, the relatively lower Sr isotope (0.709 540–0.717 980) and slightly higher εNd values (−7.45–−10.24) in the R-phases in most near-vent sediments suggested that there was likely an addition of hydrothermal components. In contrast, the lower εNd values (−10.52–−11.49) and the higher Sr isotope values (0.710 313–0.719 827) in the sediments farther from vents demonstrated that the contribution of terrigenous materials was increased. In the R-phases, the Pb isotope of near-vent sediments closely resembled those of OT ores. Sediments (2-T3, 2-S7, 2-T6) collected farther from the vents exhibit Pb isotopic compositions similar to those of OT ore and M-OT lavas, indicating that hydrothermal activity had influenced sediments even at greater distances (∼3 km) from the vents. The findings indicated that the weight percentage of the FM-phase and R-phase, the Sr-Nd-Pb isotope in the R-phases, Nd isotope in the FM-phases could sensitively reflect the influence of hydrothermal activity. In addition, for sediments far from vents, the Pb isotope can also effectively trace the influence of hydrothermal activity. This study provided sensitive indicators for tracing hydrothermal activity in back-arc systems.