Helium isotopes of seawater in the Philippine Sea and the western North Pacific

Takahata, Naoto; Tokukake, Taichi; Shirai, Kotaro; Fujio, Shinzou; Tanaka, Kiyoshi; Sano, Yuji

doi:10.2343/geochemj.1.0095

Cited by 7 publications

(8 citation statements)

References 19 publications

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“…The high 3 He/ 4 He ratio of 1.70 Ra at site PC9 is remarkably higher than the average value of approx. 1.15 Ra reported for northwest Pacific bottom seawater 29 , which is also verified from bottom seawater samples at sites MC3 and MC4 (Figs. 1 , 2 a, Supplementary Table S1 ).…”

Section: Resultssupporting

confidence: 82%

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Mantle-derived helium released through the Japan trench bend-faults

Park

Takahata

Hondori

et al. 2021

Sci Rep

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Plate bending-related normal faults (i.e. bend-faults) develop at the outer trench-slope of the oceanic plate incoming into the subduction zone. Numerous geophysical studies and numerical simulations suggest that bend-faults play a key role by providing pathways for seawater to flow into the oceanic crust and the upper mantle, thereby promoting hydration of the oceanic plate. However, deep penetration of seawater along bend-faults remains controversial because fluids that have percolated down into the mantle are difficult to detect. This report presents anomalously high helium isotope (3He/4He) ratios in sediment pore water and seismic reflection data which suggest fluid infiltration into the upper mantle and subsequent outflow through bend-faults across the outer slope of the Japan trench. The 3He/4He and 4He/20Ne ratios at sites near-trench bend-faults, which are close to the isotopic ratios of bottom seawater, are almost constant with depth, supporting local seawater inflow. Our findings provide the first reported evidence for a potentially large-scale active hydrothermal circulation system through bend-faults across the Moho (crust-mantle boundary) in and out of the oceanic lithospheric mantle.

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Section: Resultssupporting

confidence: 82%

“…Vertical gray zone marks the 3 He/ 4 He ratio of ca. 1.15 Ra, which represents average northwest Pacific bottom seawater 29 . The helium isotopes ratios at site PC9 increase with depth, whereas those at site PC8 are almost constant at ca.…”

Section: Resultsmentioning

confidence: 99%

Mantle-derived helium released through the Japan trench bend-faults

Park

Takahata

Hondori

et al. 2021

Sci Rep

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“…9). The northwest Pacific bottom seawater consistently shows elevated 3 He compared with atmospheric values: excess 3 He values of 18% at 2,000 m ( Supplementary Figs 1 and 2) result from abyssal currents dispersing mantle 3 He released from mid-oceanic-ridge volcanism 10 , which explains why the 3 He/ 4 He ratios decrease with increasing depth at sites N1 and N2 (grey shades in Fig. 2c,d).…”

Section: Resultsmentioning

confidence: 77%

“…Therefore, the excess 3 He is derived from long distance transportation by the abyssal current at B10,000 km (ref. 10). This movement may homogenize the 3 He/ 4 He signatures at the same depth for several hundred kilometres in a horizontal direction, which would assure the robustness of the normal 3 He profile in the trench region before the earthquake.…”

Section: Methodsmentioning

confidence: 99%

Helium anomalies suggest a fluid pathway from mantle to trench during the 2011 Tohoku-Oki earthquake

et al. 2014

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Geophysical evidence suggests that fluids along fault planes have an important role in generating earthquakes; however, the nature of these fluids has not been well defined. The 2011 magnitude 9.0 Tohoku-Oki earthquake ruptured the interface between the subducting Pacific plate and the overlying Okhotsk plate. Here we report a sharp increase in mantlederived helium in bottom seawater near the rupture zone 1 month after the earthquake. The timing and location indicate that fluids were released from the mantle on the seafloor along the plate interface. The movement of the fluids was rapid, with a velocity of B4 km per day and an uncertainty factor of four. This rate is much faster than what would be expected from pressure-gradient propagation, suggesting that over-pressurized fluid is discharged along the plate interface.

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“…The 3 He/ 4 He ratios of the SCS crust HYD66-1 is 1.08 R A and the 3 He concentrations of the SCS sample HYD66-1, ST1 and STD275 range from 9.64 × 10 −14 to 10.91 × 10 −14 (cm 3 ·STP·g −1 ), which are distinctly higher than those of the radiogenic crust and air-saturated seawater. The isotopic ratio of helium dissolved in seawater gradually increase with water depth in the Pacific and adjacent seas of Southwest Japan, which contains excess 3 He in the deep water derived from the mantle source [5,8,76,77,[80][81][82][83]. This reflects that the excess 3 He in the SCS sample HYD66-1, ST1 and STD275 may have trapped the He released into seawater by the mantle degassing from the underlying seamounts and/or seawater-rock alteration of submarine basalt.…”

Section: Mantle Sourcementioning

confidence: 99%

Helium and Argon Isotopes in the Fe-Mn Polymetallic Crusts and Nodules from the South China Sea: Constraints on Their Genetic Sources and Origins

et al. 2018

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In this study, the He and Ar isotope compositions were measured for the Fe-Mn polymetallic crusts and nodules from the South China Sea (SCS), using the high temperature bulk melting method and noble gases isotope mass spectrometry. The He and Ar of the SCS crusts/nodules exist mainly in the Fe-Mn mineral crystal lattice and terrigenous clastic mineral particles. The results show that the 3 He concentrations and R/R A values of the SCS crusts are generally higher than those of the SCS nodules, while 4 He and 40 Ar concentrations of the SCS crusts are lower than those of the SCS nodules. Comparison with the Pacific crusts and nodules, the SCS Fe-Mn crusts/nodules have lower 3 He concentrations and 3 He/ 4 He ratios (R/R A , 0.19 to 1.08) than those of the Pacific Fe-Mn crusts/nodules, while the 40 Ar/ 36 Ar ratios of the SCS samples are significantly higher than those of the Pacific counterparts. The relatively low 3 He/ 4 He ratios and high 40 Ar concentrations in the SCS samples are likely caused by terrigenous detrital input with high radiogenic 4 He and 40 Ar contents. The SCS crusts and nodules have shorter growth periods, implying that in situ post-formation radiogenic 3 He, 4 He and 40 Ar produced by decay of U, Th and K have no effect on their isotope compositions. Thus, the SCS crusts/nodules inherited the noble gases characteristics of their sources. Helium and Ar isotope compositions in the SCS Fe-Mn crusts and nodules reflect the product of an equilibrium mixture between air-saturated seawater and radiogenic components during their growth, while the partial 3 He excess in some SCS samples may represent a little mantle-derived origin. The different He and Ar isotope compositions of the Fe-Mn crusts and nodules between the South China Sea and the Pacific Ocean are due to their different sources and genetic processes. The characteristics of He and Ar isotope compositions in the SCS polymetallic crusts and nodules are similar to the properties of hydrogenetic Fe-Mn oxide/hydroxide precipitates, which reflects mainly the product of an equilibrium mixture between air-saturated seawater and radiogenic components.isotopes provide important geological information for the research of modern ocean circulation, paleoceanography, seafloor hydrothermal and cold brine system and ocean/atmosphere gas exchange.Early studies of marine noble gases are mainly concentrated in solving geochemical problems, such as tracing the excess He in the seawater, which is likely produced by U-Th series radioactive decay in the marine sediments [1,2]. After the discovery of mantle-originated helium [3] and 3 He originated near the sediment surface (via 3 H decay in the sea) [4], people began to use noble gases to trace the source of submarine hydrothermal fluids, crust/mantle material cycle, constrain the formation process and thermodynamic mechanism of seamount systems [5][6][7][8][9][10][11] and to explore the formation and cycle of the ocean currents (e.g., [12][13][14]).Some studies have explored potential application of He isotopes...

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Helium isotopes of seawater in the Philippine Sea and the western North Pacific

Cited by 7 publications

References 19 publications

Mantle-derived helium released through the Japan trench bend-faults

Mantle-derived helium released through the Japan trench bend-faults

Helium anomalies suggest a fluid pathway from mantle to trench during the 2011 Tohoku-Oki earthquake

Helium and Argon Isotopes in the Fe-Mn Polymetallic Crusts and Nodules from the South China Sea: Constraints on Their Genetic Sources and Origins

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