Mantle degassing of primordial helium through submarine ridge flank basaltic basement
Mantle degassing of primordial helium through submarine ridge flank basaltic basement
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原始氦通过海底脊侧玄武岩基底的地幔脱气
DOI：
10.1016/j.epsl.2020.116386
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发表时间：
2020
影响因子：
5.3
通讯作者：
Rappé, Michael S.
中科院分区：
文献类型：
--
作者：
Lin, Huei-Ting;Lilley, Marvin D.;Lupton, John E.;Rappé, Michael S.
海底热液柱、喷口流体和来自大洋中脊(MOR)活动热液系统和俯冲带火山作用的地幔岩样中的高He 3/4He比值证明了地球内部原始气体的脱气作用。作为地球上最大的含水层，最上层40-500m的可渗透海底脊侧基底(1-6500万年，Myr)容纳了∼2%的海洋体积，占海底热流的70%。然而，原始气体通过大洋脊侧地壳的脱气作用尚未被直接量化。在这里，我们证明了来自胡安德富卡山脊(JdFR)东侧埋藏的3.5Myr玄武岩地壳的高完整性热液(65℃)流体含有升高的3He。玄武岩流体的He3/4He为4.5±0.1Ra(相对于空气系数)，与深海水(1.05Ra)相比有很大提高，但仅为MOR释放的高温喷口流体(∼8Ra)的一半。在脊侧流体中，只有一小部分3He来自高温脊轴流体的夹带，更好地解释了地幔通过地幔-地壳边界的脱气作用。低于MORHe的3/4He比值表明，放射性成因的4He来自地幔内古老的铀和钍的衰变以及山脊两侧的玄武岩。通过温暖的海脊侧翼(4.9-36摩尔/年)放出的3He占全球3He放气的0.7-6%，只有通过大洋中脊和俯冲火山作用才能超过。地幔3的存在表明，脊侧流体中存在的非生物甲烷可能来自地幔。根据~3He放气通量，估算出海脊两侧可能存在的地幔来源的非生物甲烷产生率为0.3-35×108mol/a。
The degassing of primordial gases from Earth's interior is evidenced by the high He 3/4 He ratios in submarine hydrothermal plumes, vent fluids, and rock samples with mantle origin from active hydrothermal systems in mid-ocean ridges (MOR) and subduction zone volcanism. As the largest aquifer on Earth, the uppermost 40-500 m of permeable submarine ridge flank basement (1-65 million-years-old, Myr) holds∼ 2% of the ocean volume and accounts for 70% of the seafloor hydrothermal heat flux. However, the degassing of primordial gases through the oceanic ridge flank crust has not yet been directly quantified. Here, we show that high integrity hydrothermal (65° C) fluids from the sediment-buried 3.5 Myr basaltic crust from the eastern flank of the Juan de Fuca Ridge (JdFR) contain elevated 3 He. The He 3/4 He for the basaltic fluid is 4.5±0.1 R a (relative to the air ratio), which is greatly elevated when compared to deep seawater (1.05 R a), but is half of that observed for high-temperature vent fluids (∼ 8 R a) emitting from MOR. Only a small fraction of the 3 He in ridge flank fluids is derived from the entrainment of high-temperature ridge-axis fluids and is better explained by degassing of the mantle through the mantle-crust boundary. The lower than MOR He 3/4 He ratios indicate that radiogenic 4 He originates from aged uranium and thorium decay within the mantle as well as from the ridge-flank basalts. The 3 He outgassing through warm ridge flanks (4.9 to 36 mol/yr) accounts for 0.7-6% of the global 3 He outgassing, exceeded only by degassing through mid-ocean ridges and subduction volcanism. The presence of mantle 3 He suggests that the abiogenic methane present in the ridge flank fluids might be mantle-derived. Based on the 3 He outgassing flux, a possibly mantle-derived abiotic methane production rate at the ridge flank is estimated to be 0.3–35× 10 8 mol/yr.
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发表时间：
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作者：
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J. Erzinger
DOI：
10.1098/rsta.2018.0431
发表时间：
2020-02-21
影响因子：
5
作者：
Grozeva, Niya G.;Klein, Frieder;Sylva, Sean P.
通讯作者：
Sylva, Sean P.
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DOI：
--
发表时间：
1992
期刊：
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作者：
T. Torgersen;W. B. Clarke
通讯作者：
W. B. Clarke
影响因子：
64.8
作者：
JENKINS, WJ;EDMOND, JM;CORLISS, JB
通讯作者：
CORLISS, JB