Hydrogen isotopes in high 3He/4He submarine basalts: Primordial vs. recycled water and the veil of mantle enrichment
Hydrogen isotopes in high 3He/4He submarine basalts: Primordial vs. recycled water and the veil of mantle enrichment
复制标题
DOI：
10.1016/j.epsl.2018.12.012
复制
发表时间：
2019-02-15
影响因子：
5.3
通讯作者：
Garcia, Michael O.
中科院分区：
文献类型：
--
作者：
Loewen, Matthew W.;Graham, David W.;Garcia, Michael O.
地幔水的氢同位素值（Δ D）被地球历史上地表水的早期脱气和再循环所掩盖。高He-3/He-4比值在一些洋岛玄武岩，但是，提供了一个明确的地球化学签名的深，原始地幔已被隔离在地球内部的熔融，脱气，对流混合与上地幔。对阿姆斯特丹-圣保罗（ASP）高原东南印度洋海岭（SEIR）高He-3/He-4海底玄武岩玻璃进行了氢同位素测量（δ D = -51至90千分之一，He-3/He-4 = 7.6至14.1 R-A）和夏威夷岛南部Loihi海山的海底玻璃中（Δ D = -70至-90份/千，He-3/He-4 = 22.5至27.8 R-A）。这些结果突出了高He-3/He-4熔岩的Δ D的两种对比模式：一种趋势是Δ D约为千分之50，另一种趋势是Δ D =千分之-75。这些相同的模式是显而易见的，在全球汇编以前报告的delta D和He-3/He-4的结果。我们认为，高三角洲D值的结果，在俯冲过程中，被带到源区的地幔柱在核幔边界，它是混合原始地幔，导致高三角洲D和适度高的He-3/He-4的水再循环。相反，在Loihi海山玄武岩和微量元素贫化的洋中脊玄武岩中，δ D值较低，为千分之-75，这意味着原始地球氢同位素值为千分之-75或更低。δ D值下降到千分之100也出现在微量元素贫化最严重的洋中脊玄武岩中，通常与Sr-87/Sr-86比值接近0.703有关。这些较低的Δ D值可能是上地幔多阶段熔融历史的结果，其中较小的D/H分馏可能与名义上无水残留矿物中的氢保留有关。总的来说，在大多数洋中脊玄武岩和高He-3/He-4 Loihi玄武岩中，三角洲D占主导地位，约为千分之75，这与地球上的水起源是一致的，主要是由南极物质的吸积。由爱思唯尔公司出版
The hydrogen isotope value (delta D) of water indigenous to the mantle is masked by the early degassing and recycling of surface water through Earth's history. High He-3/He-4 ratios in some ocean island basalts, however, provide a clear geochemical signature of deep, primordial mantle that has been isolated within the Earth's interior from melting, degassing, and convective mixing with the upper mantle. Hydrogen isotopes were measured in high He-3/He-4 submarine basalt glasses from the Southeast Indian Ridge (SEIR) at the Amsterdam-St. Paul (ASP) Plateau (delta D = -51 to -90 parts per thousand, He-3/He-4 = 7.6 to 14.1 R-A) and in submarine glasses from Loihi seamount south of the island of Hawaii (delta D = -70 to -90 parts per thousand, He-3/He-4 = 22.5 to 27.8 R-A). These results highlight two contrasting patterns of delta D for high He-3/He-4 lavas: one trend toward high delta D of approximately 50 parts per thousand, and another converging at delta D = -75 parts per thousand. These same patterns are evident in a global compilation of previously reported delta D and He-3/He-4 results. We suggest that the high delta D values result from water recycled during subduction that is carried into the source region of mantle plumes at the core-mantle boundary where it is mixed with primordial mantle, resulting in high delta D and moderately high He-3/He-4. Conversely, lower delta D values of -75 parts per thousand, in basalts from Loihi seamount and also trace element depleted mid-ocean ridge basalts, imply a primordial Earth hydrogen isotopic value of -75 parts per thousand or lower. delta D values down to 100 parts per thousand also occur in the most trace element depleted mid-ocean ridge basalts, typically in association with Sr-87/Sr-86 ratios near 0.703. These lower delta D values may be a result of multi-stage melting history of the upper mantle where minor D/H fractionation could be associated with hydrogen retention in nominally anhydrous residual minerals. Collectively, the predominance of delta D around 75 parts per thousand in the majority of mid-ocean ridge basalts and in high He-3/He-4 Loihi basalts is consistent with an origin of water on Earth that was dominated by accretion of chondritic material. Published by Elsevier B.V.