Noble gas systematics in new popping rocks from the Mid-Atlantic Ridge (14°N): Evidence for small-scale upper mantle heterogeneities
Noble gas systematics in new popping rocks from the Mid-Atlantic Ridge (14°N): Evidence for small-scale upper mantle heterogeneities
复制标题
大西洋中脊（北纬 14°）新爆裂岩石中的稀有气体系统学：小规模上地幔异质性的证据
DOI：
10.1016/j.epsl.2019.04.037
复制
发表时间：
2019
影响因子：
5.3
通讯作者：
E. Mittelstaedt
中科院分区：
文献类型：
--
作者：
S. Péron;M. Moreira;M. Kurz;J. Curtice;J. Blusztajn;B. Putlitz;V. Wanless;Meghan R. Jones;S. Soule;E. Mittelstaedt
地球挥发分的起源和演化是地球和行星科学中的一个基本问题。为了更好地解决这一问题，有必要估计地幔中挥发物的同位素和元素组成，这是困难的，因为岩浆运输到地表时的脱气改变了最初的元素组成。然而，一些玄武岩被认为是相对未脱气的，因此可以用来确定地幔中C，N，H2O和稀有气体的浓度。1985年在大西洋中脊14°N附近发现的所谓爆裂岩样品2πD43就是这种情况，由于其高气体含量，它被认为是上地幔同位素和元素挥发物组成的参考。这种富含气体的样品只在大洋中脊的少数地方被发现，但对于确定地幔成分的不均匀性以及地球上挥发物的循环至关重要。为了更好地了解地球上爆裂岩的发生、地幔不均匀性和挥发分循环，于2016年在14°N附近的大西洋中脊进行了AT 33 -03考察。在与样品2πD43相同的区域发现了爆裂岩石，使用可浸没的Alvin，并通过阶梯破碎和激光烧蚀确定了它们的惰性气体成分。一个新的厌氧采样协议进行了测试，试图尽量减少大气污染，这是普遍存在的玄武岩玻璃样品用于惰性气体分析，并评估激光提取技术。初步的分步破碎结果表明，新的厌氧采样协议减少了大气对惰性气体测量的影响。与激光烧蚀数据的比较表明，仍然存在一些大气污染，这表明污染始于海底。根据稀有气体成分，鉴定出两组样品：一组样品的最高测量比率与2πD43样品相似（20 Ne/22 Ne为12.5，40 Ar/36 Ar为127，000），另一组样品的最高稀有气体比率较低（20 Ne/22 Ne为12.2，40 Ar/36 Ar为16，100），氩浓度较高。根据这些结果，结合Cl/K和H2O/Ce比值以及铅、锶、钕同位素初步数据，沿着认为这两组样品反映了不同地幔源区的独立喷发事件。这为上地幔在小尺度上的不均匀性提供了证据，并可能意味着具有较低的氖和氩同位素比值的地幔源更多地受到大气惰性气体再循环的影响。
The origin and evolution of terrestrial volatiles is a fundamental question in Earth and planetary sciences. To better address this, it is necessary to estimate the present-day isotopic and elemental composition of volatiles in the mantle, which is difficult because degassing during magma transport to the surface changes the initial elemental composition. However, some basalts are considered to be relatively un-degassed and therefore can be used to determine the concentrations of C, N, H2O and noble gases in the mantle. This is the case of the so-called popping rock sample 2πD43, found near 14°N on the Mid-Atlantic Ridge in 1985, which has been considered as a reference for upper mantle isotopic and elemental volatile compositions due to its high gas content. Such gas-rich samples have been recovered in only a few places on mid-ocean ridges but are crucial to characterizing the heterogeneities in mantle composition and therefore the cycling of volatiles on Earth. In order to better understand the occurrence of popping rocks, mantle heterogeneities and volatile cycling on Earth, cruise AT33-03 onR/V Atlantiswas conducted in 2016 on the Mid-Atlantic Ridge near 14°N. Popping rocks were found in the same area as sample 2πD43, using the submersibleAlvin, and their noble gas compositions were determined by step-crushing and laser ablation. A new anaerobic sampling protocol was tested in an attempt to minimize atmospheric contamination, which is ubiquitous in basaltic glass samples used for noble gas analyses, and to evaluate laser extraction techniques. Preliminary step-crushing results suggest that the new anaerobic sampling protocol reduces atmospheric influence on the noble gas measurements. Comparison with laser ablation data shows that there is still some atmospheric contamination, suggesting that contamination begins on the seafloor. Two groups of samples have been identified based on their noble gas compositions: one group with their highest measured ratios similar to those of sample 2πD43 (20Ne/22Ne of ∼12.5,40Ar/36Ar of ∼27,000), and another group with lower maximum noble gas ratios (20Ne/22Ne of 12.2,40Ar/36Ar of 16,100) and higher argon concentrations. Based on these results, along with Cl/K and H2O/Ce ratios and preliminary lead, strontium and neodymium isotope data, it is suggested that these two groups of samples reflect separate eruptive events that originated from distinct mantle sources. This provides evidence for upper mantle heterogeneity at small scales and could imply that the mantle source with lower neon and argon isotopic ratios has been more influenced by recycling of atmospheric noble gases.
DOI：
10.1002/ggge.20046
发表时间：
2013
期刊：
Geochemistry, Geophysics, Geosystems
影响因子：
--
作者：
Wilson S
通讯作者：
Wilson S
大西洋中脊爆裂岩石对地幔碳的新限制
影响因子：
5.3
作者：
Jones, M.R.;Wanless, V.D.;Soule, S.A.;Kurz, M.D.;Mittelstaedt, E.;Fornari, D.J.;Curtice, J.;Klein, F.;Le Roux, V.;Brodsky, H.
通讯作者：
Brodsky, H.