Novel insights from Fe-isotopes into the lithological heterogeneity of Ocean Island Basalts and plume-influenced MORBs
Novel insights from Fe-isotopes into the lithological heterogeneity of Ocean Island Basalts and plume-influenced MORBs
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DOI：
10.1016/j.epsl.2020.116114
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发表时间：
2020-04-01
影响因子：
5.3
通讯作者：
Williams, Helen M.
中科院分区：
文献类型：
--
作者：
Gleeson, Matthew L. M.;Gibson, Sally A.;Williams, Helen M.
在地球对流地幔的岩性不均匀性的程度是高度争论。虽然在洋岛玄武岩（OIBs）的地幔源区的辉石岩的存在传统上被限制使用的橄榄石斑晶的微量元素化学，最近的研究表明，原始橄榄石的Ni和Mn含量的地幔熔融的条件，以及岩浆房过程的影响。然而，由于地幔岩石学性质对固体地幔物质在绝热上升过程中遵循的P-T路径以及上涌地幔柱的密度的影响，限制地幔岩石学性质是重要的。因此，我们探索了使用铁同位素作为追踪全球洋中脊系统和OIB地幔柱影响段下地幔源区岩性非均质性的新方法。（δ Fe-56）和微量元素数据的26玄武玻璃从羽-影响了加拉帕戈斯扩张中心，以探讨辉石岩和橄榄岩在大洋玄武岩地幔源区的相对作用。我们的数据显示，加拉帕戈斯扩张中心玄武岩的铁同位素组成具有显著的不均匀性（+0.05至+0.25ppm），这与关键的主元素和微量元素参数（如CaO（8）/Al2O3（8），[La/Sm]（n））相关。应用新的模型来计算地幔熔融过程中的Fe同位素分馏，旁边的Monte Carlo模拟熔融的2-组分橄榄岩地幔，表明这种变化不能引起的熔融过程和/或氧逸度的橄榄岩地幔的变化。相反，我们的新的三角洲Fe-56的数据是最好的解释同位素重辉石岩衍生的熔体，有助于GSC玄武岩的比例的变化，并最终表明，岩性异质性存在于加拉帕戈斯地幔柱。我们的研究结果有一定的影响，中等重三角洲Fe-56组合物测量的羽流影响的玄武岩从社会群岛，罗尚博岭的劳弧后盆地，和著名的部分大西洋中脊，我们建议也可能代表贡献从辉石衍生的熔体。(C)2020爱思唯尔B.V.保留所有权利。
The extent of lithological heterogeneity in the Earth's convecting mantle is highly debated. Whilst the presence of pyroxenite in the mantle source regions of Ocean Island Basalts (OIBs) has traditionally been constrained using the minor-element chemistry of olivine phenocrysts, recent studies have shown that the Ni and Mn contents of primitive olivines are influenced by the conditions of mantle melting, as well as magma chamber processes. Nevertheless, constraining the lithological properties of the mantle is important due to its influenceon the P-T path followed by solid mantle material during adiabatic ascent, as well as the density of upwelling mantle plumes. We have therefore explored the use of Fe-isotopes as a novel method of tracing lithological heterogeneity in the mantle source regions beneath plume-influenced segments of the global Mid-Ocean Ridge system as well as OIBs.We present new Fe-isotope (delta Fe-56) and trace-element data for 26 basaltic glasses from the plume-influenced Galapagos Spreading Centre to investigate the relative roles of pyroxenite and peridotite in the mantle source region of oceanic basalts. Our data reveals significant heterogeneity in the Fe-isotope composition of the Galapagos Spreading Centre basalts (+0.05 to +0.25 parts per thousand delta Fe-56), which correlates with key major- and trace-element parameters (e.g. CaO(8)/Al2O3(8), [La/Sm](n)). Application of new models developed to calculate Fe-isotope fractionation during mantle melting, alongside Monte Carlo simulations for melting of a 2-component peridotite mantle, show that this variation cannot be caused by changes in melting processes and/or oxygen fugacity of a peridotitic mantle. Instead, our new delta Fe-56 data is best explained by variations in the proportion of isotopically-heavy pyroxenite-derived melt that contributes to the GSC basalts, and conclusively shows that lithological heterogeneity exists in the Galapagos mantle plume. Our findings have implications for the moderately-heavy delta Fe-56 compositions measured in plume-influenced basalts from the Society Islands, Rochambeau Ridges of the Lau back-arc basin, and the FAMOUS segment of the Mid-Atlantic Ridge, which we suggest may also represent contribution from pyroxenite-derived melts. (C) 2020 Elsevier B.V. All rights reserved.