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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Global structure of mantle isotopic heterogeneity and its implications for mantle differentiation and convection
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Global structure of mantle isotopic heterogeneity and its implications for mantle differentiation and convection

机译：地幔同位素异质性的整体结构及其对地幔分化和对流的影响

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摘要

In order to further our understanding of the global geochemical structure and mantle dynamics, a global isotopic data set of oceanic basalts was analyzed by Independent Component Analysis (ICA), a relatively new method of multivariate analysis. The data set consists of 2773 mid-ocean ridge basalts (MORB) and 1515 ocean island basalts (OIB) with five isotopic ratios of Pb, Nd and Sr. The data set spatially covers the major oceans and enables us to compare the results with global geophysical observations. Three independent components (ICs) have been found, two of which are essentially identical to those previously found for basalts from the Atlantic and Indian Oceans. The two ICs (IC1 and IC2) span a compositional plane that accounts for 95.7% of the sample variance, while the third IC (IC3) accounts for 3.7%. Based on the geochemical nature of ICs and a forward model concerning trace elemental and isotopic compositions, the origin of the ICs is discussed. IC1 discriminates OIB from MORB, and may be related to elemental fractionation associated with melting and the subsequent radiogenic in growth with an average recycling time of 0.8 to 2.4. Ga. IC2 tracks the regional provenance of both MORB and OIB and may be related to aqueous fluid-rock interaction and the subsequent radiogenic ingrowth with an average recycling time of 0.3 to 0.9. Ga. IC3 fingerprints upper continental crustal material and its high value appears in limited geographical and tectonic settings. Variations in the melt component (IC1) and in the aqueous fluid component (IC2) inherited in the mantle most likely reflect mid-ocean ridge and subduction zone processes, respectively. Long-term accumulation of dense materials rich in the IC1 melt component at the base of the convective mantle accounts for its longer recycling time with respect to that for less dense materials rich in the aqueous fluid component (IC2). IC2 broadly correlates with the seismic velocity structures of the lowermost mantle and electric conductivity around the mantle transition zones. We propose that IC2 reflects hydrogen distribution within the mantle and that several global domains enriched in hydrogen could exist as vertical sectors extending all the way down to the core-mantle boundary.
机译：为了进一步了解全球地球化学结构和地幔动力学，通过独立成分分析（ICA）对海洋玄武岩的全球同位素数据集进行了分析，这是一种相对较新的多元分析方法。该数据集由2773个中洋脊玄武岩（MORB）和1515个海洋岛屿玄武岩（OIB）组成，其中Pb，Nd和Sr的同位素比为5。该数据集在空间上覆盖了主要海洋，使我们能够将结果与全球范围进行比较。地球物理观测。已经发现了三个独立的成分（IC），其中两个与以前从大西洋和印度洋的玄武岩中发现的成分基本相同。两个IC（IC1和IC2）跨越组成平面，占样本方差的95.7％，而第三个IC（IC3）占3.7％。基于离子色谱的地球化学性质和关于痕量元素和同位素组成的正向模型，讨论了离子色谱的起源。 IC1可以将MORB与OIB区别开来，并且可能与熔解相关的元素分级分离以及随后的放射生长相关，平均回收时间为0.8到2.4。 Ga。IC2跟踪MORB和OIB的区域物源，并且可能与含水流体-岩石相互作用以及随后的放射源向内生长有关，平均回收时间为0.3到0.9。 Ga。IC3指纹识别了上地壳物质，其高价值出现在有限的地理和构造环境中。地幔中遗传的熔体组分（IC1）和含水流体组分（IC2）的变化最可能分别反映了洋中脊和俯冲带的过程。与对流密度较低的材料（富含含水流体组分（IC2））相比，在对流幔底部长期富集富含IC1熔体组分的致密材料的循环时间更长。 IC2与最低地幔的地震速度结构和地幔过渡带周围的电导率大致相关。我们提出，IC2反映了地幔中的氢分布，并且可能存在一些富含氢的全球域，因为垂直扇区一直延伸到核心-地幔边界。

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