Selenium and tellurium systematics in MORBs from the southern Mid-Atlantic Ridge (47-50! S)
Selenium and tellurium systematics in MORBs from the southern Mid-Atlantic Ridge (47-50! S)
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DOI：
10.1016/j.gca.2014.08.023
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发表时间：
2014-11
影响因子：
5
通讯作者：
M. Lissner;S. König;A. Luguet;P. Roux;S. Schuth;A. Heuser;A. L. Roex
中科院分区：
文献类型：
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作者：
M. Lissner;S. König;A. Luguet;P. Roux;S. Schuth;A. Heuser;A. L. Roex
本文测定了20个大洋中脊玄武岩（MORB）的硒、碲含量沿着、硫和高亲铁元素（HSE）含量以及187 Os特征，这些MORB的成分从亏损的N-MORB到地幔柱相关的E-MORB不等。玻璃轮辋和结晶枕内部之间的比较表明，二次过程只反映在海水overprinted 187 Os/188 Os签名和脱气相关的低S含量的结晶枕芯，但没有影响硒和碲丰度。与此相反，在MORB分化过程中的硫化物液体的隔离降低Se和Te的浓度（分别为35%和60%），并导致更高的Se/Te比。重新计算的原始熔体Se含量对于N-和E-MORB两者广泛重叠，而原始E-MORB熔体与N-MORB熔体相比具有系统性更高的Te含量和更低的Se/Te比率（13-14 ppb Te和Se/Te = 18 vs. 9-11 ppb Te和Se/Te = 25）。如亲石微量元素和Sr-Nd-Pb同位素的限制，Se-Te系统的E-MORB地幔源的痕迹参与回收的组件可能来自附近的发现地幔柱。散装混合模型表明，除了20%的辉石熔体，或仅10 ppm的交代硫化物占的Te更丰富的E-MORB组合物。对我们的MORB数据进行硫化物分离的保守校正，结合近部分熔融模型，预测了一个Te贫化的MORB地幔储层，其非南极Se/Te为18-25，显著高于原始地幔Se/Te估计值（6.3-9.9）。这些不同的Se-Te签名之间的E-MORB地幔源，N-MORB地幔源和原始地幔的存在支持Se和Te的不相容的行为在部分熔融期间，与Te是稍微不相容。更重要的是，这强调了考虑陆地硅酸盐储层的全谱的必要性，以现实地限制这些挥发性和高度亲铁元素在散装硅酸盐地球的预算，以讨论大规模的行星过程。
Selenium and tellurium concentrations along with sulfur and Highly Siderophile Element (HSE) contents as well as187Os signatures were determined in 20 Mid-Ocean-Ridge Basalts (MORBs) from the southern Mid-Atlantic Ridge (SMAR; 47–50°S), ranging in composition from depleted N-MORBs to mantle plume-related E-MORBs. A comparison between glassy rims and crystalline pillow interiors reveal that secondary processes are only reflected in seawater-overprinted187Os/188Os signatures and degassing-related low S contents of the crystalline pillow cores but did not affect the Se and Te abundances. In contrast, the segregation of sulfide liquids during MORB differentiation lowers the Se and Te concentrations (∼35% and 60%, respectively) and leads to higher Se/Te ratios. Recomputed primitive melt Se contents broadly overlap for both, N- and E-MORBs, while primitive E-MORB melts have systematically higher Te contents and lower Se/Te ratios compared to those of the N-MORBs (13–14 ppb Te and Se/Te ≈ 18 vs. 9–11 ppb Te and Se/Te ≈ 25). As suggested by lithophile trace element and Sr–Nd–Pb isotopic constraints, the Se–Te systematics of the E-MORB mantle source traces the involvement of a recycled component likely derived from the nearby Discovery mantle plume. Bulk mixing models suggests an addition of either 20% pyroxenitic melts, or only 10 ppm of metasomatic sulfides to account for the Te-richer E-MORB compositions. A conservative correction of our MORB data for sulfide segregation combined with a near fractional melting model predicts a Te-depleted MORB mantle reservoir with a non-chondritic Se/Te of 18–25, significantly higher than the primitive mantle Se/Te estimates (6.3–9.9). The existence of these different Se–Te signatures between the E-MORB mantle source, the N-MORB mantle source and the primitive mantle support an incompatible behavior of both Se and Te during partial melting, with Te being slightly more incompatible. More importantly, this stresses the necessity of considering the full spectrum of the terrestrial silicate reservoirs to realistically constrain the budget of these volatile and highly siderophile elements in the bulk silicate Earth in order to discuss large scale planetary processes.