Negligible sulfur isotope fractionation during partial melting: Evidence from Garrett transform fault basalts, implications for the late-veneer and the hadean matte
Negligible sulfur isotope fractionation during partial melting: Evidence from Garrett transform fault basalts, implications for the late-veneer and the hadean matte
复制标题
部分熔融过程中可忽略不计的硫同位素分馏：来自加勒特变换断层玄武岩的证据，对晚单板和玄武岩的影响
DOI：
10.1016/j.epsl.2016.07.012
复制
发表时间：
2016
影响因子：
5.3
通讯作者：
P. Cartigny
中科院分区：
文献类型：
--
作者：
Jabrane Labidi;P. Cartigny
本文报道了采自加勒特转换断层的11个玄武岩的四重硫同位素组成、硫含量、主微量元素（包括铜和氯的丰度）形态。我们联合收割机这些数据来讨论的情况下，S同位素分馏沿着部分熔融和低压分离结晶。K2 O/TiO 2和La/SmN比值的变化（分别在0.017 ~ 0.067和0.31 ~ 0.59之间）表明，加勒特熔岩中存在一定的亏损，包括超亏损样品（K2 O/TiO 2< 0.03）。不相容元素贫化的显著水平与贫化源的重熔一致。与不相容元素贫化相比，所有样品显示类似的S和Cu丰度（在给定的主元素组成）洋中脊玄武岩（MORB）。这表明，加勒特帧内变换熔岩（ITL）是硫化物饱和的MORB。加勒特母体熔体（MgO> 8%）的铜含量为1080 ppm，与MORB不可区分。这就需要它们的地幔源，不相容元素的耗尽，宿主残留的硫化物缓冲所有爆发熔体的铜含量。我们计算出超贫化加勒特熔岩源的最低硫含量为100±40 ppm S，即大约是MORB地幔源的2倍。排除Cl/K比> 0.1的可能经历了热液硫化物同化的单个样品后，加勒特ITL显示出均匀的δ 34 S、Δ 33 S和Δ 36 S值，平均值分别为− 0.68±0.08‰、+ 0.010±0.005‰和− 0.04±0.04‰（均为1σ，n= 10）。δ 34 S值与K2 O/TiO 2变化及硫化物分馏程度无关。从这些观测结果中，我们得出了出溶硫化物和溶解在硅酸盐熔体中的硫化物之间的34 S/32 S分馏因子为1.0000±0.0003。部分熔融过程中的S同位素分馏可以忽略不计，MORB和ITLs都记录了地幔源区的34 S/32 S比值。在行星分化过程中，硫化物熔体从地幔中分离出来，下沉并被添加到核心的概念被称为“Hadean Matte”。行星分异过程中地幔中硫化物向地核的分凝作用可以解释地幔的各种地球化学特征。根据硫同位素质量平衡，我们得出了一个下限和上限的Hadean冰铜。虽然下限对应于几乎可以忽略不计的冥古宙冰铜，但上限为3.36× 1024 g S（即陆地S总量的约10%），仍然比以前的估计低5到10倍。尽管如此，这一上限要求在提取深成锍之前地幔硫含量高于1000 ppm。这一建议将有时间上的要求，要求任何硫化物熔体形成后，核心提取，但在晚期增生的高度亲铁元素。
We report the quadruple sulfur isotope compositions, sulfur contents and speciation major and trace elements (including copper and chlorine abundances) of eleven basalts collected in the Garrett transform fault. We combine these data to discuss the absence of S isotopic fractionation along both partial melting and low-pressure fractional crystallization. The variations of K 2 O/TiO 2 and La/Sm N-ratios (respectively between 0.017 and 0.067, and between 0.31 and 0.59) suggest a range of depletion in Garrett lavas that includes ultra depleted samples (K 2 O/TiO 2< 0.03). The remarkable level of incompatible element depletion is consistent with re-melting of a depleted source. Contrasting with incompatible element depletion, all samples display similar S and Cu abundance (at a given major-element composition) to mid-ocean ridge basalts (MORB). This indicates that Garrett Intra Transform Lavas (ITL) are sulfide saturated as MORB are. Copper content for Garrett parental melts (MgO> 8%) are∼ 80 ppm, indistinguishable from MORBs. This requires their mantle sources, variably depleted in incompatible element, to host residual sulfide buffering the Cu content of all erupted melts. We calculate a minimum S content for the source of ultra-depleted Garrett lavas of 100±40 ppm S, ie roughly a factor of 2 below the MORB mantle source. After exclusion of a single sample with Cl/K ratio> 0.1 that likely experienced hydrothermal sulfide assimilation, Garrett ITLs display homogeneous δ 34 S, Δ 33 S and Δ 36 S values with averages of− 0.68±0.08‰,+ 0.010±0.005‰ and− 0.04±0.04‰, respectively (all 1σ, n= 10). The δ 34 S values display no relationship with either K 2 O/TiO 2 variations or extent sulfide fractionation. From these observations, we derive a 34 S/32 S fractionation factor between exsolved sulfides and sulfide dissolved in silicate melts of 1.0000±0.0003. The S isotopic fractionation during partial melting can thus be considered as negligible, and both MORBs and ITLs record the 34 S/32 S ratio of their mantle source. The concept of sulfide melts segregating from the mantle, sinking and being added to the core during planetary differentiation was termed the ‘Hadean Matte’. The segregation of sulfides from the mantle to the core during planetary differentiation could account for various geochemical features of the Earth's mantle. Based on S isotopic mass balance, we derive a lower and upper limit for the hadean matte. While the lower bound corresponds to a virtually negligible hadean matte, the upper limit is 3.36× 10 24 g S (ie∼ 10% of the bulk terrestrial S), which remains 5 to 10 times lower than previous estimates. This upper bound nonetheless requires high mantle S content> 1000 ppm S before the extraction of the hadean matte. This suggestion would have chronological requirements, requiring any sulfide melt to have formed after the core extraction but before late accretion of the highly siderophile elements.
影响因子：
64.8
作者：
Markus Lagos;Chris Ballhaus;Carsten Münker;Cora C. Wohlgemuth-Ueberwasser;Jasper Berndt;D. V. Kuzmin
通讯作者：
Markus Lagos;Chris Ballhaus;Carsten Münker;Cora C. Wohlgemuth-Ueberwasser;Jasper Berndt;D. V. Kuzmin