Paleoarchean sulfur cycling: Multiple sulfur isotope constraints from the Barberton Greenstone Belt, South Africa
Paleoarchean sulfur cycling: Multiple sulfur isotope constraints from the Barberton Greenstone Belt, South Africa
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DOI：
10.1016/j.precamres.2015.06.008
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发表时间：
2015-09
影响因子：
3.8
通讯作者：
A. Montinaro;H. Strauss;P. Mason;D. Roerdink;C. Münker;U. Schwarz-Schampera;N. Arndt;J. Farquhar;N. Beukes;J. Gutzmer;M. Peters
中科院分区：
文献类型：
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作者：
A. Montinaro;H. Strauss;P. Mason;D. Roerdink;C. Münker;U. Schwarz-Schampera;N. Arndt;J. Farquhar;N. Beukes;J. Gutzmer;M. Peters
在南非Barberton绿岩带(3550-3215 Ma)火山岩和沉积岩中发现的依赖于质量和与质量无关的硫同位素分馏为地球早期的硫循环提供了限制。研究了四个不同的样品组：科马提岩和拉斑玄武岩、重晶石、块状和浸染型硫化物矿石以及非矿化黑色页岩。δ34S值在−0.7%和+5.2‰之间变化不大，但总体上略有正值，Δ33S值在−0.50%和−0.09‰之间为负，δ34S和Δ33S之间以及Δ33S和Δ36S之间负相关，科马提组和韦尔特夫登组的科马提岩和拉斑玄武岩和韦尔特夫登组的Komatiite和拉斑玄武岩和Weltevreden组的Komatiite和拉斑玄武岩的Δ33S和Δ36S之间的负相关超出了预期的未分级年轻硫的预期范围。相反，结果表明，大洋地壳岩石硫通过与最有可能来自海洋的流体的相互作用而发生改变。马佩组重晶石的δ34S值在+3.1‰到+8.1‰之间为正，−33S值在−0.77到‰0.34之间为负。与质量无关的硫同位素分馏指示大气硫源，特别是光解硫酸盐，而正的δ34S值表明海相硫酸盐储层的细菌硫酸盐还原。来自推定的地层相当于MAPEPE组的未矿化黑色页岩样品的正δ34S值在0.0-+1.3‰之间，正Δ33S值在+0.59-+2.45‰之间。这些结果被解释为光解元素硫的还原，带有正的Δ33S信号。正的δ34S值在+0.70到+3.5‰之间，Δ33S值在−0.17到−0.12之间的轻微负的Δ33S值表征了来自双场地展望的大量和分散的硫化物。结果表明，未分馏的年轻岩浆硫源是主要的硫源，但不能排除循环海水硫酸盐的贡献，这将指示海底的热液活动。M‘hlati远景的大量和浸染性硫化物与Bien场所远景的块状和浸染性硫化物明显不同。它们的δ34S值在−1.2~−0.1‰之间为负，Δ33S值在+2.6 6~+3.17‰之间为正，从而显示出相当大的非质量依赖性硫同位素分馏。同样，这些样本清楚地显示了大气MIF-S信号的并入。这些样品的硫源具有正的Δ33S值，表明与光解元素硫有关。综上所述，巴伯顿绿岩带古太古代岩石的硫同位素特征多种多样，表明硫的来源不同。对于Komatiite和拉斑玄武岩、重晶石和来自Bien场所的块状和可能也浸染的硫化物，多个硫同位素与周围海水硫酸盐及其光解成因有关，而来自M‘hlati和非矿化黑色页岩的块状和浸染状硫化物与第二端元(光解元素硫)有关。
Mass-dependent and mass-independent sulfur isotope fractionation archived in volcanic and sedimentary rocks from the Barberton Greenstone Belt (3550–3215 Ma), South Africa, provide constraints for sulfur cycling on the early Earth. Four different sample suites were studied: komatiites and tholeiites, barite, massive and disseminated sulfide ores, and non-mineralized black shales.Variable but generally slightly positiveδ34S values between −0.7 and +5.2‰, negativeΔ33S values between −0.50 and −0.09‰, and a negative correlation betweenδ34S andΔ33S as well as betweenΔ33S andΔ36S for komatiites and tholeiites from the Komati Formation and from the Weltevreden Formation are outside the expected range of unfractionated juvenile sulfur. Instead, results suggest alteration of oceanic crustal rock sulfur through interactions with fluids that most likely derived their sulfur from seawater.Barite from the Mapepe Formation displays positiveδ34S values between +3.1 and +8.1‰ and negativeΔ33S values between −0.77 and −0.34‰. The mass-independent sulfur isotope fractionation indicates an atmospheric sulfur source, notably photolytic sulfate, whereas the positiveδ34S values suggest bacterial sulfate reduction of the marine sulfate reservoir.Non-mineralized black shale samples from the presumed stratigraphic equivalent of the Mapepe Formation show positiveδ34S values between 0.0 and +1.3‰ and positiveΔ33S values between +0.59 and +2.45‰. These results are interpreted to result from the reduction of photolytic elemental sulfur, carrying a positiveΔ33S signature.Positiveδ34S values ranging from +0.7 to +3.5‰ and slightly negativeΔ33S values between −0.17 and −0.12‰ characterize massive and disseminated sulfides from the Bien Venue Prospect. Results suggest unfractionated juvenile magmatic sulfur source as the primary sulfur source, but a contribution from recycled seawater sulfate, which would be indicative of submarine hydrothermal activity, cannot be ruled out.Massive and disseminated sulfides from the M’hlati prospect are distinctly different from massive and disseminated sulfide from the Bien Venue Prospect. They show negativeδ34S values between −1.2 and −0.1‰ and positiveΔ33S values between +2.66 and +3.17‰, thus, displaying a sizeable mass-independent sulfur isotopic fractionation. Again, these samples clearly exhibit the incorporation of an atmospheric MIF-S signal. The source of sulfur for these samples has positiveΔ33S values, suggesting a connection with photolytic elemental sulfur.In conclusion, the sulfur isotope signatures in Paleoarchean rocks from the Barberton Greenstone Belt are diverse and indicate the incorporation of different sources of sulfur. For komatiites and tholeiites, barite and massive and possibly also disseminated sulfides from Bien Venue, multiple sulfur isotopes are related to ambient seawater sulfate and its photolytic origin, while massive and disseminated sulfides from M’hlati and non-mineralized black shales are related to a second (photolytic elemental sulfur) end member.