Earth and Planetary Science Letters ( IF 5.3 ) Pub Date : 2021-08-09 , DOI: 10.1016/j.epsl.2021.117118 Sara Burness 1, 2 , Emilie Thomassot 3 , Katie A. Smart 1 , Sebastian Tappe 2, 4
Multiple sulphur isotopic compositions of sulphides from Kaapvaal craton mantle eclogites allow to elucidate the recycling of sulphur into the deep Earth and to differentiate between recycled crust and mantle origins of eclogite-hosted sulphides, including the precious metals that they capture. We present multiple sulphur isotope ratio measurements by secondary ion mass spectrometry for sulphides from a collection of mantle-derived eclogite xenoliths from Proterozoic and Mesozoic kimberlite occurrences in South Africa (Premier, Roberts Victor, Jagersfontein). Previous work established that the host eclogites have elemental and oxygen isotopic compositions in support of seawater-altered oceanic lithosphere protoliths, and for many of these xenolith suites Archean ages have been suggested.
The eclogite-hosted sulphides have values from −5.7 to , with the upper end of this wide range representing the highest-ever recorded composition of material derived from the Earth's mantle. The values range from −0.29 to and do not record significant mass-independent sulphur isotope fractionation, i.e., there is no compelling S-MIF signature. Most of the sulphide grains have values that fall within a range between −6 and , and they probably retain an isotopic record of sulphides that formed originally within altered oceanic crust. In contrast, the highly positive values from +13 to detected in sulphide grains from a single eclogite xenolith are similar to those of marine sulphates, which were probably a minor sulphur component of the oceanic crustal protolith. The lack of a significant S-MIF signature in the eclogitic sulphides that show evidence for a recycled crust origin implies that this sulphur component stems from a post-Archean surficial reservoir. This finding suggests that the cratonic mantle eclogites may have formed from post-Archean oceanic crust (e.g., Paleoproterozoic eclogite protoliths), or – as is preferred here – the ‘surficial’ sulphur was introduced into the cratonic root during relatively young metasomatic events and is thus unrelated to eclogite petrogenesis and Archean continent formation.
中文翻译:
克拉通地幔榴辉岩硫化物中的硫同位素(δ34S 和 Δ33S):古代俯冲带挥发性循环的一瞥
来自 Kaapvaal 克拉通地幔榴辉岩的硫化物的多种硫同位素组成允许阐明硫进入地球深处的循环,并区分榴辉岩承载的硫化物的循环地壳和地幔起源,包括它们捕获的贵金属。我们通过二次离子质谱法对来自南非元古代和中生代金伯利岩矿点(Premier、Roberts Victor、Jagersfontein)的幔源榴辉岩包体中的硫化物进行了多种硫同位素比测量。先前的工作确定寄主榴辉岩具有元素和氧同位素组成来支持海水改变的海洋岩石圈原岩,并且对于这些包体中的许多套件,已经提出太古宙年龄。
以榴辉岩为主体的硫化物具有 值从 -5.7 到 ,这个宽范围的上限代表有史以来最高的 来自地幔的物质组成。这 值范围从 -0.29 到 并且没有记录显着的与质量无关的硫同位素分馏,即没有引人注目的 S-MIF 特征。大多数硫化物颗粒具有 介于 -6 和 ,并且它们可能保留了最初在改变的洋壳中形成的硫化物的同位素记录。相比之下,高度积极的 值从 +13 到 在单个榴辉岩包体的硫化物颗粒中检测到的硫与海洋硫酸盐相似,后者可能是海洋地壳原岩中的少量硫成分。榴辉岩硫化物中缺乏显着的 S-MIF 特征,表明 循环地壳起源的证据表明,这种硫成分来自 太古代后地表水库。这一发现表明,克拉通地幔榴辉岩可能是由太古宙后洋壳形成的(例如,古元古代榴辉岩原岩),或者——正如这里优选的那样——在相对年轻的交代事件期间,“地表”硫被引入克拉通根部,并且因此与榴辉岩成因和太古代大陆形成无关。