Cumulate causes for the low contents of sulfide-loving elements in the continental crust
Cumulate causes for the low contents of sulfide-loving elements in the continental crust
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DOI：
10.1038/ngeo2965
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发表时间：
2017-07-01
影响因子：
18.3
通讯作者：
Jenner, Frances Elaine
中科院分区：
文献类型：
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作者：
Jenner, Frances Elaine
尽管亲铜（喜欢硫化物）和亲铁（喜欢金属）元素（CSE）具有经济重要性，但与大洋地壳相比，它们如何在大陆地壳中富集或贫化尚不清楚。这部分是由于我们对CSE的分区行为的理解有限。在这里，我收集了大洋中脊玄武岩和与俯冲有关的火山岩的成分数据。我表明，幔源熔体，有助于海洋和大陆地壳的形成很少避免硫化物饱和在地壳冷却过程中，平均而言，俯冲带岩浆fractionary硫化物在大陆地壳的基础上上升之前。与上地壳相比，幔源熔体的分异使某些CSE中的下地壳含硫化物和硅酸盐堆晶富集。这种存储倾向于堆积物中的相容CSE（如Cu和Au）在俯冲和拆沉过程中再循环回地幔，导致其在大块陆壳中的含量较低，并可能导致上陆壳矿床的稀缺。与此相反，分异作用导致大洋和大陆上地壳与大洋和大陆下地壳相比，变得富含不相容的CSE（如W）。因此，不相容的CSE倾向于富集于俯冲带岩浆，这有助于大陆地壳的形成，并且与相容的CSE相比，不太容易通过分层从大陆地壳中去除。
Despite the economic importance of chalcophile (sulfide-loving) and siderophile (metal-loving) elements (CSEs), it is unclear how they become enriched or depleted in the continental crust, compared with the oceanic crust. This is due in part to our limited understanding of the partitioning behaviour of the CSEs. Here I compile compositional data for mid-ocean ridge basalts and subduction-related volcanic rocks. I show that the mantle-derived melts that contribute to oceanic and continental crust formation rarely avoid sulfide saturation during cooling in the crust and, on average, subduction-zone magmas fractionate sulfide at the base of the continental crust prior to ascent. Differentiation of mantle-derived melts enriches lower crustal sulfide-and silicate-bearing cumulates in some CSEs compared with the upper crust. This storage predisposes the cumulate-hosted compatible CSEs (such as Cu and Au) to be recycled back into the mantle during subduction and delamination, resulting in their low contents in the bulk continental crust and potentially contributing to the scarcity of ore deposits in the upper continental crust. By contrast, differentiation causes the upper oceanic and continental crust to become enriched in incompatible CSEs (such as W) compared with the lower oceanic and continental crust. Consequently, incompatible CSEs are predisposed to become enriched in subduction-zone magmas that contribute to continental crust formation and are less susceptible to removal from the continental crust via delamination compared with the compatible CSEs.