Slab-derived devolatilization fluids oxidized by subducted metasedimentary rocks
Slab-derived devolatilization fluids oxidized by subducted metasedimentary rocks
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DOI：
10.1038/s41561-022-00904-7
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发表时间：
2022-03
影响因子：
18.3
通讯作者：
J. Ague;S. Tassara;M. Holycross;Ji‐Lei Li;E. Cottrell;E. Schwarzenbach;C. Fassoulas;T. John
中科院分区：
文献类型：
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作者：
J. Ague;S. Tassara;M. Holycross;Ji‐Lei Li;E. Cottrell;E. Schwarzenbach;C. Fassoulas;T. John
俯冲板片的变质脱挥发分作用产生上升进入地幔楔的含水流体，驱动产生弧岩浆的部分熔融。这些岩浆的氧逸度比大洋中脊产生的岩浆高出约10至1 000倍。这种氧化岩浆的性质是由板状流体赋予的，还是在上升过程中与周围的地幔或地壳相互作用而获得的，目前还存在争议。在这里，我们研究的变质沉积岩的岩石学从两个第三纪爱琴海俯冲复合体结合反应运输模型，以调查氧化电位的沉积岩覆盖板。我们发现，变质沉积岩保存的证据，流体介导的氧化还原反应，可以高度氧化。此外，建模表明，这些氧化岩石层厚度小于约200米有能力通过氧化还原反应，去除H2，CH 4和/或H2S的流体氧化上升板脱水通量。然后，这些流体可以氧化上覆地幔楔的速率与弧岩浆生成速率相当，主要是通过涉及硫的反应。氧化变质沉积岩本身不需要产生大量的流体，但可以氧化通过它们上升的板状脱水流体。弧岩浆氧逸度的建议中生代的增加可能反映了氧化风化产物的循环后，新元古代-古生代海洋和大气氧化。
Metamorphic devolatilization of subducted slabs generates aqueous fluids that ascend into the mantle wedge, driving the partial melting that produces arc magmas. These magmas have oxygen fugacities some 10–1,000 times higher than magmas generated at mid-ocean ridges. Whether this oxidized magmatic character is imparted by slab fluids or is acquired during ascent and interaction with the surrounding mantle or crust is debated. Here we study the petrology of metasedimentary rocks from two Tertiary Aegean subduction complexes in combination with reactive transport modelling to investigate the oxidative potential of the sedimentary rocks that cover slabs. We find that the metasedimentary rocks preserve evidence for fluid-mediated redox reactions and could be highly oxidized. Furthermore, the modelling demonstrates that layers of these oxidized rocks less than about 200 m thick have the capacity to oxidize the ascending slab dehydration flux via redox reactions that remove H2, CH4and/or H2S from the fluids. These fluids can then oxidize the overlying mantle wedge at rates comparable to arc magma generation rates, primarily via reactions involving sulfur species. Oxidized metasedimentary rocks need not generate large amounts of fluid themselves but could instead oxidize slab dehydration fluids ascending through them. Proposed Phanerozoic increases in arc magma oxygen fugacity may reflect the recycling of oxidative weathering products following Neoproterozoic–Palaeozoic marine and atmospheric oxygenation.