Large oxygen excess in the primitive mantle could be the source of the Great Oxygenation Event
Large oxygen excess in the primitive mantle could be the source of the Great Oxygenation Event
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DOI：
10.7185/geochemlet.1801
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发表时间：
2018-01-01
影响因子：
4.9
通讯作者：
Hennet, L.
中科院分区：
文献类型：
--
作者：
Andrault, D.;Munoz, M.;Hennet, L.
在太古宙-元古宙过渡期（APT）之前，构造体制主要是浮在低粘度地幔上的微板块。这种机制限制了浅、深地幔储层之间的化学交换。在APT之后，一个更加全球性的对流机制导致板块的深俯冲。我们建议，改进的地幔垂直混合有利于释放到地球表面的氧过剩最初被困在地幔深处。当金属铁向下分离进入地核后，原始下地幔留下高的Fe 3 +/（Fe 2 + Fe 3+）比（#Fe 3+）时，这种过剩就形成了。我们的同步加速器原位实验表明，地幔铁的原始Fe 3+过剩量约为20%。与现今地幔的#Fe 3+相比，这种Fe（3+）过量相当于地球大气中O-2含量的500-1000倍。构造转型极大地促进了氧化的下地幔物质向地球表面的上升，导致O-2持续到达地球表面并进入大气层。
Before the Archean to Proterozoic Transition (APT) the tectonic regime was dominated by microplates floating on a low viscosity mantle. Such a regime restricted chemical exchange between the shallow and deeper mantle reservoirs. After the APT, a more global convection regime led to deep subduction of slabs. We propose that the improved vertical mixing of the mantle favoured the release to the Earth's surface of an oxygen excess initially trapped in the deep mantle. This excess built up when the primordial lower mantle was left with a high Fe3+/(Fe2+Fe3+) ratio (#Fe3+), after metallic iron segregated down into the core. Our synchrotron-based in situ experiments suggest a primordial Fe3+ excess of similar to 20 % for the mantle iron. By comparison with the #Fe3+ of the present mantle, this Fe(3+)excess would correspond to 500-1000 times the O-2 content in the Earth's atmosphere. The tectonic transition greatly facilitated the ascent of oxidised lower mantle material towards the Earth's surface, inducing a continuous arrival of O-2 at the Earth's surface and into the atmosphere.