Experimental investigation of the stability of Fe-rich carbonates in the lower mantle
Experimental investigation of the stability of Fe-rich carbonates in the lower mantle
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DOI：
10.1029/2011jb008733
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发表时间：
2012-02-10
影响因子：
3.9
通讯作者：
Fiquet, G.
中科院分区：
文献类型：
--
作者：
Boulard, E.;Menguy, N.;Fiquet, G.
碳酸盐在地幔中的命运在地球动力碳循环中起着关键作用。虽然铁是地球下地幔的主要成分，但含铁碳酸盐的稳定性很少被研究。本文给出了富铁碳酸盐在压力为40~105 Gpa，温度为1450~3600K，对应于地球下地幔深度约1000~2400千米时稳定性的实验结果。将氧化铁和铁镁氧化物的样品装入二氧化碳气体中，并在金刚石顶压室中进行激光加热。用X射线衍射仪对产物进行了原位表征，并对回收的样品进行了分析和扫描电子显微镜研究。结果表明，Fe~(2+)参与了氧化还原反应，CO_2生成含Fe~(3+)相和金刚石。我们还报道了一个新的含Fe(III)的高压相，这是由于FeCO3在超过40 Gpa的压力下转变而产生的。钻石和氧化的含碳相的存在表明，氧化和还原形式的碳可能在深部地幔中共存。最后，观察到的反应可能为深部金刚石的形成提供了一种新的机制。
The fate of carbonates in the Earth's mantle plays a key role in the geodynamical carbon cycle. Although iron is a major component of the Earth's lower mantle, the stability of Fe-bearing carbonates has rarely been studied. Here we present experimental results on the stability of Fe-rich carbonates at pressures ranging from 40 to 105 GPa and temperatures of 1450-3600 K, corresponding to depths within the Earth's lower mantle of about 1000-2400 km. Samples of iron oxides and iron-magnesium oxides were loaded into CO2 gas and laser heated in a diamond-anvil cell. The nature of crystalline run products was determined in situ by X-ray diffraction, and the recovered samples were studied by analytical transmission electron microscopy and scanning transmission X-ray microscopy. We show that Fe-(II) is systematically involved in redox reactions with CO2 yielding to Fe-(III)-bearing phases and diamonds. We also report a new Fe-(III)-bearing high-pressure phase resulting from the transformation of FeCO3 at pressures exceeding 40 GPa. The presence of both diamonds and an oxidized C-bearing phase suggests that oxidized and reduced forms of carbon might coexist in the deep mantle. Finally, the observed reactions potentially provide a new mechanism for diamond formation at great depth.