The fate of carbonate in oceanic crust subducted into earth's lower mantle
The fate of carbonate in oceanic crust subducted into earth's lower mantle
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DOI：
10.1016/j.epsl.2019.01.041
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发表时间：
2019-04-01
影响因子：
5.3
通讯作者：
Kleppe, Annette K.
中科院分区：
文献类型：
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作者：
Drewitt, James W. E.;Walter, Michael J.;Kleppe, Annette K.
我们报告了在FeO-MgO-SiO2-CO2（FMSC）和CaO-MgO-SiO2-CO2（CMSC）系统中进行的激光加热金刚石对顶砧（LHDAC）实验，旨在测试下地幔压力下的脱碳和金刚石形成反应。基于合成实验的亚固相线相关系被报道在类似于35至90 GPa的压力范围和类似于1600至2200 K的温度下。构建由碳酸盐和二氧化硅的混合物组成的三元本体组合物，使得脱碳反应产生非三元相（例如，硼镁石、Ca-钙钛矿、金刚石、CO2-V），并且使用同步加速器X射线衍射和显微拉曼光谱来鉴定反应产物的外观。我们发现，在这两个系统中的碳酸盐相与二氧化硅反应，形成bridgmanite +/-Ca-钙钛矿+ CO2在压力范围内类似于40至70 GPa和1600至1900 K的负克拉珀龙斜率的脱碳反应。我们的研究结果表明，脱碳反应形成了一个不可逾越的障碍，在大洋地壳的碳酸盐俯冲到地幔深度大于类似1500公里。我们还确定了碳酸盐和CO2-V分解反应，形成金刚石加氧。根据所观察到的脱碳酸反应，我们预测，俯冲到下地幔深部的洋壳中碳酸盐的最终命运是在下地幔最深处沿沿着板状地热和整个下地幔沿沿着地幔地热以难熔金刚石的形式存在。在大洋地壳中通过亚固相线脱碳作用产生的金刚石是耐火的和不流动的，可以在很长的时间尺度上储存在地幔底部，可能会在与深部地幔柱相关的OIB岩浆中返回到地表。(C)2019作者由Elsevier B. V.发布，这是CC BY许可下的开放获取文章。
We report on laser-heated diamond anvil cell (LHDAC) experiments in the FeO-MgO-SiO2-CO2 (FMSC) and CaO-MgO-SiO2-CO2 (CMSC) systems at lower mantle pressures designed to test for decarbonation and diamond forming reactions. Sub-solidus phase relations based on synthesis experiments are reported in the pressure range of similar to 35 to 90 GPa at temperatures of similar to 1600 to 2200 K. Ternary bulk compositions comprised of mixtures of carbonate and silica are constructed such that decarbonation reactions produce non-ternary phases (e.g. bridgmanite, Ca-perovskite, diamond, CO2-V), and synchrotron X-ray diffraction and micro-Raman spectroscopy are used to identify the appearance of reaction products. We find that carbonate phases in these two systems react with silica to form bridgmanite +/- Ca-perovskite + CO2 at pressures in the range of similar to 40 to 70 GPa and 1600 to 1900 K in decarbonation reactions with negative Clapeyron slopes. Our results show that decarbonation reactions form an impenetrable barrier to subduction of carbonate in oceanic crust to depths in the mantle greater than similar to 1500 km. We also identify carbonate and CO2-V dissociation reactions that form diamond plus oxygen. On the basis of the observed decarbonation reactions we predict that the ultimate fate of carbonate in oceanic crust subducted into the deep lower mantle is in the form of refractory diamond in the deepest lower mantle along a slab geotherm and throughout the lower mantle along a mantle geotherm. Diamond produced in oceanic crust by subsolidus decarbonation is refractory and immobile and can be stored at the base of the mantle over long timescales, potentially returning to the surface in OIB magmas associated with deep mantle plumes. (C) 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license.