CO3+1 network formation in ultra-high pressure carbonate liquids
CO3+1 network formation in ultra-high pressure carbonate liquids
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DOI：
10.1038/s41598-019-51306-6
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发表时间：
2019-10
影响因子：
4.6
通讯作者：
M. Wilding;P. Bingham;M. Wilson;Y. Kono;J. W. Drewitt;R. Brooker;J. Parise
中科院分区：
文献类型：
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作者：
M. Wilding;P. Bingham;M. Wilson;Y. Kono;J. W. Drewitt;R. Brooker;J. Parise
碳酸盐液体是一类重要的熔盐，不仅用于工业应用，而且在地质过程中也有应用。就碳酸盐分子阴离子和金属阳离子之间的离子相互作用而言，碳酸盐通常被认为是简单的液体，因此与更“聚合”的硅酸盐熔体相比，碳酸盐相对没有结构。但是，从相关系、金属溶解度、玻璃光谱和模拟中，越来越多的证据表明，碳酸盐“网络”在长度尺度上的出现比组分分子阴离子长。众所周知，这些新兴结构的稳定性对温度很敏感，但也被预测会受到压力的影响。这一点很重要，因为最近的一项研究表明，俯冲的表面碳酸盐可能在地球的过渡带（~44公里）附近融化，这代表了深层碳循环的障碍，这取决于这些液体的浮力和粘度。在这项研究中，我们通过将模拟和碳酸盐玻璃（K2CO3-MgCO3）的高压测量相结合，证明了我们对碳酸盐液体的理解取得了重大进展，压力超过40 GPa，远远高于以往的任何研究。我们发现了紧密的CO32−对扩展的低维碳酸盐网络的清晰形成，以及“三加一”局部配位环境的出现，产生了意想不到的粘度随压力的增加。虽然碳酸盐岩熔体在下地幔中可能仍然是浮力的，但至少增加三个数量级的粘度将限制向上的流动性，可能导致被下行的板块夹带。
Carbonate liquids are an important class of molten salts, not just for industrial applications, but also in geological processes. Carbonates are generally expected to be simple liquids, in terms of ionic interactions between the molecular carbonate anions and metal cations, and therefore relatively structureless compared to more “polymerized” silicate melts. But there is increasing evidence from phase relations, metal solubility, glass spectroscopy and simulations to suggest the emergence of carbonate “networks” at length scales longer than the component molecular anions. The stability of these emergent structures are known to be sensitive to temperature, but are also predicted to be favoured by pressure. This is important as a recent study suggests that subducted surface carbonate may melt near the Earth’s transition zone (~44 km), representing a barrier to the deep carbon cycle depending on the buoyancy and viscosity of these liquids. In this study we demonstrate a major advance in our understanding of carbonate liquids by combining simulations and high pressure measurements on a carbonate glass, (K2CO3-MgCO3) to pressures in excess of 40 GPa, far higher than any previousin situstudy. We show the clear formation of extended low-dimensional carbonate networks of close CO32−pairs and the emergence of a “three plus one” local coordination environment, producing an unexpected increase in viscosity with pressure. Although carbonate melts may still be buoyant in the lower mantle, an increased viscosity by at least three orders of magnitude will restrict the upward mobility, possibly resulting in entrainment by the down-going slab.