High-pressure elastic properties of dolomite melt supporting carbonate-induced melting in deep upper mantle
High-pressure elastic properties of dolomite melt supporting carbonate-induced melting in deep upper mantle
复制标题
DOI：
10.1073/pnas.2004347117
复制
发表时间：
2020-07
影响因子：
11.1
通讯作者：
Man Xu;Z. Jing;S. Bajgain;M. Mookherjee;James A. Van Orman;Tony Yu;Yanbin Wang
中科院分区：
文献类型：
--
作者：
Man Xu;Z. Jing;S. Bajgain;M. Mookherjee;James A. Van Orman;Tony Yu;Yanbin Wang
意义 岩石学研究表明，富含碳酸盐的熔体存在于地球上地幔中，并在深层碳循环中发挥着重要作用。然而，由于缺乏对碳酸盐熔体弹性特性的了解，对这些熔体的地震探测很困难。在这里，我们利用高压实验和理论模拟确定了上地幔条件下白云石熔体的声速和密度。使用这些新的弹性数据计算出的含碳酸盐熔体地幔的速度与全球地震观测结果进行了比较。结果表明，~0.05%的富含碳酸盐熔体普遍存在于上地幔深处，这意味着全球平均地幔碳浓度为80-140 ppm。深俯冲碳酸盐岩可能导致上地幔低度熔融，从而在深部碳循环中发挥重要作用。然而，由于我们对碳酸盐熔体的弹性特性知之甚少，对地球内部碳酸盐引起的部分熔体的直接地震探测受到阻碍。在这里，我们报告了首次通过原位超声波和沉浮技术分别测定的白云石熔体的声速和密度数据，分别为 5.9 GPa 和 2046 K，以及白云石熔体高达 16 GPa 和 3000 K 的第一原理分子动力学模拟。使用我们的新弹性数据，计算出上地幔深部的 VP/VS 比 （~180-330 km）含有少量富含碳酸盐的熔体，为全球地震观测中上地幔的 VP/VS 比率升高提供了自然的解释，支持普遍存在低度富含碳酸盐的部分熔体（~0.05%），这与上地幔中挥发性诱发或氧化还原调节的初始熔体一致。 通过岩石学研究。这个富含碳酸盐的部分熔融区域意味着全球平均碳 (C) 浓度为 80–140 ppm。上地幔源区深层的重量比，与地球化学研究确定的地幔碳含量一致。
Significance Petrologic studies suggest that carbonate-rich melts are present in the Earth’s upper mantle and play an important role in the deep carbon cycle. However, seismic detection of these melts is difficult due to the lack of understanding of the elastic properties of carbonate melts. Here we determined the sound velocity and density of dolomite melt at upper mantle conditions using high-pressure experiments and theoretical simulations. The calculated velocities of carbonate melt-bearing mantle using these new elasticity data were compared with global seismic observations. The result suggests that ∼0.05% carbonate-rich melt can be pervasively present in the deep upper mantle, implying a global average mantle carbon concentration of 80-140 ppm. Deeply subducted carbonates likely cause low-degree melting of the upper mantle and thus play an important role in the deep carbon cycle. However, direct seismic detection of carbonate-induced partial melts in the Earth’s interior is hindered by our poor knowledge on the elastic properties of carbonate melts. Here we report the first experimentally determined sound velocity and density data on dolomite melt up to 5.9 GPa and 2046 K by in-situ ultrasonic and sink-float techniques, respectively, as well as first-principles molecular dynamics simulations of dolomite melt up to 16 GPa and 3000 K. Using our new elasticity data, the calculated VP/VS ratio of the deep upper mantle (∼180–330 km) with a small amount of carbonate-rich melt provides a natural explanation for the elevated VP/VS ratio of the upper mantle from global seismic observations, supporting the pervasive presence of a low-degree carbonate-rich partial melt (∼0.05%) that is consistent with the volatile-induced or redox-regulated initial melting in the upper mantle as argued by petrologic studies. This carbonate-rich partial melt region implies a global average carbon (C) concentration of 80–140 ppm. by weight in the deep upper mantle source region, consistent with the mantle carbon content determined from geochemical studies.