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 V_P/V_S ratio of the deep upper mantle (∼180–330 km) with a small amount of carbonate-rich melt provides a natural explanation for the elevated V_P/V_S 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.

深度俯冲的碳酸盐可能引起上地幔的低度熔融，因此在深层碳循环中起重要作用。但是，由于我们对碳酸盐熔体的弹性特性缺乏了解，因此无法直接对地球内部的碳酸盐诱发的部分熔体进行地震探测。在这里，我们分别报告了通过原位超声和沉浮技术分别通过实验确定的高达5.9 GPa和2046 K的白云岩的声速和密度数据，以及报告了高达16的白云石熔体的第一性原理分子动力学模拟GPa和3000K。使用我们新的弹性数据，计算出的深上地幔（约180-330 km）中含有少量富含碳酸盐的熔体的V _P / V _S比为V的升高提供了自然的解释来自全球地震观测的上地幔的_P / V _S比，支持普遍存在的低度富含碳酸盐的部分熔体（约0.05％），这与上层中的挥发性诱导或氧化还原调节的初始熔体一致岩石学研究认为的地幔。这个富含碳酸盐的部分熔体区域意味着全球平均碳（C）浓度为80-140 ppm。在上地幔深源区的重量百分比，与根据地球化学研究确定的地幔碳含量一致。