Carbon in the upper mantle controls incipient melting of carbonated peridotite and so acts as a critical driver of plate tectonics. The carbon-rich melts that form control the rate of volatile outflux from the Earth’s interior, contributing to climate evolution over geological times. However, attempts to constrain the carbon concentrations of the mantle source beneath oceanic islands and continental rifts is complicated by pre-eruptive volatile loss from magmas. Here, we compile literature data on magmatic gases, as a surface expression of the pre-eruptive volatile loss, from 12 oceanic island and continental rift volcanoes. We find that the levels of carbon enrichment in magmatic gases correlate with the trace element signatures of the corresponding volcanic rocks, implying a mantle source control. We use this global association to estimate that the mean carbon concentration in the upper mantle, down to 200 km depth, is approximately 350 ppm (range 117–669 ppm). We interpret carbon mantle heterogeneities to reflect variable extents of mantle metasomatism from carbonated silicate melts. Finally, we find that the extent of carbon enrichment in the upper mantle positively correlates with the depth at which melting starts. Our results imply a major role of carbon in driving melt formation in the upper mantle.

上地幔中的碳控制着碳酸盐橄榄岩的初期熔融，因此是板块构造的关键驱动因素。形成的富含碳的熔体控制着从地球内部流出的挥发性物质的速率，有助于地质时期的气候演变。然而，限制大洋岛屿和大陆裂谷下方地幔源碳浓度的尝试由于岩浆喷发前的挥发性损失而变得复杂。在这里，我们汇编了来自 12 个海洋岛屿和大陆裂谷火山的岩浆气体文献数据，作为喷发前挥发性损失的表面表达。我们发现岩浆气体中的碳富集水平与相应火山岩的微量元素特征相关，这意味着地幔源控制。我们使用这个全球关联来估计上地幔中的平均碳浓度，下至 200 公里深度，约为 350 ppm（范围 117-669 ppm）。我们解释碳地幔的非均质性以反映来自碳酸盐硅酸盐熔体的地幔交代作用的不同程度。最后，我们发现上地幔中碳的富集程度与熔融开始的深度正相关。我们的结果表明碳在推动上地幔熔体形成中的主要作用。我们发现上地幔中碳的富集程度与熔融开始的深度正相关。我们的结果表明碳在推动上地幔熔体形成中的主要作用。我们发现上地幔中碳的富集程度与熔融开始的深度正相关。我们的结果表明碳在推动上地幔熔体形成中的主要作用。