Plume magmatism and continental breakup led to the opening of the northeast Atlantic Ocean during the globally warm early Cenozoic. This warmth culminated in a transient (170 thousand year, kyr) hyperthermal event associated with a large, if poorly constrained, emission of carbon called the Palaeocene–Eocene Thermal Maximum (PETM) 56 million years ago (Ma). Methane from hydrothermal vents in the coeval North Atlantic Igneous Province (NAIP) has been proposed as the trigger, though isotopic constraints from deep sea sediments have instead implicated direct volcanic carbon dioxide (CO₂) emissions. Here we calculate that background levels of volcanic outgassing from mid-ocean ridges and large igneous provinces yield only one-fifth of the carbon required to trigger the hyperthermal. However, geochemical analyses of volcanic sequences spanning the rift-to-drift phase of the NAIP indicate a sudden ~220 kyr-long intensification of magmatic activity coincident with the PETM. This was likely driven by thinning and enhanced decompression melting of the sub-continental lithospheric mantle, which critically contained a high proportion of carbon-rich metasomatic carbonates. Melting models and coupled tectonic–geochemical simulations indicate that >10⁴ gigatons of subcrustal carbon was mobilized into the ocean and atmosphere sufficiently rapidly to explain the scale and pace of the PETM.

在全球温暖的新生代早期，羽流岩浆作用和大陆分裂导致东北大西洋的开放。这种温暖在一个短暂的（17 万年，kyr）过热事件中达到顶峰，该事件与 5600 万年前（Ma）发生的被称为古新世-始新世热最大值（PETM）的大量碳排放（如果限制很差）相关。来自同期北大西洋火成岩省 (NAIP) 热液喷口的甲烷被提议作为触发因素，尽管来自深海沉积物的同位素限制反而暗示了直接火山二氧化碳 (CO ₂) 排放。在这里，我们计算出大洋中脊和大型火成岩省火山释气的背景水平仅产生触发超高温所需碳的五分之一。然而，跨越 NAIP 裂谷到漂移阶段的火山序列的地球化学分析表明，与 PETM 一致的岩浆活动突然增强了约 220 kyr。这可能是由次大陆岩石圈地幔的变薄和减压熔融所驱动的，该地幔关键地含有高比例的富碳交代碳酸盐。熔融模型和耦合的构造-地球化学模拟表明，超过 10 ⁴吉吨的地壳下碳以足够快的速度迁移到海洋和大气中，足以解释 PETM 的规模和速度。