Seafloor anomalies along mid-ocean ridges with exceptionally thick and compositionally distinct basaltic crust, for example, at Iceland, suggest that the underlying mantle is hotter and chemically different from the adjacent subridge mantle. Here we present hafnium and neodymium isotope ratios of peridotites from the Charlie Gibbs Transform Zone, which is located at the southern end of the Reykjanes Ridge south-west of Iceland. These peridotites are strongly depleted in incompatible elements with extremely high hafnium isotope ratios, suggesting that they had already melted to a large extent before being incorporated into the plume, at least 1 billion years ago, and thereby also became less dense. We argue that seismic velocity anomalies, geodynamic models and geochemical affinities of ridge basalts connect the peridotites from the Charlie Gibbs Transform Zone to the ‘Iceland plume’. The thermochemical buoyancy of the moderately hot Iceland plume, but also that of other plumes worldwide, may therefore be strongly influenced by composition. Variable peridotite depletion along the rising Iceland plume could also cause the transient, density-driven pulses in plume flux, which have formed the V-shaped Reykjanes Ridge south of Iceland. Overall, expansion of a ridge-centred plume along adjacent ridges and melting of heterogeneous plume material explains the topographic swell, the seismic anomaly and the formation of V-shaped ridges, as well as the regional distribution of basalts with Icelandic affinity.

沿着大洋中脊的海底异常，例如在冰岛，玄武岩地壳特别厚且成分不同，这表明下面的地幔温度更高，并且化学成分与邻近的山脊地幔不同。在这里，我们展示了来自查理吉布斯转变带的橄榄岩的铪和钕同位素比率，该转变带位于冰岛西南部雷克雅内斯山脊的南端。这些橄榄岩中的不相容元素严重匮乏，铪同位素比极高，这表明它们在被纳入羽流之前就已经在很大程度上融化了，至少在 10 亿年前，因此密度也降低了。我们认为地震速度异常、地球动力学模型和山脊玄武岩的地球化学亲和力将查理吉布斯转换带的橄榄岩与“冰岛羽流”连接起来。因此，中等温度的冰岛羽流的热化学浮力以及世界各地其他羽流的热化学浮力可能会受到成分的强烈影响。沿着上升的冰岛羽流的可变橄榄岩消耗也可能导致羽流通量中短暂的、密度驱动的脉冲，从而形成了冰岛南部的V形雷克雅内斯山脊。总体而言，以山脊为中心的羽流沿相邻山脊的扩张和异质羽流物质的融化解释了地形隆起、地震异常和V形山脊的形成，以及与冰岛有亲缘关系的玄武岩的区域分布。