Petrological studies of Siberian Traps and associated alkaline rocks reveal high temperatures (1600-1650 o C) 14,17 in their mantle sources. Olivine compositions in samples from lower units of the Norilsk lava section provide evidence that the mantle source of the Siberian Traps was unusually rich in ancient recycled oceanic crust 14 in agreement with earlier predictions 10 . For the main volcanic phase, however, such data were unavailable. Here we report 2500 new olivine analyses and host-rock compositions for 45 basalts covering the main stages of 3 tholeiitic magmatism in three key localities: the Norilsk area, the Putorana plateau and the Maymecha-Kotuy province (Fig. 1). Almost all olivine compositions possess significantly higher NiO and FeO/MnO than expected for olivine in peridotite-derived magmas (Fig.1b,c supplementary Fig. S1), suggesting a contribution of melts from pyroxenitic sources 18 . Alternative explanations of these observations seem less plausible (see Methods for discussion). Our interpretation of the olivine compositions implies that the source of the Siberian Traps contained 10-20 wt.% recycled oceanic crust (Methods). More specifically, all lavas erupted during the first stage of magmatic activity (Gudchikhinskaya and earlier suits of the Norilsk area) are depleted in heavy rare earth elements (HREE) 19,20 indicating residual garnet and derivation within or below the base of thick lithosphere (>130 km) 14 . The source of Gudchikhinskaya lavas was likely almost entirely pyroxenitic 14 (Fig. 1b,c,d).Younger magmas are not depleted in HREE indicating formation at shallow depths and dramatic thinning of the lithosphere. Our calculation suggests that these magmas had a near-constant proportion of pyroxenite-derived melt of about 50% (Fig. 1d, table S1 in Supplementary Information) and were strongly contaminated by the continental crust 20 . Because the main Norilsk section spans less than 1 m.y. 1 , it is likely that the lithosphere was thinned in only a few hundred thousand years.High mantle temperatures over a vast area (Fig.1a) are consistent with the head of a hot mantle plume 6,9,17 . Based on the petrological constraints we develop a thermomechanical model of the interaction of the plume and lithosphere (see Methods). We assume that the plume arrived below the lithosphere at about 253 Ma (model time 0), perhaps near the northern border of the Siberian Shield, where the hottest melts (meimechites) erupted 17 . We further assume that the plume head was hot (Tp=1600°C, 250°C excess temperature) and contained a high content (15 wt.%.) of recycled oceanic crust. In our two-dimensional model, we approximate the plume head by a half-circle of 400 km radius located below cratonic lithosphere of variable thickness corresponding to the margin of the The arrival of a large and hot mantle plume head at the base of the lithosphere has been predicted 6,21 to cause about 0.8-1 km of broad surface uplift per 100°C of plume excess temperature. For a purely thermal plume with an excess temperature of 25...

GF is high and melt water is present under ice cover [11][12] Greenland to explain the origin of the observed melting beneath the ice cover (Figure 1). This are controlled by a combination of GF and non-GF influences, we build our calibration 137 strategy on estimating GF required to reproduce the observed thawed basal ice conditions, 138 discounting basal ice melt rates as a proxy for GF. This has the effect that GF estimates will 139 likely be biased downwards where basal melt is rapid; nevertheless, our strategy is 140 sufficiently effective to separate out the signal of a strong and spatially extensive geothermal 141 anomaly beneath the GIS and provides a hard lower bound for GF values at the observed 142 basal melt locations. 143The anomalous GF zone lies in the area with the highest density of direct measurements. 150One potential cause of elevated GF is illustrated by seismic data that link our west-to-east GF 151anomaly with a zone of low-seismic-velocity mantle, a "negative anomaly", beneath Iceland 6- Greenland may be the expression of Iceland hotspot history. The geothermal anomaly 237 provides evidence for a more northerly hotspot track than previously proposed and will offer 238 a useful test for existing paleoreconstructions of absolute plate motion. This study advocates 239 a previously undocumented strong coupling between Greenland's present-day ice dynamics, 240 subglacial hydrology, and the remote tectonothermal history of the North Atlantic region.

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