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Intraplate magmatic provinces found away from plate boundaries provide direct sampling of the composition and heterogeneity of the Earth’s mantle. The chemical heterogeneities that have been observed in the mantle are usually attributed to recycling during subduction 1 – 3 , which allows for the addition of volatiles and incompatible elements into the mantle. Although many intraplate volcanoes sample deep-mantle reservoirs—possibly at the core–mantle boundary 4 —not all intraplate volcanoes are deep-rooted 5 , and reservoirs in other, shallower boundary layers are likely to participate in magma generation. Here we present evidence that suggests Bermuda sampled a previously unknown mantle domain, characterized by silica-undersaturated melts that are substantially enriched in incompatible elements and volatiles, and a unique, extreme isotopic signature. To our knowledge, Bermuda records the most radiogenic 206 Pb/ 204 Pb isotopes that have been documented in an ocean basin (with 206 Pb/ 204 Pb ratios of 19.9–21.7) using high-precision methods. Together with low 207 Pb/ 204 Pb ratios (15.5–15.6) and relatively invariant Sr, Nd, and Hf isotopes, the data suggest that this source must be less than 650 million years old. We therefore interpret the Bermuda source as a previously unknown, transient mantle reservoir that resulted from the recycling and storage of incompatible elements and volatiles 6 – 8 in the transition zone (between the upper and lower mantle), aided by the fractionation of lead in a mineral that is stable only in this boundary layer, such as K-hollandite 9 , 10 . We suggest that recent recycling into the transition zone, related to subduction events during the formation of Pangea, is the reason why this reservoir has only been found in the Atlantic Ocean. Our geodynamic models suggest that this boundary layer was sampled by disturbances related to mantle flow. Seismic studies and diamond inclusions 6 , 7 have shown that recycled materials can be stored in the transition zone 11 . For the first time, to our knowledge, we show geochemical evidence that this storage is key to the generation of extreme isotopic domains that were previously thought to be related only to deep recycling. The formation of Bermuda sampled a previously unknown mantle reservoir that is characterized by silica-undersaturated melts enriched in volatiles and by a unique lead isotopic signature, which suggests that the source is young.

The mid-Piacenzian is known as a period of relative warmth when compared to the present day. A comprehensive understanding of conditions during the Piacenzian serves as both a conceptual model and a source for boundary conditions as well as means of verification of global climate model experiments. In this paper we present the PRISM4 reconstruction, a paleoenvironmental reconstruction of the mid-Piacenzian ( ∼  3 Ma) containing data for paleogeography, land and sea ice, sea-surface temperature, vegetation, soils, and lakes. Our retrodicted paleogeography takes into account glacial isostatic adjustments and changes in dynamic topography. Soils and lakes, both significant as land surface features, are introduced to the PRISM reconstruction for the first time. Sea-surface temperature and vegetation reconstructions are unchanged but now have confidence assessments. The PRISM4 reconstruction is being used as boundary condition data for the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) experiments.

Sedimentary rocks from Virginia through Florida record marine flooding during the mid-Pliocene. Several wave-cut scarps that at the time of deposition would have been horizontal are now draped over a warped surface with a maximum variation of 60 meters. We modeled dynamic topography by using mantle convection simulations that predict the amplitude and broad spatial distribution of this distortion. The results imply that dynamic topography and, to a lesser extent glacial isostatic adjustment account for the current architecture of the coastal plain and proximal shelf. This confounds attempts to use regional stratigraphie relations as references for longer-term sea-level determinations. Inferences of Pliocene global sea-level heights or stability of Antarctic ice sheets therefore cannot be deciphered in the absence of an appropriate mantle dynamic reference frame.

Climate cycles fundamentally control surface processes that affect the distribution of water and sediment, and their associated loads, across the Earth's surface. Here, we use a geodynamic model to examine how water loading can affect mantle melt generation in continental rift settings covered by deep lakes. Our modeling results suggest that lake level fluctuations can modulate the timing and rate of mantle melting. A rapid lake level drop of 800 m has the potential to increase mantle melt volumes by enhancing mantle upwelling beneath the rift, whereas a lake level rise can lead to a reduction of mantle melting. The volume of melt produced driven by lake level fluctuations is also dependent on crustal rheology, extension rate, mantle potential temperature, and lithosphere thickness. Our study identifies the importance of water loading for controlling rift processes, while also demonstrating critical links between changing climate, rift evolution and mantle melting. Plain Language Summary The break‐up of continents produces subsidence and the formation of rift valleys and where the climate is favorable, rift lakes. Changes in effective moisture in response to climate changes drive water level fluctuations in rift lakes, and their associated loads. But our understanding of the interaction between hydroclimate changes and rift basin evolution remains limited. To address this, we employed a geodynamic model to explore how water loading can influence mantle melt production in continental rift environments. Our model suggests that lake level fluctuations can have a detectable effect on the timing and pace of mantle melting. A lake level drop can increase mantle melt volume by enhancing mantle upwelling underneath the rift, while a lake level rise can lead to a reduction in mantle melting. Additionally, the amount of melt produced by these fluctuations depends on factors such as crustal rheology, extension rate, thermal gradient, and lithosphere thickness. Our findings reveal the significance of water loading in governing rift processes and highlight the potential links between changing climate, rift evolution, and mantle melting. Key Points Lake level drops of 800 m can enhance decompressive mantle melting A case study for the Turkana Rift shows a correlation between lake level drops and enhanced volcanism over the last 4 Myr Sensitivity of mantle melting to lake loading is controlled by extension rate, mantle potential temperature, and lithosphere thickness

Ice streams are sites of ice-sheet drainage and together with other processes, such as calving, have an impact on deglaciation rates and ice-sheet mass balance. Proglacial lake deposits provide records of ice-sheet deglaciation and have the potential to supplement other paleoclimate records. Oneida Lake, northeastern USA, contains a thick proglacial lake sequence that buries evidence of ice streaming and a paleo-calving margin that developed during retreat of the Laurentide Ice Sheet. Previous high-resolution digital elevation models identified the Oneida Ice Stream from glacial landforms northwest of the lake. In this study, we utilize seismic refractions from a multichannel seismic (MCS) reflection dataset to estimate the thickness of glacial deposits using seismic tomography. With this method we constrain the depth to top of Paleozoic strata, especially in areas where the reflection data yielded poor outcomes and validate our reflection data in regions of good coverage. We demonstrate that where long offset seismic data are available, the first-arrival tomography method is useful in studies of formerly glaciated basins. Our study identifies a ~108 m thick sedimentary section and potentially long paleoclimate record in Oneida Lake, and identifies a paleotopographic low that likely encouraged formation of the Oneida Ice Stream.

Continental rifting is influenced by interactions between tectonic, magmatic, and surface processes, with the latter strongly dependent on regional climate. We test the role of regional climate variability on rift system behavior, by investigating fault slip rate changes in the South Turkana Basin (Lake Turkana Rift, northern Kenya) at the end of the African Humid Period. Throw rates on 27 faults examined during the African Humid Period (9,631–5,333 yr BP) and post-African Humid Period (5,333 yr BP–present) exhibit a mean 0.17 ± 0.08 mm/yr increase during the drier, post-African Humid Period. Numerical simulations reveal Coulomb stress changes from two loading sources that may explain these changes: (1) reduced vertical loading from a 100–150 m lake level drop, and (2) increased magmatic loading from enhanced mantle melt production due to reduced lake loading. An increase in magma flux of > 0.1 km 3 /kyr below the South Turkana Basin results in Coulomb stress changes exceeding those expected from a 100–150 m lake level drop. We provide the first empirical evidence of increased fault activity in response to climate-induced lake level changes in the East African Rift System over time scales of 10 3 –10 4  years, and reveal that climate-tectonic interactions are enhanced in magmatically active rift systems.

We introduce a quantitative model of global mantle convection that reconstructs the detailed motion of a warm mantle upwelling over the last 30 Ma towards the interior of the southwestern USA from observed present‐day mantle heterogeneity. The onset and evolution of uplift in the central Basin and Range province and Colorado Plateau during this time is determined by tracking the topographic swell due to this mantle upwelling. We show that: (1) the extension and basaltic volcanism (post 25 Ma) in the central Basin and Range coincides with the arrival and eastward progression of this upwelling, and (2) dynamic uplift of the southern Colorado Plateau, totaling about 1 km, transpired in the last 20 Ma. Since 10 Ma, the center of uplift continued northeastward from the southwestern rim of the plateau consistent with a young Grand Canyon model and eastward sweep of magmatism in the western Colorado Plateau.

Africa’s topography is characterized by large-scale uplifted domes and subsided basins. Numerical simulations of mantle flow suggest that high topography along Africa’s eastern margin formed as a result of the northward migration of the tectonic plate over the African superplume during the past 30 million years. The topography of the African continent is characterized by large-scale extensional features such as the East African Rift, widespread volcanic activity, and anomalously subsided basins and uplifted domes 1 . These enigmatic surface features have long suggested that the African continent is shaped by significant dynamic forcing originating in the underlying mantle 2 , 3 , 4 . Here we simulate mantle convection backwards in time to reconstruct the evolution of dynamic topography of Africa over the past 30 million years. We show that the current high topography of the East African Rift system is due to the southward propagation of a topographic swell that encompassed the western margin of Arabia and the Afar region before 30 million years ago. We suggest that this dominant swell formed in response to the upwelling of the African superplume and the relative northward motion of the African tectonic plate over it. We also find that the adjacent Congo Basin has gradually subsided over the same time period in response to convective drawdown in the mantle. We conclude that much of Africa’s recent geological history is driven by buoyancy forces in the mantle. Our findings have important implications for African volcanism, erosion, sediment transport and river-basin drainage patterns 4 , 5 , 6 .

Continental flood basalt lavas often contain deeply-sourced, thermo-chemically anomalous material that can provide a potential probe of inaccessible reservoirs. However, continental flood basalts interact with geochemically diverse domains within the continental lithosphere, which may complicate interpretations of deep mantle signatures. We examine the role of continental lithospheric mantle in continental flood basalts erupted as part of the 1.1 Ga Keweenawan large igneous province, centered on the Lake Superior region of North America. We show that flood basalts at Mamainse Point exhibit a range of εHf 1100 from −14.1 to +6, plotting along the global εHf—εNd mantle array. Lithospheric mantle melts represented by alkaline rocks from the Coldwell and Seabrook Lake Complexes yield positive εNd 1100 (+0.7 to +4.3) and εHf 1100 from −6.9 to +2.4, placing them below the mantle array. Mamainse Point lavas are interpreted to be variably crustally contaminated melts of the Keweenawan plume and ambient upper mantle; there is no clear evidence for contributions from an enriched lithospheric mantle.