Description: Spatial geochemical zonation is being increasingly recognized in Pacific and Atlantic hotspot tracks and is believed to reflect zonation within plumes upwelling from the margins of the Large Low Shear Velocity Provinces (LLSVPs) at the base of Earth’s mantle. We present new 40Ar/39Ar age data for the Discovery Rise (South Atlantic Ocean) that show an age progression in the direction of plate motion from 23Ma in the southwest to 40Ma in the northeast of the Rise, consistent with formation of the Rise above a mantle plume. The lavas have incompatible element and Sr–Nd–Pb–Hf radiogenic isotope characteristics similar to the enriched DUPAL anomaly occurring in the southern hemisphere. The northern chain of seamounts is compositionally similar to the adjacent Gough subtrack of the bilaterally-zoned Tristan–Gough hotspot track, whereas the southern chain has some of the most extreme DUPAL compositions found in South Atlantic intraplate lavas thus far. The nearby southern Mid-Atlantic Ridge, believed to interact with the Discovery hotspot, shows a similar spatial geochemical distribution, consistent with the Discovery hotspot being zoned over its entire 40Ma history. Our study implies a deep origin for the DUPAL anomaly, suggesting recycling of subcontinental lithospheric mantle (±lower crust) and oceanic crust through the lower mantle. The presence of an additional (Southern Discovery) DUPAL-like component, in addition to the Tristan and Gough/Northern Discovery components, in long-term zoned South Atlantic hotspots, points to the presence of a third lower mantle reservoir and thus is not consistent with the simple model that bilaterally-zoned plumes sample a chemically distinct LLSVP and the ambient mantle outside of the LLSVP.

Description: Highlights • Mantle plumes have broadly distinctive depleted and enriched compositions. • The Earth's lower mantle has a non-chondritic composition. • The deep mantle has large planetary-scale geochemical heterogeneity. • New normalising factors presented for modelling mantle-derived igneous rocks. Abstract Determining the composition and geochemical diversity of Earth's deep mantle and subsequent ascending mantle plumes is vital so that we can better understand how the Earth's primitive mantle reservoirs initially formed and how they have evolved over the last 4.6 billion years. Further data on the composition of mantle plumes, which generate voluminous eruptions on the planet's surface, are also essential to fully understand the evolution of the Earth's hydrosphere and atmosphere with links to surface environmental changes that may have led to mass extinction events. Here we present new major and trace element and Sr–Nd–Pb–Hf isotope data on basalts from Curacao, part of the Caribbean large igneous province. From these and literature data, we calculate combined major and trace element compositions for the mantle plumes that generated the Caribbean and Ontong Java large igneous provinces and use mass balance to determine the composition of the Earth's lower mantle. Incompatible element and isotope results indicate that mantle plumes have broadly distinctive depleted and enriched compositions that, in addition to the numerous mantle reservoirs already proposed in the literature, represent large planetary-scale geochemical heterogeneity in the Earth's deep mantle that are similar to non-chondritic Bulk Silicate Earth compositions.

Description: In contrast to the long narrow volcanic chains in the Pacific Ocean, Atlantic hotspot tracks, in particular in the South Atlantic (e.g., Tristan-Gough, Discovery, Shona, and Bouvet), are irregular and, in some cases, diffuse and discontinuous. An important question is whether this irregularity results from tectonic dismemberment of the tracks or if it represents differences in the size, structure, and strength of the melting anomalies. Here we present new age and geochemical data from volcanic samples from Richardson Seamount, Agulhas Ridge along the Agulhas-Falkland Fracture Zone (AFFZ), and Meteor Rise. Six samples yielded ages of 83–72 Ma and are 10–30 m.y. younger than the underlying seafloor, indicating that they are not on-axis seamounts associated with seafloor spreading. The incompatible element and Sr-Nd-Pb-Hf isotopic compositions range from compositions similar to those of the Gough domain of the nearby Tristan-Gough hotspot track to compositions similar to samples from the Shona bathymetric and geochemical anomaly along the southern Mid-Atlantic Ridge (49°–55°S), indicating the existence of a Shona hotspot as much as 84 m.y. ago and its derivation from a source region similar to that of the Tristan-Gough hotspot. Similar morphology, ages, and geochemistry indicate that the Richardson, Meteor, and Orcadas seamounts originally formed as a single volcano that was dissected and displaced 3500 km along the AFFZ, providing a dramatic example of how plate tectonics can dismantle and disseminate a hotspot track across an ocean basin.

Description: R/V Meteor cruise M81/2 mapped and sampled two prominent submarine structures of the Caribbean Plate: the Beata Ridge and the Hess Escarpment. While the Beata Ridge is commonly believed to be part of the Caribbean Large Igneous Province (CLIP), no comprehensive survey of the Hess Escarpment exists and thus its origin remains unclear. We present major element, trace element and Sr-Nd-Hf-Pb isotope data as well as 40Ar/39Ar age data including the first representative geochemical dataset for the Hess Escarpment. Unlike the proposition that the Hess Escarpment is part of the continental Chortis Block, our results show that the structure is of volcanic origin and most likely also belongs to the CLIP. The volcanic nature is also confirmed by its morphology. The Hess Escarpment represents a large fault zone but, including the area north of the Escarpment, it also consists of seamounts, guyots and ridges often located on huge plateau-like structures. Our preliminary age determinations of Beata Ridge samples yield an age range from 94 to 86 Ma lying well within the assumed main CLIP event at 89±6 Ma that is commonly believed to be formed by large degrees of melting of a starting plume head. However, three analyses with younger ages of 79, 63 and 51 Ma question the hypothesis that large igneous provinces are the result of catastrophic short-termed magmatic events and instead support the model of prolonged volcanism over tens of millions of years with several magmatic pulses. The geochemical data show that the Beata Ridge has compositions typical for the CLIP with flat chondrite-normalized rare earth element (REE) patterns (average (La/Yb)N = 1.15) and intermediate radiogenic isotope ratios, but enriched and depleted signatures are observed as well. The Hess Escarpment, in contrast, displays mainly depleted compositions partly more depleted than normal mid ocean ridge basalt (MORB) compositions and similar to the highly depleted komatiites of Gorgona Island. The results imply that the mantle source is heterogeneous and contains two components: a highly depleted component, in our data represented in samples from the Hess Escarpment, and an enriched component trending towards HIMU compositions, which we found only on the Beata Ridge. The typical CLIP isotopic compositions can be generated by mixing of melts from the two components. We further show that these heterogeneities can occur on a small scale of only tens of kilometers within the CLIP.

Description: In contrast to the long narrow volcanic chains in the Pacific, Atlantic hotspot tracks, in particular in the South Atlantic, e.g. Tristan-Gough, Discovery, Shona and Bouvet, are irregular and in some cases diffuse and discontinuous. An important question is whether this irregularity results from tectonic dismemberment of the tracks or if it represents differences in the size, structure and strength of the melting anomalies. Here we present new age and geochemical data from volcanic samples from Richardson Seamount, the Agulhas Ridge along the Agulhas-Falkland Fracture Zone (AFFZ) and Meteor Rise. Six samples yielded ages of 83-72 Myr and are 10-30 Myr younger than the underlying seafloor, indicating that they are not on-axis seamounts associated with sea-floor spreading. The incompatible element and Sr-Nd-Pb-Hf isotopic compositions rangefrom compositions similar to those of the Gough domain of the nearby Tristan-Gough hotspot track to compositions similar to samples from the Shona bathymetric and geochemical anomaly along the southern Mid-Atlantic Ridge (49-55°S), indicating the existence of a Shona hotspot as much as 84 Myr ago and its derivation from a similar source region similar to that of the Tristan-Gough hotspot. Similar morphology, ages and geochemistry indicate that Richardson, Meteor and Orcadas guyots originally formed as a single volcano that has been dissected and displaced 3500 km along the AFFZ, providing a dramatic example of how plate tectonics can dismantle and disseminate a hotspot track across an ocean basin.