Description: Multibeam bathymetry raw data was recorded in the South-West Pacific during cruise SO255 that took place between 2017-03-02 and 2017-04-14. The data was collected using the ship's own Kongsberg EM 122. A sound velocity profile (SVP) was applied on the data for calibration. SVP data are part of this dataset publication. This data has been contributed to the DAM (German Marine Research Alliance) underway research data project.

Description: Multibeam bathymetry raw data was recorded in the South-West Pacific during cruise SO255 that took place between 2017-03-02 and 2017-04-14. The data was collected using the ship's own Kongsberg EM 710. A sound velocity profile (SVP) was applied on the data for calibration. SVP data are part of this dataset publication. This data has been contributed to the DAM (German Marine Research Alliance) underway research data project.

Description: Despite their large number and in contrast to seamount chains, small solitary seamounts/seamount groups have rarely been sampled and therefore their origins remain enigmatic. Here we present 40Ar/39Ar, trace element and Nd‐Pb‐Hf isotope data from the solitary Demenitskoy Seamount, the isolated Tolkien seamount group and the Krylov Seamount and Ridge in the Canary Basin. Their chemical compositions range from intraplate ocean‐island‐basalt (Demenitskoy) to normal‐ and enriched‐mid‐ocean‐ridge‐basalt types (Tolkien and Krylov system, respectively). Lavas from all three seamount groups, however, show geochemical evidence for involvement of enriched (Canary/Cape Verde) plume material. Seismic tomography shows that large areas around these mantle plumes are affected by dispersal of presumably low‐velocity material, which also could have fed nearby isolated seamounts with diffusely‐upwelling plume material. This process may be extremely widespread but has been poorly studied to date.

Description: Highlights • We present three geophysical profiles along the southern Chatham Rise margin. • Structural variations relate to Hikurangi Plateau collision and Zealandia rifting. • SE Chatham Terrace represents a broad COT (thin and modified continental crust). • The southern Chatham Rise margin is a unique hybrid-rifted margin. • Initial rifting was passive, but upwelling mantle affected the Chatham Rise margin. Abstract Passive continental margins are commonly classified as magma-poor and magma-rich types. Related breakup processes are often associated with far-field tectonic stresses or upwelling mantle plumes. The Chatham Rise east off New Zealand records a sequence of Late Cretaceous tectonic events, which include subduction and collision of the oceanic Hikurangi Plateau to subsequent continental rifting and breakup. The mechanisms triggering the change in tectonic forces are poorly understood but address open questions regarding the formation of passive margins. We acquired wide-angle seismic reflection/refraction, multi-channel seismic and potential field data along three profiles crossing the southern Chatham Rise margin and SE Chatham Terrace to the oceanic crust in order to image and understand the crustal structure and breakup mechanisms. Variations in crustal thickness along the highly faulted Chatham Rise are most likely related to the collision with the Hikurangi Plateau. Our data indicate that the SE Chatham Terrace represents a broad continent-ocean transition zone (COTZ), which we interpret to consist of very thin continental crust affected by magmatic activity. Along the southern Chatham Rise margin, features of both, magma-poor and magma-rich rifted margins are present. We suggest that passive rifting initiated at 105–100 Ma related to slab dynamics after the Hikurangi Plateau collision. We revise the onset of seafloor spreading south of the eastern Chatham Rise to ~88 Ma from the extent of our inferred COTZ. Geographically extensive, but low-volume intraplate magmatism affected the margin at 85–79 Ma. We suggest that this magmatism and the onset of seafloor spreading are a response to upwelling mantle through a slab window after 90 Ma. After 85 Ma, spreading segments became connected leading to the final separation of Zealandia from Antarctica. We interpret the southern Chatham Rise margin as a unique hybrid margin whose tectonic history was influenced by passive continental rifting and mantle upwelling.

Description: Highlights • Lithospheric mantle stabilization under Jiao-Liao-Ji Belt at 2.8Ga (SmNd isochron) • Liaohe mafic meta-igneous rocks formed in active continental margin subduction zone • Emplacement of Liaohe mafic igneous rocks at ~2.2 Ga (LuHf isochron) • Amphibolite retrograde metamorphism from exhumation at 1824 ± 19 Ma (PbPb isochron) • Cooling of terrane to ~500 °C at 1671 ± 58 Ma (RbSr isochron) Abstract The assembly and long-term evolution of the Eastern Block of the North China Craton are poorly constrained. Here we use bulk rock geochronological and geochemical data from mafic meta-igneous rocks (hornblendites, amphibolites and a metagabbro) of the Liaohe Group to reconstruct the Neoarchean to Paleoproterozoic history of the Jiao-Liao-Ji Belt, located between the Longgang and Nangrim blocks that together form the Eastern Block of the North China Craton. The mafic/ultramafic meta-igneous rocks have intrusive or tectonic contacts with the Liaoji granitic rocks (~2.2–2.0 Ga), which form the basement of the Jiao-Liao-Ji Belt. The major and trace element data indicate that the protoliths had calc-alkaline composition and formed along an active continental margin subduction zone. The mafic rocks form a whole-rock 176Lu/177Hf isochron with an age of 2.25 ± 0.31 Ga, overlapping with UPb zircon ages for mafic and granitic rocks from the Jiao-Liao-Ji Belt and consistent with being the emplacement age of the mafic protoliths along the active continental margin. In contrast, the whole-rock 147Sm/144Nd isochron age of 2.83 ± 0.18 Ga is likely to reflect the average age of the lithospheric mantle source from which the mafic/ultramafic protoliths were extracted. Together with geological evidence, we propose that the southwestern portion of the Longgang Block was an active continental margin since at least the early Paleoproteorozic. Literature age data from metamorphic zircons show that peak granulite metamorphism took place at ~1.96–1.88 Ga, resulting from the collisional event that fused the Longgang and Nangrim blocks into the Eastern Block of the North China Craton. Our bulk-rock 207Pb/206Pb age of 1824 ± 19 Ma and our 87Rb/86Sr age of 1671 ± 58 Ma reflect retrograde (cooling) stages during the exhumation of the Jiao-Liao-Ji Belt after the orogenesis.

Description: Age-progressive volcanism is generally accepted as the surface expression of deep-rooted mantle plumes, which are enigmatically linked with the African and Pacific large low-shear velocity provinces (LLSVPs). We present geochemical and geochronological data collected from the oldest portions of the age-progressive enriched mantle one (EMI)-type Tristan-Gough track. They are part of a 30- to 40-million year younger age-progressive hotspot track with St. Helena HIMU (high time-integrated U-238/Pb-204) composition, which is also observed at the EMI-type Shona hotspot track in the southernmost Atlantic. Whereas the primary EMI-type hotspots overlie the margin of the African LLSVP, the HIMU-type hotspots are located above a central portion of the African LLSVP, reflecting a large-scale geochemical zonation. We propose that extraction of large volumes of EMI-type mantle from the margin of the LLSVP by primary plume heads triggered upwelling of HIMU material from a more internal domain of the LLSVP, forming secondary plumes.

Description: Highlights • High-Ti lavas have the same composition as Walvis Ridge and Gough Subtrack. • Low-Ti lavas are derived from a distinct source compare to the high-Ti lavas. • High-Ti and low-Ti basalts reflect the spatial zonation of the plume head. • Tristan-type composition has not been discovered in the plume head stage. • Sr-Nd-Pb-Hf isotopes from Etendeka flood basalts. Abstract The origin and distribution of geochemically distinct source components in continental flood volcanism (generally associated with the initial phase of a mantle plume head) are poorly understood. Here we present new geochemical (major and trace element and Sr-Nd-Pb-Hf isotope) data from the Etendeka flood basalts and associated dikes from northern and central Namibia that are believed to have been produced during the initial stage of the Tristan-Gough hotspot. Following earlier studies, the Etendeka lava flows and dikes are divided into high-Ti and low-Ti groups. The trace element and isotopic composition of the high-Ti tholeiitic basalts, exclusively outcropping in northern Etendeka (northwestern Namibia), are similar to the Gough-type enriched mantle I (EMI) composition found on the Walvis Ridge (the Atlantic type locality for the EMI end member). The low-Ti tholeiitic basalts, primarily outcropping in Southern Etendeka (central western Namibia), have higher 143Nd/144Nd and 207Pb/204Pb but lower 208Pb/204Pb ratios than the Gough composition. Combining our data with newly published 3He/4He data and estimates of the magma source’s potential temperature from 1520-1680◦C, we conclude that the source of the low-Ti basalts was also intrinsic to the Tristan-Gough plume, consistent with a spatially-zoned plume head. The low-Ti basalts were derived from a distinct EMI-type source component that has thus far only been detected in the initial Tristan-Gough plume head (∼132 Ma), but not the later submarine hotspot track.

Description: Highlights • Common HIMU end member in adjacent continental and oceanic volcanic provinces. • End member St. Helena HIMU derived from deep upwelling(s)/plume(s). • Plateau collision & plume interaction with Gondwana active margin causes breakup. • Hybrid volcanic-tectonic margins resulted from Zealandia – Antarctica breakup. Abstract Margins resulting from continental breakup are generally classified as volcanic (related to flood basalt volcanism from a starting plume head) or non-volcanic (caused by tectonic processes), but many margins (breakups) may actually be hybrids caused by a combination of volcanic and tectonic processes. It has been postulated that the collision of the Hikurangi Plateau with the Gondwana margin ∼110 Ma ago caused subduction to cease, followed by large-scale extension and ultimately breakoff of the Zealandia micro-continent from West Antarctica through seafloor spreading which started at ∼85 Ma. Here we report new geochemical (major and trace element and Sr-Nd-Pb-Hf isotope) data for Late Cretaceous (99-69 Ma) volcanism from Zealandia, which include the calc-alkalic, subduction-related Mount Somers (99-96 Ma) and four intraplate igneous provinces: 1) Hikurangi Seamount Province (99-88 Ma), 2) Marlborough Igneous Province (98-94 Ma), 3) Westland Igneous Province (92-69 Ma), and 4) Eastern Chatham Igneous Province (86-79 Ma). Each of the intraplate provinces forms mixing arrays on incompatible-element and isotope ratio plots between HIMU (requiring long-term high U/204Pb) and either a depleted (MORB-source) upper mantle (DM) component or enriched continental (EM) type component (located in the crust and/or upper mantle) or a mixture of both. St. Helena end member HIMU could be the common component in all four provinces. Considering the uniformity in composition of the HIMU end member despite the type of lithosphere (continental, oceanic, oceanic plateau) beneath the igneous provinces, we attribute this component to a sublithospheric source, located beneath all volcanic provinces, and thus most likely a mantle plume. We propose that the plume material rose beneath the active Gondwana margin and flowed along the subducting lithosphere beneath the Hikurangi Plateau and neighboring seafloor and through slab tears/windows beneath the Gondwana (later to become Zealandia) continental lithosphere. We conclude that both plateau collision, resulting in subduction cessation, and the opening of slab tears/windows, allowing hot asthenosphere and/or plume material to upwell to shallow depths, were important in causing the breakup of Zealandia from West Antarctica. Combined tectonic-volcanic processes are also likely to be responsible for causing breakup and the formation of other hybrid type margins.

Description: Unlike the well-studied narrow hotspot tracks, the origin of broadly distributed seamount provinces remains a topic of conjecture. Here we present major and trace element and Sr-Nd-Hf-Pb double spike isotope data of a comprehensive sample suite from the Bathymetrists Seamount Province, a broad belt of submarine volcanoes in the eastern equatorial Atlantic, and from the neighboring Cape Verde Ridge, a topographic high on the shoulder of a local fracture zone. The major and trace element results are consistent with the Bathymetrists Seamount Province having formed in an intraplate setting. The isotopic composition of the seamount lavas resemble a HIMU-like signature (206Pb/204Pbin = 19.23–20.35) similar to the nearby St. Helena hotspot composition. Based on plate tectonic reconstructions, a formation of the Bathymetrists Seamount Province by the postulated Sierra Leone plume, believed to be responsible for the geochemical anomaly at the mid ocean ridge at 1.7°N and the nearby St. Peter and Pauls rocks, is not supported. An alternative model that the Bathymetrists Seamount Province was created by edge driven convection in the upper mantle along the boundary of the neighboring Sierra Leone Rise plateau is also not supported by the available data. Plate tectonic reconstructions, however, are consistent with a hotspot origin for the Bathymetrists Seamount Province, as is the presence of a seismic tomographic anomaly at the southwest end of the seamount belt.

Description: Highlights • New trace element and Sr-Nd-Pb isotope data for SVZ crustal and trench sediment samples. • New whole-rock Hf–O isotope data for crustal and trench sediment samples. • Nd model ages confirm a Mesoproterozoic crustal residence age for the Guarguaráz complex. • NSVZ trench sediments reflect the source composition of eroded mafic material. Abstract This paper provides new trace element and Sr-Nd-Hf-Pb-O isotope data on Neoproterozoic to Phanerozoic mid to upper crustal lithologies of the Andean basement in central Chile and western Argentina (33°-35°S; 69°-72°W). It also provides additional data on trench sediments being subducted offshore the northern segment of the Southern Volcanic Zone in Chile. Neoproterozoic metamorphic and igneous rocks from the Guarguaráz complex (Argentina; 33.6°S, 69.5°W), when back corrected to 350 Ma, display a narrow range in 87Sr/86Sri (0.713–0.718), 143Nd/144Ndi (0.5118–0.5121), εNdi (−8.1 to −1.1), εHfi (−11.4 to +1.2) and δ18O (9–13‰). Nd model ages (TDM = 1.08–1.65 Ga) for the Guarguaráz complex points to a Mesoproterozoic crustal residence age for these rocks. Metasedimentary rocks from the Carboniferous accretionary prism in central Chile (~34°S) overlap with these ranges, but differ by having lower initial 87Sr/86Sri (0.7052–0.7093) and higher δ18O (14–17‰). The Guarguaráz metamorphic and igneous rocks, when back corrected to 350 Ma, have similar Pb isotope ratios than the Chilean Carboniferous metasedimentary rocks (206Pb/204Pbi = 17.58–18.52 vs. 18.33–18.46; 207Pb/204Pbi = 15.50–15.64 vs. ~15.64; 208Pb/204Pbi = 37.70–38.36 vs. 37.98–38.18). Two Guarguaráz samples are shifted towards less radiogenic Pb isotope ratios, similar to samples representative of the Cuyania basement. This suggests that Chilenia hosts at least two geochemical components: (1) a component with unradiogenic Pb isotopes, similar to the Proterozoic Cuyania basement, and (2) a component with more radiogenic Pb isotopes, similar to Chilean Phanerozoic metasedimentary and igneous rocks. The ranges in Pb isotope ratios for the Chilean Mesozoic (206Pb/204Pbi = 18.44–19.86; 207Pb/204Pbi = 15.59–15.69; 208Pb/204Pbi = 38.30–40.30) and Miocene (206Pb/204Pbi = 18.43–18.57; 207Pb/204Pbi = 15.58–15.60; 208Pb/204Pbi = 38.33–38.46) igneous rocks are similar to those of the accretionary prism. The Mesozoic and Miocene intrusive rocks are characterized by low 87Sr/86Sri (0.704–0.708 and ~0.704, respectively) and high εNdi (−6.2 to +4.0 and + 3.9 to +5.9, respectively) and εHfi (+7.0 to +12.7 and + 8.5 to +10.8, respectively). They can be divided into two groups. Group (1), consisting exclusively of Mesozoic samples, has negative εNdi, 87Sr/86Sri 〉 0.706, elevated e.g., Ba/Th, Nb/Yb, Zr/Y and lower Nb/La, reflecting derivation from enriched (most likely overriding crust or mantle) material. Group (2), consisting of Mesozoic and Miocene rocks, has positive εNdi, εHfi, and lower initial 87Sr/86Sri than group (1) reflecting depleted mantle melts addition to the crust. Finally, Sr-Nd-O isotopic compositions of the trench sediments at latitude 33°-33.3°S are almost identical to those at latitude 35°-40°S, indicating a relative homogeneous material input along the SVZ, although there are subtle differences in REE and Pb isotopic compositions. Based on Nd–Hf isotopes, trench sediments offshore Chile (εNd〉 +1; εHf 〉 +2) and offshore Peru (εNd 〈 −2; εHf 〈 +1) have distinct compositions, reflecting the differences in input material. The positive εNd and εHf values suggest derivation from eroded depleted mantle-derived mafic material.