The Tristan-Gough-Walvis Ridge volcanic chain, located in the South Atlantic Ocean on the African plate, is one of Earth's longest linear seafloor features. However, the origin of its magmatism remains poorly understood. To better understand its formation, temporal evolution, and geochemical characteristics, six sites were drilled along the Tristan-Gough-Walvis Ridge chain by International Ocean Discovery Program (IODP) Expeditions 391 and 397T: three sites on Valdivia Bank (U1575, U1576, and U1577) and three sites in the Guyot Province (U1578, U1584, and U1585). Among these, Site U1578, located on the deep northwestern flank of a "Center track" seamount, represents the deepest basement penetration (>300 m) of both expeditions. According to preliminary geophysical and biostratigraphic constraints, the stratigraphic sections recovered from Site U1578 span >2.0 m.y. of the Paleocene (ca. 64.8-62.3 Ma). Here, we present an integrated study of major and trace element concentrations in minerals, combined with in situ Sr isotopes of plagioclase (Pl) from Site U1578 basalts. Based on the olivine-spinel (Ol-Sp) thermometry and pyMelt modeling, the calculated mantle potential temperature of the Center track is >= 1400 degrees C, which is similar to 50 degrees C higher than that of mid-ocean-ridge basalts (MORBs), most likely reflecting the influence of a mantle plume. Based on geochemical compositions and crystal textures, we identified three distinct clinopyroxene (Cpx) groups: Group 1 is characterized by high Mg# (>83.4) and elevated Ni (>200 ppm) and Cr (>5000 ppm) contents; Group 2 has intermediate Mg# (76.6-83.4), Ni (100-200 ppm), and Cr (1000-5000 ppm); and Group 3 exhibits low Mg# (<76.6) and depleted Ni (<70 ppm) and Cr (<30 ppm) contents. Multiple episodes of magma recharge and mixing in the plumbing system beneath the Center track produced a diversity of mineral textures, including normal, reverse, sector, and oscillatory zoning. Additionally, Pl from this site is isotopically heterogeneous (Sr-87/Sr-86 of 0.7038 +/- 0.0001 to 0.7046 +/- 0.0001) and broadly similar to basalts from the northern Tristan track in the Guyot Province. A shift to more radiogenic Sr isotopic signatures from the lower to the upper igneous units suggests the increasing incorporation of radiogenic materials into the mantle source with time, potentially derived from enriched mantle typically associated with basalts of the southern Gough track. These findings indicate that basaltic lavas from the Center track originate from an anomalously hot and geochemically enriched mantle source associated with a mantle plume or hotspot activity. Diverse mineral textures and chemistry record complex fractional crystallization and mixing processes during magma storage prior to eruption.

Recent changes in US oceanographic assets are impacting scientists' ability to access seafloor and sub‐seafloor materials and thus constraining progress on science critical for societal needs. Here we identify national infrastructure needs to address critical science questions. This commentary reports on community‐driven discussions that took place during the 3‐day FUTURE of US Seafloor Sampling Capabilities 2024 Workshop , which used an “all‐hands‐on‐deck” approach to assess seafloor and sub‐seafloor sampling requirements of a broad range of scientific objectives, focusing on capabilities that could be supported through the US Academic Research Fleet (US‐ARF) now or in the near future. Cross‐cutting issues identified included weight and size limitations in the over‐boarding capabilities of the US‐ARF, a need to access material at depths greater than ∼20 m below the seafloor, sampling capabilities at the full range of ocean depths, technologies required for precise navigation‐guided sampling and drilling, resources to capitalize on the research potential of returned materials, and workforce development.

The Rio Grande Rise (RGR) oceanic plateau exhibits distinctly broad morphology compared to the linear, age-progressive Walvis Ridge (WR), despite both originating from the Tristan-Gough (T-G) plume. New 40Ar/39Ar ages (84-41 Ma) from RGR demonstrate prolonged coeval formation with WR at the Mid-Atlantic Ridge (MAR) during a ridge-centered plume configuration. These plume-ridge interactions coincided with a temporary microplate eventually incorporated into the South American Plate, explaining RGR's broader spatial distribution. Backtracking reveals that absolute plate motion and southward plume drift shut off excess magma supply when the T-G plume moved south of large lateral MAR offsets, ending volcanism on the South American plate around 52 Ma-later than previously estimated. Although RGR's erupted volume matches large igneous provinces, magmatic production rates were moderate, resembling modern-day Iceland rather than high-flux terrestrial large igneous provinces. This supports a ridge-centered plume origin over a high-flux magma pulse, demonstrating how plume-ridge configuration and microplate tectonics controlled the evolutionary divergence of these related South Atlantic volcanic features.

Massive submarine basalt flows were sampled at five sites on the Tristan-Gough-Walvis hotspot track in the South Atlantic by International Oceanic Discovery Program Expeditions 391/397T, where the plume was interacting with a mid-ocean ridge, a setting similar to that the of modern Iceland. High resolution XRF core scans document significant internal chemical variations with depth in these flows. Some of this reflects basal olivine accumulation. However, some examples have "scallop-shaped" patterns that are interpreted to represent influxes of new magma during flow lobe inflation with successive lava injections focused toward the base of the flow unit. Olivine concentration in the deeper parts of the flow is interpreted to reflect top-down tapping of a vertically zoned magma chamber, with the upper part of the chamber erupting first, and successive eruptive pulses tapping progressively deeper levels of the stratified chamber. The occurrence of massive submarine lava flows requires high eruptive fluxes relative to pillow lava formation. Propagation of these massive flows is favored by (a) high sea water confining pressures, which inhibit vesiculation and keep effective viscosity low and dissolved volatile content high, and (b) chill zones and thick viscoelastic crusts of quenched lava on the flow tops, which effectively insulate the flow interior from ambient temperatures. The formation of a thin film of super-heated steam on the upper flow surface may similarly enhance the insulation. Evidence suggests that similar massive flows on the seafloor may extend many kilometers from their vents.

The western margin of the Arabian Shield along the Red Sea between Jordan and Yemen is littered with numerous (mostly mid-Miocene to Quaternary) basalt fields known as harrats. Harrat Uwayrid consists of a NW-SE-oriented elongated field that extends for c. 230 km in NW Saudi Arabia. The magmatic activities include older alkaline lava flows of transitional basalt, alkali basalt, hawaiite and basanite, together with younger scoria basanite that erupted through the central segment of the older lavas. Based on chondrite-normalized Sm/Yb v. La/Yb and Tb/Yb v. La/Sm diagrams, we show that the older transitional lavas were generated from spinel lherzolite, whereas the younger lavas were generated from garnet lherzolite. The primitive-mantle-normalized patterns are similar to those of ocean island basalts. Ar-40/Ar-39 plateau dating yields eruption ages of 10.15 +/- 0.09 to 9.87 +/- 0.04 Ma (n = 3) for the older alkaline basalts and 0.96 +/- 0.03 to 0.16 +/- 0.03 Ma (n = 5) for the younger basanites. The Nd-143/Nd-144 ratios for both the older lavas and the younger scoria are 0.51285-0.51292 and epsilon(Nd) (4.0-5.4) is positive; the ratios of Sr-87/Sr-86 are low (0.7032-0.7039). The range of Pb-206/Pb-204 (18.5305-19.3701) values and the Nd-143/Nd-144 v. Sr-87/Sr-86 ratios overlap those of FOcal ZOne (FOZO)-type mantle; we interpret this FOZO signature to indicate metasomatism of the asthenosphere from slabs subducted during the construction of the 900-550 Ma Arabian-Nubian Shield. Harrat Uwayrid records (possibly plume-related) potential temperatures of 1400-1490 degrees C and pressures of 2.0-4.4 GPa (c. 70-140 km depth), which are within the range of the Afar plume. Some Harrat Uwayrid scoria and lava also fall within the isotopic range of basalts in the Red Sea trough, Yemini flood basalts and Afar plume basalts. After the collision of Arabia-Eurasia in the Miocene, the subsequent eastern movement of the Arabian Shield caused asymmetrical drag of the upwelling asthenosphere (and possibly also the Afar plume) and the magma chambers to a location beneath the western limb of the Arabian Shield.

Maunaloa-the largest active volcano on Earth-erupted in 2022 after its longest known repose period (similar to 38 years) and two decades of volcanic unrest. This eruptive hiatus at Maunaloa encompasses most of the similar to 35-year-long Pu'u'o'o eruption of neighboring Kilauea, which ended in 2018 with a collapse of the summit caldera and an unusually voluminous (similar to 1 km(3)) rift eruption. A long-term pattern of such anticorrelated eruptive behavior suggests that a magmatic connection exists between these volcanoes within the asthenospheric mantle source and melting region, the lithospheric mantle, and/or the volcanic edifice. The exact nature of this connection is enigmatic. In the past, the distinct compositions of lavas from Kilauea and Maunaloa were thought to require completely separate magma pathways from the mantle source of each volcano to the surface. Here, we use a nearly 200-yr record of lava chemistry from both volcanoes to demonstrate that melt from a shared mantle source within the Hawaiian plume may be transported alternately to Kilauea or Maunaloa on a timescale of decades. This process led to a correlated temporal variation in Pb-206/Pb-204 and Sr-87/Sr-86 at these volcanoes since the early 19th century with each becoming more active when it received melt from the shared source. Ratios of highly over moderately incompatible trace elements (e.g. Nb/Y) at Kilauea reached a minimum from similar to 2000 to 2010, which coincides with an increase in seismicity and inflation at the summit of Maunaloa. Thereafter, a reversal in Nb/Y at Kilauea signals a decline in the degree of mantle partial melting at this volcano and suggests that melt from the shared source is now being diverted from Kilauea to Maunaloa for the first time since the early to mid-20th century. These observations link a mantle-related shift in melt generation and transport at Kilauea to the awakening of Maunaloa in 2002 and its eruption in 2022. Monitoring of lava chemistry is a potential tool that may be used to forecast the behavior (e.g. eruption rate and frequency) of these adjacent volcanoes on a timescale of decades. A future increase in eruptive activity at Maunaloa is likely if the temporal increase in Nb/Y continues at Kilauea.

The past similar to 200 million years of Earth's geomagnetic field behavior have been recorded within oceanic basalts, many of which are only accessible via scientific ocean drilling. Obtaining the best possible paleomagnetic measurements from such valuable samples requires an a priori understanding of their magnetic mineralogies when choosing the most appropriate protocol for stepwise demagnetization experiments (either alternating field or thermal). Here, we present a quick, and non-destructive method that utilizes the amplitude-dependence of magnetic susceptibility to screen submarine basalts prior to choosing a demagnetization protocol, whenever conducting a pilot study or other detailed rock-magnetic characterization is not possible. We demonstrate this method using samples acquired during International Ocean Discovery Program Expedition 391. Our approach is rooted in the observation that amplitude-dependent magnetic susceptibility is observed in basalt samples whose dominant magnetic carrier is multidomain titanomagnetite (similar to TM60-65, (Ti0.60-0.65Fe0.35-0.40)Fe2O4). Samples with low Ti contents within titanomagnetite or samples that have experienced a high degree of oxidative weathering do not display appreciable amplitude dependence. Due to their low Curie temperatures, basalts that possess amplitude-dependence should ideally be demagnetized either using alternating fields or via finely-spaced thermal demagnetization heating steps below 300 degrees C. Our screening method can enhance the success rate of paleomagnetic studies of oceanic basalt samples. Oceanic basalts are ideal recorders of the Earth's magnetic field. To decipher magnetic histories recorded in rocks, paleomagnetists need to isolate the magnetization directions and intensities within rocks by one of two possible methods. One method typically involves progressively heating the samples to high temperatures. The other method involves exposing samples to alternating magnetic fields with increasing peak field intensities. Both of these methods are ultimately destructive to the original magnetization preserved within rocks. However, without knowledge of a given rock's magnetic mineralogy, randomly choosing thermal or alternating field demagnetization methods may result in high failure rates. We developed a pre-screening method to help decide which cleaning method will likely be more successful for a given sample based on low-field magnetic susceptibility measurements. These measurements do not affect the original magnetic information recorded in a rock, thereby permitting subsequent paleomagnetic studies on the same sample. Our technique can be performed as rapidly as 2 min per sample, is non-destructive, and does not require complicated sample preparation. Paleomagnetic studies utilize either alternating field or thermal demagnetization, but it is difficult to choose the best protocol a priori Amplitude-dependence of magnetic susceptibility measurements permits preliminary magnetic mineralogy characterization in submarine basalts Rapid amplitude-dependence measurements may aid in deciding upon the best demagnetization protocol for submarine basalt samples

The Easter mantle plume has produced one of the longest hotspot tracks in the Pacific Ocean. While previous studies have focused on the eastern side extending across the Nazca Plate, we use 40Ar/39Ar isotopic and geochemical data to investigate the less explored western side around the Easter Microplate. We propose a dynamic model in which a deeper (600 km-depth), less buoyant mantle exerts a westward force on the East Pacific Rise (EPR), while a more buoyant plume region drives Easter hotspot volcanism and a localised acceleration in seafloor spreading. Our findings suggest that the Easter hotspot is the more focused surface expression of the most buoyant region of a vast, deep-seated mantle plume extending from the Pacific Large Low Shear Velocity Province (LLSVP). This challenges the traditional view of hotspots as isolated phenomena and suggests they are part of broader LLSVP-related mantle structures. Our results imply a more intricate, large-scale relationship between hotspots, mantle plumes, spreading ridges, and mantle dynamics. Examination of the Easter hotspot reveals it as part of a vast, deep-seated mantle system, influencing seafloor spreading and shaping the Pacific Ocean, which challenges the view of hotspots as isolated volcanic centres.

Images of the outside of hard rock whole-round sections were acquired using a linescan imager (Section Half Imaging Logger [SHIL]) and a special holder that allows each 90 degree segment of the outer surface to be positioned properly. The images were taken at a resolution of 20 lines/mm (50 micropixels). JRSO staff take these quadrant images and compile them into a side-by-side rollout photograph of the section. Composite images are available as both JPG and TIF image formats. Individual quadrant images are available as JPG images only through this report; contact the IODP-JRSO Data Librarian if quadrant TIF files (~160 MB) are needed.

Abstract Valdivia Bank (VB) is a Late Cretaceous oceanic plateau formed by volcanism from the Tristan‐Gough hotspot at the Mid‐Atlantic Ridge (MAR). To better understand its origin and evolution, magnetic data were used to generate a magnetic anomaly grid, which was inverted to determine crustal magnetization. The magnetization model reveals quasi‐linear polarity zones crossing the plateau and following expected MAR paleo‐locations, implying formation by seafloor spreading over ∼4 Myr during the formation of anomalies C34n‐C33r. Paleomagnetism and biostratigraphy data from International Ocean Discovery Program Expedition 391 confirm the magnetic interpretation. Anomaly C33r is split into two negative bands, likely by a westward ridge jump. One of these negative anomalies coincides with deep rift valleys, indicating their age and mechanism of formation. These findings imply that VB originated by seafloor spreading‐type volcanism during a plate reorganization, not from a vertical stack of lava flows as expected for a large volcano.

Magnetic susceptibility was measured on whole-round sections (and rarely section halves) on the Whole-Round Multisensor Logger (WRMSL) and/or Special Task Multisensor Logger (STMSL) using a Bartington MS2 meter and a 90 mm or 80 mm MS2C loop. As volume of the sample is not controlled for this experiment, susceptibility units are recorded in instrument units and are not volume-corrected.

Operational rig information data were measured using a variety of sensors and compiled using the RigWatch software package. Approximately 50 channels of drilling/coring data are captured in real time during the expedition. Data are presented as ASCII files extracted from the proprietary RigWatch data files and are presented by expedition. RigWatch data in time or depth domain can be imported into graphics and analysis programs to be merged and correlated with core physical properties data to enhance assessment of poor core recovery intervals.