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1. The origin of the Musicians Seamount Province and its inferences for Late Cretaceous Pacific Plate Motion

   https://doi.org/10.1016/j.margeo.2023.107166  

   Balbas, Andrea; Jung, Carl; Konrad, Kevin (November 2023, Marine Geology)

   Linear chains of seamounts, sourced from mantle plume processes, have the potential to refine plate motion models because the hotspot remains fixed relative to the moving lithospheric plate. However, to define plate motion, consistent seamount age progression and geometry are required. Some seamount chains, such as the Musician Seamount Province (MSP), have complex geometries and age distributions, which complicates calibrating plate motion. The MSP resides northwest of the Hawaiian Islands and is composed of seamounts and volcanic elongated ridges (VERs) that cover ∼420,000 km2 of Pacific seafloor. Here we provide new 40Ar/39Ar age determinations for a series of lava flows recovered from the MSP during expedition EX1708 of the National Oceanic and Atmospheric Administration's Ocean Exploration program. The MSP was built by four distinct volcanic processes: (1) age-progressive hotspot volcanism associated with the Euterpe Plume (ca. 98–79 Ma). (2) VER formation from plume-ridge channelization (ca. 97–94 Ma; 86–79 Ma) where the VERs only form when the hotspot is within ∼600 km of the ridge. (3) Eocene volcanism driven by extension during the ca. 50 Ma change in Pacific rotation poles (ca. 54–47 Ma). (4) Some near-ridge shear-driven upwelling or diffuse extensional volcanism that preceded the southern MSP lithosphere overriding the plume (ca. 86–84 Ma). By filtering lava flows with only robust statistically concordant 40Ar/39Ar age determinations as well as geologic setting, we develop a dataset of samples valuable for constraining Pacific plate motion. A local plate velocity of 42 ± 9 km/Ma for the 98–81 Ma time frame is calculated. Furthermore, the seamount track indicates that large shifts in Pacific rotation pole locations are required prior to 98 Ma and at ca. 81 Ma. 

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2. “Missing links” for the long-lived Macdonald and Aragohotspots, South Pacific Ocean

   https://doi.org/10.1130/G48276.1  

   Buff, L.; Jackson, M.G.; Konrad, K.; Konter, J.G.; Bizimis, M.; Price, A.; Rose-Koga, E.F.; Blusztajn, J.; Koppers, A.A.P.; Herrera, Santiago (January 2021, Geology)

   null (Ed.)

   The Cook-Austral volcanic lineament extends from Macdonald Seamount (east) to Aitutaki Island (west) in the South Pacific Ocean and consists of hotspot-related volcanic islands, seamounts, and atolls. The Cook-Austral volcanic lineament has been characterized as multiple overlapping, age-progressive hotspot tracks generated by at least two mantle plumes, including the Arago and Macdonald plumes, which have fed volcano construction for ~20 m.y. The Arago and Macdonald hotspot tracks are argued to have been active for at least 70 m.y. and to extend northwest of the Cook-Austral volcanic lineament into the Cretaceous-aged Tuvalu-Gilbert and Tokelau Island chains, respectively. Large gaps in sampling exist along the predicted hotspot tracks, complicating efforts seeking to show that the Arago and Macdonald hotspots have been continuous, long-lived sources of hotspot volcanism back into the Cretaceous. We present new major- and trace-element concentrations and radiogenic isotopes for three seamounts (Moki, Malulu, Dino) and one atoll (Rose), and new clinopyroxene 40Ar/39Ar ages for Rose (24.81 ± 1.02 Ma) and Moki (44.53 ± 10.05 Ma). All volcanoes are located in the poorly sampled region between the younger Cook-Austral and the older, Cretaceous portions of the Arago and Macdonald hotspot tracks. Absolute plate motion modeling indicates that the Rose and Moki volcanoes lie on or near the reconstructed traces of the Arago and Macdonald hotspots, respectively, and the 40Ar/39Ar ages for Rose and Moki align with the predicted age progression for the Arago (Rose) and Macdonald (Moki) hotspots, thereby linking the younger Cook-Austral and older Cretaceous portions of the long-lived (>70 m.y.) Arago and Macdonald hotspot tracks. 

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3. Challenger Deep basalts reveal Indian-type Early Cretaceous oceanic crust subducting in the southernmost Mariana Trench

   Xu, W; Peng, X; Stern, R; Xu, X; Xu, H (July 2023, Geology)

   Why the Challenger Deep, the deepest point on Earth’s solid surface, is so deep is unclear, but part of the reason must be the age and density of the downgoing plate. Northwest Pacific oceanic crust subducting in the Izu-Bonin-Mariana Trench is Cretaceous and Jurassic, but the age and nature of Pacific oceanic crust subducting in the southernmost Mariana Trench remains unknown. Here we present the first study of seafloor basalts recovered by the full-ocean-depth crewed submersible Fendouzhe from the deepest seafloor around the Challenger Deep, from both the overriding and downgoing plates. 40Ar/39Ar ages indicate that downgo¬ing basalts are Early Cretaceous (ca. 125 Ma), indicating they are part of the Pacific plate rather than the nearby Oligocene Caroline microplate. Downgoing-plate basalts are slightly enriched in incompatible elements but have similar trace element and Hf isotope compositions to other northwest Pacific mid-ocean ridge basalts (MORBs). They also have slightly enriched Sr-Nd-Pb isotope compositions like those of the Indian mantle domain. These features may have formed with contributions from plume-derived components via plume-ridge interac¬tions. One sample from the overriding plate gives an 40Ar/39Ar age of ca. 55 Ma, about the same age as subduction initiation, to form the Izu-Bonin-Mariana convergent margin. Our results suggest that 50%–90% of the Pb budget of Mariana arc magmas is derived from the subducted MORBs with Indian-type isotope affinity. 

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4. The multiple depleted mantle components in the Hawaiian-Emperor chain

   https://doi.org/10.1016/j.chemgeo.2019.119324  

   Harrison, L; Weis, D; Garcia, M.O. (January 2020, Chemical geology)

   null (Ed.)

   Oceanic island basalts are targeted for geochemical study because they provide a direct window into mantle composition and a wealth of information on the dynamics and timescales associated with Earth mixing. Previous studies mainly focused on the shield volcanic stage of oceanic islands and the more fusible, enriched mantle components that are easily distinguished in those basalts. Mantle depleted compositions are typically more difficult to resolve unless large amounts of this material participated in mantle melting (e.g., mid-ocean ridges), or unique processes allow for their compositions to be erupted undiluted, such as very small degrees of melting of a source with minimal fusible enriched components (e.g., rejuvenated basalts) or as xenoliths (e.g., abyssal peridotites). Mantle depleted components, defined here as material with low time-integrated Rb/Sr (low 87Sr/86Sr) and high time-integrated Sm/Nd and Lu/Hf ratios (high 143Nd/144Nd and 176Hf/177Hf) relative to primitive mantle, derive from a potentially very large volume reservoir (up to 80% of the mantle), and therefore need adequate characterization in order estimate the composition of the Earth and mantle-derived melts. This review focuses on mantle depleted compositions in oceanic island basalts using the Hawaiian-Emperor chain as a case study. The Hawaiian-Emperor chain is the ∼6000 km long geological record of the deeply sourced Hawaiian mantle plume, active for>81 Myr. Hawaiian volcanism evolves through four volcanic stages as a volcano traverses the Hawaiian plume: alkalic preshield, tholeiitic shield (80–90% volcano volume), alkalic postshield (∼1%), and silica undersaturated rejuvenated (< 0.1%). We report Pb-Sr-Nd-Hf isotope compositions and trace element concentrations of three rejuvenated Northwest Hawaiian Ridge basalts and compare them to an exhaustive compiled dataset of basalts from the Hawaiian Islands to the Emperor Seamounts. The Northwest Hawaiian Ridge (NWHR) includes 51 volcanoes spanning ∼42 m.y. between the bend in the Hawaiian-Emperor chain and the Hawaiian Islands where there is no high-precision isotopic data published on the rejuvenated-stage over ∼47% of the chain. NWHR and Hawaiian Island rejuvenated basalts are geochemically similar, indicating a consistent source for rejuvenated volcanism over ∼12.5 million years. In contrast, shield-stage basalts from the oldest Emperor Seamounts are more depleted in isotopic composition (i.e., higher 176Hf/177Hf, and 143Nd/144Nd with lower 87Sr/86Sr and 208Pb*/206Pb*) and trace element concentrations (i.e., much lower concentrations of highly incompatible elements) than all other depleted Hawaiian basalts younger than the bend, including NWHR rejuvenated basalts. The strongly depleted source for the oldest Emperor Seamounts (> 70 Ma) was likely related to interaction with the Kula-Pacific-Izanagi mid-ocean ridge spreading system active near the Hawaiian plume in the Late Cretaceous. In contrast, the incompatible trace element ratios of NWHR rejuvenated basalts require a distinct source in the Hawaiian mantle plume that was imprinted by ancient (> 1 Ga) partial melting, likely ancient recycled oceanic lithosphere. This review of the geochemistry of Hawaiian depleted components documents the need for the sampling of multiple distinctive depleted compositions, each preferentially melted during specific periods of Hawaiian plume activity. This suggests that the composition of depleted components can evolve during the lifetime of the mantle plume, as observed for enriched components in the Hawaiian mantle plume. Changes in the composition of depleted components are dominantly controlled by the upper mantle tectonic configurations at the time of eruption (i.e., proximity to a mid-ocean ridge), as this effect overwhelms the signal imparted by potentially sampling different lower mantle components through time. 

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5. Relative Timing of Off‐Axis Volcanism From Sediment Thickness Estimates on the 8°20’N Seamount Chain, East Pacific Rise

   https://doi.org/10.1029/2022GC010335  

   Fabbrizzi, Andrea; Parnell‐Turner, Ross; Gregg, Patricia M.; Fornari, Daniel J.; Perfit, Michael R.; Wanless, V. Dorsey; Anderson, Molly (September 2022, Geochemistry, Geophysics, Geosystems)

   Abstract Volcanic seamount chains on the flanks of mid‐ocean ridges record variability in magmatic processes associated with mantle melting over several millions of years. However, the relative timing of magmatism on individual seamounts along a chain can be difficult to estimate withoutin situsampling and is further hampered by Ar⁴⁰/Ar³⁹dating limitations. The 8°20’N seamount chain extends ∼170 km west from the fast‐spreading East Pacific Rise (EPR), north of and parallel to the western Siqueiros fracture zone. Here, we use multibeam bathymetric data to investigate relationships between abyssal hill formation and seamount volcanism, transform fault slip, and tectonic rotation. Near‐bottom compressed high‐intensity radiated pulse, bathymetric, and sidescan sonar data collected with the autonomous underwater vehicleSentryare used to test the hypothesis that seamount volcanism is age‐progressive along the seamount chain. Although sediment on seamount flanks is likely to be reworked by gravitational mass‐wasting and current activity, bathymetric relief andSentryvehicle heading analysis suggest that sedimentary accumulations on seamount summits are likely to be relatively pristine. Sediment thickness on the seamounts' summits does not increase linearly with nominal crustal age, as would be predicted if seamounts were constructed proximal to the EPR axis and then aged as the lithosphere cooled and subsided away from the ridge. The thickest sediments are found at the center of the chain, implying the most ancient volcanism there, rather than on seamounts furthest from the EPR. The nonlinear sediment thickness along the 8°20’N seamounts suggests that volcanism can persist off‐axis for several million years. 

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