Age -progressive seamount tracks generated by lithospheric motion over a stationary mantle plume have long been used to reconstruct absolute plate motion (APM) models. However, the basis of these models requires the plumes to move significantly slower than the overriding lithosphere. When a plume interacts with a convergent or divergent plate boundary, it is often deflected within the strong local mantle flow fields associated with such regimes. Here, we examined the age progression and geometry of the Samoa hotspot track, focusing on lava flow samples dredged from the deep flanks of seamounts in order to best reconstruct when a given seamount was overlying the mantle plume (i.e., during the shield -building stage). The Samoan seamounts display an apparent local plate velocity of 7.8 cm/yr from 0 to 9 Ma, 11.1 cm/yr from 9 to 14 Ma, and 5.6 cm/yr from 14 to 24 Ma. Current fixed and mobile hotspot Pacific APM models cannot reproduce the geometry of the Samoa seamount track if a long-term fixed hotspot location, currently beneath the active Vailulu'u Seamount, is assumed. Rather, reconstruction of the eruptive locations of the Samoan seamounts using APM models indicates that the surface expression of the plume migrated similar to 2 degrees northward in the Pliocene. Large-scale mantle flow beneath the Pacific Ocean Basin cannot explain this plume migration. Instead, the best explanation is that toroidal flow fields-generated by westward migration of the Tonga Trench and associated slab rollback-have deflected the conduit northward over the past 2-3 m.y. These observations provide novel constraints on the ways in which plume -trench interactions can alter hotspot track geometries.

The ocean basins contain numerous volcanic ridges, seamounts and large igneous provinces (LIPs). Numerous studies have focused on the origin of seamount chains and LIPs but much less focus has been applied to understanding the genesis of large volcanic structures formed from a combination or series of volcanic drivers. Here we propose the term Oceanic Mid-plate Superstructures (OMS) to describe independent bathymetric swells or volcanic structures that are constructed through superimposing pulses of volcanism, over long time periods and from multiple sources. These sources can represent periods when the lithosphere drifted over different mantle plumes and/or experienced pulses of volcanism associated with shallow tectonic drivers (e.g. plate flexure; lithospheric extension). Here we focus on the Melanesian Border Plateau (MBP), one example of an OMS that has a complex and enigmatic origin. The MBP is a region of shallow Pacific lithosphere consisting of high volumes of volcanic guyots, ridges and seamounts that resides on the northern edge of the Vitiaz Lineament. Here we reconcile recently published constraints to build a comprehensive volcanic history of the MBP. The MBP was built through four distinct episodes: (1) Volcanism associated with the Louisville hotspot likely generating Robbie Ridge and some Cretaceous seamounts near the MBP. (2) Construction of oceanic islands and seamounts during the Eocene when the lithosphere passed over the Rurutu-Arago hotspot. (3) Reactivation of previous oceanic islands/seamounts and construction of new volcanos in the Miocene when the lithosphere passed over the Samoa hotspot. (4) Miocene to modern volcanism driven by lithospheric deformation and/or westward entrainment of enriched plume mantle due to toroidal mantle flow driven by the rollback of the Pacific plate beneath the Tonga trench. The combination of these processes is responsible for similar to 222,000 km(2) of intraplate volcanism in the MBP and indicates that this OMS was constructed from multiple volcanic drivers.

Abstract Breakup of the proposed greater Ontong Java Nui large igneous province during the Cretaceous Normal Superchron can be constrained by the opening of the Ellice Basin (EB) separating the Ontong Java and Manihiki Plateaus and the Osbourn Basin separating the Manihiki and Hikurangi Plateaus. Dating of recovered dredged samples using plagioclase 40Ar/39Ar and zircon U/Pb geochronology methods indicates that spreading was well underway in the EB by 118 Ma with full spreading rates up to 3X faster than any observed today of 30–45 cm/yr and spreading likely continued until 112‐108 Ma. Ellice Basin samples show diverse geochemical affinities ranging from mid‐ocean ridge basalt (MORB) or Ontong Java‐like to more enriched OIB‐like. Pb and Nd isotopes from six samples contain varying influences from Pacific MORB and possibly Ontong Java. The geochemistry shows a lack of a clear mantle plume influence despite EB's close temporal and spatial relationship to Ontong Java, while some data resemble the Louisville Seamounts. This compositional diversity complements morphological differences among dredge sites and shows that both in situ MORB and younger overprinted features related to the nearby Tuvalu Seamounts were sampled. 40Ar/39Ar geochronology confirms the age of International Ocean Discovery Program Site U1365 near the Osbourn Trough (OT) to be 102.60 ± 0.26 Ma (2σ, n = 18). This age constrains the timing of a spreading reorientation event observed in the OB to coincide with a global plate reorganization event around 105 Ma and estimates the cessation of spreading at the OT to 96 Ma.

The Northwestern Hawaiian Ridge is an age-progressive volcanic chain sourced from the Hawaiian mantle plume. Proximal to the Northwestern Hawaiian Ridge are several clusters of smaller seamounts and ridges with limited age constraints and unknown geodynamic origins. This study presents new bathymetric data and 40Ar/39Ar age determinations from lava flow samples recovered by remotely operated vehicle (ROV) from two east–west-trending chains of seamounts that lie north of the Pūhāhonu and Mokumanamana volcanoes. The previously unexplored Naifeh Chain (28°48′N,167°48′W) and Plumeria Chain (25°36′N, 164°35′W) contain five volcanic structures each, including three guyots in the Naifeh Chain. New 40Ar/39Ar age determinations indicate that the Naifeh Chain formed ca. 88 Ma and the Plumeria Chain ca. 85 Ma. The Cretaceous ages, coupled with a perpendicular orientation of the seamounts relative to absolute Pacific plate motion at that time, eliminate either a Miocene Hawaiian volcanic arch or Cretaceous mantle-plume origin. The seamounts lie on oceanic crust that is modeled to be 10–15 Ma older than the corresponding seamounts. Here, two models are put forth to explain the origin of these enigmatic seamount chains as well as the similar nearby Mendelssohn Seamounts. (1) Diffuse lithospheric extension results in the formation of these seamounts until the initiation of the Kula-Pacific spreading center in the north at 84–79 Ma, which alleviates the tension. (2) Shear-driven upwelling of enriched mantle material beneath young oceanic lithosphere results in an age-progressive seamount track that is approximately perpendicular to the spreading ridge. Here we show that all sampled seamounts proximal to the Northwestern Hawaiian Ridge are intraplate in nature, but their formations can be attributed to both plume and plate processes.

Volcanic eruptions provide rare opportunities to witness the biological recolonization of areas covered by new lava flows by effectively resetting the ecological succession clock to zero. The role of submarine volcanic eruptions as disturbance events and the resulting patterns of ecological succession have mainly been studied in hydrothermal vent ecosystems. However, the effects of submarine volcanic eruptions as disturbance forces have rarely been studied in non-vent ecosystems, particularly on seamounts. Here, we document the early stages of ecological succession of non-vent benthic communities inhabiting the summit caldera of the active Vailulu’u submarine volcano in American Samoa. Sitting above the Samoan volcanic hotspot, Vailulu’u is the youngest volcano of the Samoan chain. Repeated mapping of Vailulu’u in 1999, 2005, 2006, 2012, and 2017 revealed the progressive growth of a new cone named Nafanua. In 18 years, the cone grew >300 meters in height from a starting depth of ~1000 meters below sea level (mbsl). The differential analyses of this time-series bathymetry dataset enabled the assignment of maximum age ranges to different portions of the new cone. High-definition ROV imagery collected in 2017 revealed patterns of community structuring consistent with ecological succession: newly erupted seafloor contained a subset of the benthic species found on older seafloor. Furthermore, individual animal sizes in the younger seafloor zones were smaller than in the older zones. This unusual interdisciplinary combination of geological and biological observations provides constraints on which deep-sea animals recolonize new seafloor after a major disturbance event and how quickly. This knowledge could be applied to identify signs and states of recovery from anthropogenic disturbances by a deep seamount ecosystem.

Volcanic hotspots are thought to initially form by melting in an upwelling mantle plume head followed by melting of the plume tail. Plate motion then generates an age progressive volcanic track originating from a large igneous province that connects to an active hotspot. However, the most voluminous large igneous province, the ~120 Ma Ontong-Java Nui Plateau (OJP-Nui) in the mid-Pacific, appears to lack such a volcanic track. Although the Louisville hotspot track was originally proposed as a candidate, limited constraints for Pacific absolute plate and plume motion prior to 80 Ma suggest a mismatch[1]. Existing Pacific models rely on age-distance data from the continuous Hawaii-Emperor and Louisville volcanic tracks, but their seamounts older than ~80 Ma are now subducted, and elsewhere on the Pacific plate only discontinuous and sparse seamount tracks can be found that formed prior to 80 Ma[2–7]. These existing models require ~1,200 km of latitudinal motion for the Louisville plume to also erupt the OJP-Nui1, yet paleolatitude estimates from to ~70 Ma to today remain within error of its present location[8,9] and suggest that any major amount of Louisville plume motion should precede that time. Here we provide evidence from geochemistry and eruption ages[9–14] demonstrating that Samoa and Rurutu-Arago are the longest-lived Pacific hotspots that can be traced back to ~120 Ma (and older) in the West Pacific where they subduct into the Mariana Trench. These newly defined tracks provide for an alternative Pacific absolute plate motion model, with better constraints for a plate rotation between 80-100 Ma, and allow us to establish Louisville as the missing volcanic track for OJP-Nui without requiring major plume motion.

Models for hotspot volcanism suggest a rising plume head forming large igneous provinces (LIP) followed by a timetransgressive volcanic track.However, the Ontong Java Plateau (OJP)-the most voluminous LIP in the geologic record-lacks such a volcanic track and most current absolute plate motion (APM) models do not extend 'robustly' prior to 80 Ma as these APM models are confined by the age of subduction of Louisville and Hawaii hotspots.Movement of the Hawaiian hotspot independent from Louisville and Rurutu-Arago during the Emperor Stage between 50-80 Ma further restricts APM modelling beyond 80 Ma.Early paleomagnetic data suggests Louisville as a candidate for OJP's associated hotspot track, though current APM models would require significant plume motion for this to be accurate and rely on atypical structures with unclear relationships to typical hotspot chains.During the KM2201 expedition in the West Pacific Seamount Province dredges were recovered from 42 seamounts along the hypothesized extensions of the Rurutu-Arago and Samoa hotspots to update existing APM models for the Pacific Plate extending up to 120 Ma.By combining Sr-Nd-Pb-Hf isotope fingerprinting and 40 Ar/ 39 Ar dating of the oldest portion of Rurutu-Arago and Samoa, these hotspot tracks can be adequately defined as long-lived, intraplate anchor points for APM modelling beyond 80 Ma and up to possibly 120 Ma.Rurutu and neighboring Macdonald Hotspot have overlapping unique HIMU composition endmember with a ~10 Myr offset in age progressions.Similarly, late-stage Samoa and Rarotonga and the Cook-Austral Islands have overlapping EM1 isotopic signatures but a ~15 Myr difference in age progressions. 40 Ar/ 39 Ar dating of recovered basalt phases of hornblende, biotite, plagioclase, clinopyroxene and/or groundmass will be conducted to develop a high-resolution age analysis of these time-transgressive features.We hypothesize that newly defined Rurutu will have a westward age progression from ~80-120 Ma approaching the Mariana's trench.Similarly, Samoa-Magellan will likely continue a northward age progression from ~80-100 Ma.Utilizing 40 Ar/ 39 Ar dating and Sr-Nd-Pb-Hf isotope geochemistry to develop a highresolution age vs. composition dataset, we will extend understanding of Pacific plate motion into the Cretaceous and assess the association between OJP and the Louisville Hotspot Trail.

To deconvolve contributions from the four overlapping hotspots that form the "hotspot highway" on the Pacific plate-Samoa, Rarotonga, Arago-Rurutu, and Macdonald-we geochemically characterize and/or date (by the 40Ar/39Ar method) a suite of lavas sampled from the eastern region of the Samoan hotspot and the region "downstream" of the Samoan hotspot track. We find that Papatua seamount, located similar to 60 km south of the axis of the Samoan hotspot track, has lavas with both a HIMU (high mu = U-238/Pb-204) composition (Pb-206/Pb-204 = 20.0), previously linked to one of the Cook-Austral hotspots, and an enriched mantle I (EM1) composition, which we interpret to be rejuvenated and Samoan in origin. We show that these EM1 rejuvenated lavas at Papatua are geochemically similar to rejuvenated volcanism on Samoan volcanoes and suggest that flexural uplift, caused by tectonic forces associated with the nearby Tonga trench, triggered a new episode of melting of Samoan mantle material that had previously flattened and spread laterally along the base of the Pacific plate under Papatua, resulting in volcanism that capped the previous HIMU edifice. We argue that this process generated Samoan rejuvenated volcanism on the older Cook-Austral volcano of Papatua. We also study Waterwitch seamount, located similar to 820 km WNW of the Samoan hotspot, and provide an age (10.49 +/- 0.09 Ma) that places it on the Samoan hotspot trend, showing that it is genetically Samoan and not related to the Cook-Austral hotspots as previously suggested. Consequently, with the possible exception of the HIMU stage of Papatua seamount, there are currently no known Arago-Rurutu plume-derived lava flows sampled along the swath of Pacific seafloor that stretches between Rose seamount (similar to 25 Ma) and East Niulakita seamount (similar to 45 Ma), located 1400 km to the west. The "missing" similar to 20-million-year segment of the Arago-Rurutu hotspot track may have been subducted into the northern Tonga trench, or perhaps was covered by subsequent volcanism from the overlapping Samoan hotspot, and has thus eluded sampling. Finally, we explore tectonic reactivation as a cause for anomalously young volcanism present within the western end of the Samoan hotspot track.

Exchange plays a number of roles within societies, including the provisioning of necessary and prestige resources. The elucidation of these different roles requires documenting how different kinds of material were used and how these resources became distributed. These studies are particularly prominent in Polynesia, especially the Sāmoan archipelago. However, the nature and scale of artifact transfer within and outside the archipelago are debated given deficiencies in the empirical record. Here, we remedy this situation by examining trends in Sāmoan intra-archipelago exchange using geochemical and limited technological analyses of a lithic assemblage from the Manu‘a group of the Sāmoan archipelago. Our results indicate that material from multiple basalt sources is present, including several sources outside the Manu‘a group. It is apparent that this nonlocal material was used differently than local material as 95% of analyzed adzes were manufactured of the former. However, there is no evidence to suggest that this nonlocal material was differentially distributed or controlled at the scale of the group or site. We argue that this is evidence of decentralized exchange and that imported materials became common pool resources to support community resiliency and sustainability.

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.

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.

A new AGU book presents a multidisciplinary perspective on the dynamic processes occurring in Earth's mantle.