An official website of the United States government
Abstract In 2015 a geothermal exploration well was drilled on the island of Tutuila, American Samoa. The sample suite from the drill core provides 645 m of volcanic stratigraphy from a Samoan volcano, spanning 1.45 million years of volcanic history. In the Tutuila drill core, shield lavas with an EM2 (enriched mantle 2) signature are observed at depth, spanning 1.46 to 1.44 Ma. These are overlain by younger (1.35 to 1.17 Ma) shield lavas with a primordial “common” (focus zone) component interlayered with lavas that sample a depleted mantle component. Following ~1.15 Myr of volcanic quiescence, rejuvenated volcanism initiated at 24.3 ka and samples an EM1 (enriched mantle 1) component. The timing of the initiation of rejuvenated volcanism on Tutuila suggests that rejuvenated volcanism may be tectonically driven, as Samoan hotspot volcanoes approach the northern terminus of the Tonga Trench. This is consistent with a model where the timing of rejuvenated volcanism at Tutuila and at other Samoan volcanoes relates to their distance from the Tonga Trench. Notably, the Samoan rejuvenated lavas have EM1 isotopic compositions distinct from shield lavas that are geochemically similar to “petit spot” lavas erupted outboard of the Japan Trench and late stage lavas erupted at Christmas Island located outboard of the Sunda Trench. Therefore, like the Samoan rejuvenated lavas, petit spot volcanism in general appears to be related to tectonic uplift outboard of subduction zones, and existing geochemical data suggest that petit spots share similar EM1 isotopic signatures.
more »
« less
Distinguishing Volcanic Contributions to the Overlapping Samoan and Cook-Austral Hotspot Tracks
Abstract 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 ~60 km south of the axis of the Samoan hotspot track, has lavas with both a HIMU (high μ = 238U/204Pb) composition (206Pb/204Pb = 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 ~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 (~25 Ma) and East Niulakita seamount (~45 Ma), located 1400 km to the west. The “missing” ~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.
more »
« less
- PAR ID:
- 10344409
- Date Published:
- Journal Name:
- Journal of Petrology
- Volume:
- 63
- Issue:
- 5
- ISSN:
- 0022-3530
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
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.more » « less
-
Abstract 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 ~2° 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.more » « less
-
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.more » « less
-
ABSTRACT Hotspots are identified by time‐transgressive, linear chains of volcanoes across the crust. The existence of off‐axis or out‐of‐sequence volcanism, where volcanism does not fit in the age progression along a hotspot track, complicates hotspot identification and hotspot‐lithosphere interaction. The Snake River plain–Yellowstone (SRPY) volcanic province is the archetypal example of a continental hotspot, and south‐southeast of Yellowstone, we document ~8–0.5 Ma magmatism. These off‐axis and out‐of‐sequence SRPY rocks formed in an intraplate setting but geochemically resemble subduction zone magmas, which we attribute to metasomatism of Archean Wyoming craton mantle. Off‐axis volcanism exists where mantle upwelling and associated extension occurs (e.g., oceanic hotspots and continental/oceanic rifts). We suggest that off‐axis SRPY magmatism peripheral to Yellowstone is a continental hotspot analogue and occurs due to migrating thermal uplift, mantle melting, and associated lithosphere extension, which facilitates small volume melt production and eruption and is an under‐assessed hazard.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/petrology/egac032
