More Like this

1. Insights into the Early Volcanic History of the Walvis Ridge recorded by Chemostratigraphy: Preliminary Data IODP Expedition 391 Site U1575

   Nelson, Wendy R; Greenwald, Z; Bowers, R; Shervais, J S; Potter, K E; White, D; Scholpp, J; Widdowson, M; Tshiningayamwe, M; Hoernle, K; et al (December 2023, American Geophysical Union)

   The Walvis Ridge system consists of a series of seamounts, ridges, and plateaus formed during the opening of the southern Atlantic Ocean since ~135 Ma. International Ocean Discovery Program Expeditions (IODP) 391 and 397T drilled six sites along the length of the hotspot track to understand the magmatic processes associated with evolving plume-ridge systems. The oldest drilled segment of the ridge system – Frio Ridge – extends from the Etendeka flood basalts in Namibia westward into the Atlantic Ocean. Site U1575 is on the Frio Ridge and is the closest site to the African continent. The site drilled 118.9 m of igneous basement with 70.7 m (59.5%) of recovery. The recovered core consisted of alternating sequences of submarine pillow lavas and sheet flows, some of which were massive (up to 21 m thick). Preliminary major and trace element data demonstrate the basaltic lavas are fractionated (MgO = 4.8-6.4 wt. %) with modest TiO2 contents (1.5-2.7 wt. %). The upper 52 m of igneous section (214-267 mbsf) are geochemically consistent throughout the various eruptive styles. However, an abrupt compositional shift to lavas with lower incompatible element abundances (TiO2, Zr, Sr, Nb, La, etc.) from 274-311 mbsf demonstrates a clear shift in magmatic source contributions. Below this, the lavas return to compositions similar to the upper portion of the hole. Shipboard natural gamma radiation (NGR) and magnetic susceptibility (MS) measurements correlate with mineralogical and compositional changes. Specifically, decreases in NGR correlate well with decreases in K2O, Sr, Y, and Zr. MS is positively correlated with zones containing olivine. Trace element discrimination plots demonstrate a dual character: Ti-V relationships are strongly MORB-like while Th/Nb suggests the lavas have both MORB and plume characteristics, consistent with the formation of the Frio Ridge through plume-ridge interaction. Elevated Zr/Nb and Y/Nb values are also consistent with a hybrid source. The composition of this core contrasts sharply with cores recovered from the younger Guyot Province to the southwest. Sites U1578 and U1585 have episodes of higher TiO2 contents (>3.5 wt. %) with trace element signatures (e.g. low Zr/Nb & Y/Nb) indicative of a pronounced plume component, consistent with an intraplate setting for the formation of the Guyot Province. 

   more » « less
2. 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. 

   more » « less
3. Awakening of Maunaloa Linked to Melt Shared from Kīlauea’s Mantle Source

   https://doi.org/10.1093/petrology/egae121  

   Pietruszka, Aaron J; Heaton, Daniel E; Marske, Jared P; Norman, Marc D; Robbins, Mahinaokalani G; Mershon, Reed B; Lynn, Kendra J; Downs, Drew T; Steiner, Arron R; Rhodes, J Michael; et al (December 2024, Journal of Petrology)

   Abstract Maunaloa—the largest active volcano on Earth—erupted in 2022 after its longest known repose period (~38 years) and two decades of volcanic unrest. This eruptive hiatus at Maunaloa encompasses most of the ~35-year-long Puʻuʻōʻō eruption of neighboring Kīlauea, which ended in 2018 with a collapse of the summit caldera and an unusually voluminous (~1 km3) 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 Kīlauea 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 Kīlauea or Maunaloa on a timescale of decades. This process led to a correlated temporal variation in 206Pb/204Pb and 87Sr/86Sr 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 Kīlauea reached a minimum from ~2000 to 2010, which coincides with an increase in seismicity and inflation at the summit of Maunaloa. Thereafter, a reversal in Nb/Y at Kīlauea 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 Kīlauea 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 Kīlauea 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 Kīlauea. 

   more » « less
4. Trace Element and Isotopic Evidence for Recycled Lithosphere from Basalts from 48 to 53°E, Southwest Indian Ridge

   https://doi.org/10.1093/petrology/egaa068  

   Wang, Jixin; Zhou, Huaiyang; Salters, Vincent J; Dick, Henry J; Standish, Jared J; Wang, Conghui (June 2020, Journal of Petrology)

   null (Ed.)

   Abstract Mantle source heterogeneity and magmatic processes have been widely studied beneath most parts of the Southwest Indian Ridge (SWIR). But less is known from the newly recovered mid-ocean ridge basalts from the Dragon Bone Amagmatic Segment (53°E, SWIR) and the adjacent magmatically robust Dragon Flag Segment. Fresh basalt glasses from the Dragon Bone Segment are clearly more enriched in isotopic composition than the adjacent Dragon Flag basalts, but the trace element ratios of the Dragon Flag basalts are more extreme compared with average mid-ocean ridge basalts (MORB) than the Dragon Bone basalts. Their geochemical differences can be explained only by source differences rather than by variations in degree of melting of a roughly similar source. The Dragon Flag basalts are influenced by an arc-like mantle component as evidenced by enrichment in fluid-mobile over fluid-immobile elements. However, the sub-ridge mantle at the Dragon Flag Segment is depleted in melt component compared with a normal MORB source owing to previous melting in the subarc. This fluid-metasomatized, subarc depleted mantle is entrained beneath the Dragon Flag Segment. In comparison, for the Dragon Bone axial basalts, their Pb isotopic compositions and their slight enrichment in Ba, Nb, Ta, K, La, Sr and Zr and depletion in Pb and Ti concentrations show resemblance to the Ejeda–Bekily dikes of Madagascar. Also, Dragon Bone Sr and Nd isotopic compositions together with the Ce/Pb, La/Nb and La/Th ratios can be modeled by mixing the most isotopically depleted Dragon Flag basalts with a composition within the range of the Ejeda–Bekily dikes. It is therefore proposed that the Dragon Bone axial basalts, similar to the Ejeda–Bekily dikes, are sourced from subcontinental lithospheric Archean mantle beneath Gondwana, pulled from beneath the Madagascar Plateau. The recycling of the residual subarc mantle and the subcontinental lithospheric mantle could be related to either the breakup of Gondwana or the formation and accretion of Neoproterozoic island arc terranes during the collapse of the Mozambique Ocean, and is now present beneath the ridge. 

   more » « less
5. Near-zero 33S and 36S anomalies in Pitcairn basalts suggest Proterozoic sediments in the EM-1 mantle plume

   https://doi.org/10.1016/j.epsl.2022.117422  

   Labidi, Jabrane; Dottin, James W.; Clog, Matthieu; Hemond, Christophe; Cartigny, Pierre (April 2022, Earth and planetary science letters)

   Volcanic rocks erupted among Pitcairn seamounts sample a mantle plume that exhibits an extreme Enriched Mantle-1 signature. The origin of this peculiar mantle endmember remains contentious, and could involve the recycling of marine sediments of Archean or Proterozoic ages, delaminated units from the lower continental crust, or metasomatized peridotites from a lithospheric mantle. Here, we report the sulfur multi-isotopic signature (32S, 33S, 34S, 36S) of 15 fresh submarine basaltic glasses from three Pitcairn seamounts. We observe evidence for magmatic degassing of sulfur from melts erupted ∼2,000 meters below seawater level (mbsl). Sulfur concentrations are correlated with eruption depth, and range between 1300 ppm S (collected ∼ 2,500 mbsl) and 600 ppm S (∼2,000 mbsl). The δ34S values can be accounted for under equilibrium isotope fractionation during degassing, with αgas-melt between 1.0020 and 1.0001 and starting δ34S values between −0.9‰ and +0.6‰. The δ34S estimates are similar or higher than MORB signatures, suggesting the contribution of recycled sulfur with a ∼ 1‰ 34S enrichment compared to the Pacific upper mantle. The Δ33S and Δ36S signatures average at +0.024±0.007‰ and +0.02±0.07‰ vs. CDT, respectively (all 1σ). Only Δ33S is statistically different from MORB, by +0.02‰. The Δ33S enrichment is invariant across degassing and sulfide segregation. We suggest it reflects a mantle source enrichment rather than a high-temperature fractionation of S in the basalts. Despite the small magnitude of the 33S-36S variations, our data require a substantial amount of recycled sulfur overwhelm the Pitcairn mantle source. We show that models involving metasomatized peridotites, lower crust units, or Archean sediments, may be viable, but are restricted to narrow sets of circumstances. Instead, scenarios involving the contribution of Proterozoic marine sediments appear to be the most parsimonious explanation for the EM-1 signature at Pitcairn. 

   more » « less