The emergence of the "mush paradigm" has raised several questions for conventional models of magma storage and extraction: how are melts extracted to form eruptible liquid-rich domains? What ...mechanism controls melt transport in mush-rich systems? Recently, reactive flow has been proposed as a major contributing factor in the formation of high porosity, melt-rich regions. Yet, owing to the absence of accurate geochemical simulations, the influence of reactive flow on the porosity of natural mush systems remains under-constrained. Here, we use a thermodynamically constrained model of melt-mush reaction to simulate the chemical, mineralogical, and physical consequences of reactive flow in a multi-component mush system. Our results demonstrate that reactive flow within troctolitic to gabbroic mushes can drive large changes in mush porosity. For example, primitive magma recharge causes an increase in the system porosity and could trigger melt channelization or mush destabilization, aiding rapid melt transfer through low-porosity mush reservoirs.
Abstract Many volcanoes erupt compositionally homogeneous magmas over timescales ranging from decades to millennia. This monotonous activity is thought to reflect a high degree of chemical ...homogeneity in their magmatic systems, leading to predictable eruptive behaviour. We combine petrological analyses of erupted crystals with new thermodynamic models to characterise the diversity of melts in magmatic systems beneath monotonous shield volcanoes in the Galápagos Archipelago (Wolf and Fernandina). In contrast with the uniform basaltic magmas erupted at the surface over long timescales, we find that the sub-volcanic systems contain extreme heterogeneity, with melts extending to rhyolitic compositions. Evolved melts are in low abundance and large volumes of basalt flushing through the crust from depth overprint their chemical signatures. This process will only maintain monotonous activity while the volume of melt entering the crust is high, raising the possibility of transitions to more silicic activity given a decrease in the crustal melt flux.
Abstract
The physicochemical characteristics of sub-volcanic magma storage regions have important implications for magma system dynamics and pre-eruptive behaviour. The architecture of magma storage ...regions located directly above high buoyancy flux mantle plumes (such as Kīlauea, Hawai’i and Fernandina, Galápagos) are relatively well understood. However, far fewer constraints exist on the nature of magma storage beneath ocean island volcanoes that are distal to the main zone of mantle upwelling or above low buoyancy flux plumes, despite these systems representing a substantial proportion of ocean island volcanism globally. To address this, we present a detailed petrological study of Isla Floreana in the Galápagos Archipelago, which lies at the periphery of the upwelling mantle plume and is thus characterized by an extremely low flux of magma into the lithosphere. Detailed in situ major and trace element analyses of crystal phases within exhumed cumulate xenoliths, lavas and scoria deposits indicate that the erupted crystal cargo is dominated by disaggregated crystal-rich material (i.e. mush or wall rock). Trace element disequilibria between cumulus phases and erupted melts, as well as trace element zoning within the xenolithic clinopyroxenes, reveal that reactive porous flow (previously identified beneath mid-ocean ridges) is an important process of melt transport within crystal-rich magma storage regions. In addition, application of three petrological barometers reveals that the Floreana mush zones are located in the upper mantle, at a depth of 23·7 ± 5·1 km. Our barometric results are compared with recent studies of high melt flux volcanoes in the western Galápagos, and other ocean island volcanoes worldwide, and demonstrate that the flux of magma from the underlying mantle source represents a first-order control on the depth and physical characteristics of magma storage.
The flow of high‐temperature and compositionally enriched material between mantle plumes and nearby spreading centers influences up to 30% of the global mid‐ocean ridge system and represents a ...significant, but currently unconstrained, flux of volatiles out of the mantle. Here, we present new analyses of H2O, F, Cl, and S in basaltic glass chips from an archetypal region of plume‐ridge interaction, the Galápagos Spreading Center (GSC). Our data set includes samples from the eastern GSC, on ridge segments that are strongly influenced by the adjacent Galápagos mantle plume, and complements published analyses of volatiles largely from the western GSC. We use forward models of mantle melting to investigate the role of solid and melt‐phase transport from a lithologically heterogeneous (peridotite‐pyroxenite) mantle in plume‐ridge interaction along approximately 1,000 km of the GSC. Our results indicate that the observed geochemical and geophysical variations cannot be recreated by models that only involve solid‐state transfer of material between the Galápagos mantle plume and the GSC. Instead, we show that the geochemical and geophysical data from the GSC are well‐matched by models that incorporate channelized flow of volatile‐rich melts formed at high‐pressures (>3 GPa) in the Galápagos plume stem to the GSC. In addition, our new models demonstrate that channelized flow of enriched, plume‐derived melt can account for up to ∼60% of the H2O outgassed from regions of the GSC, which are most strongly influenced by the Galápagos mantle plume.
Plain Language Summary
Approximately one‐third of Earth’s global mid‐ocean ridge system is influenced by the transfer of compositionally distinct material from nearby upwellings of anomalously hot mantle. Transfer of this plume material to oceanic spreading centers might represent an important mechanism of volatile loss from Earth’s mantle, but there are limited constraints on the quantities of H2O and other volatiles that degas from these plume‐influenced spreading centers. In this study, we evaluate the mechanism of plume‐ridge interaction between the Galápagos mantle plume and the nearby Galápagos Spreading Center (GSC) using new analyses of volatiles in basalts erupted on the ridge. The results from new numerical models demonstrate that the geochemical and geophysical signatures of plume‐ridge interaction along the GSC are best explained if the transport of deep sourced mantle material between the Galápagos mantle plume and GSC occurs in the melt phase rather than as a solid. In addition, our new analyses enable us to constrain the flux of H2O out of the GSC and demonstrate that melt channelization can account for up to ∼60% of the H2O flux out of plume‐influenced ridges.
Key Points
Basalts erupted on segments of the global ridge system adjacent to the Galapagos mantle plume have high volatile (H2O and F) contents
Channelized melt transport between the Galápagos mantle plume stem and the Galápagos Spreading Center (GSC) causes variations in crustal thickness and geochemistry
Plume‐derived volatile‐rich melts contribute up to 20%–60% of the total H2O outflux at the GSC
The 2015 eruption of Wolf volcano was one of the largest eruptions in the Galápagos Islands since the onset of routine satellite‐based volcano monitoring. It therefore provides an excellent ...opportunity to combine geophysical and petrological data, to place detailed constraints on the architecture and dynamics of subvolcanic systems in the western archipelago. We present new geodetic models that show that pre‐eruptive inflation at Wolf was caused by magma accumulation in a shallow flat‐topped reservoir at ~1.1 km, whereas edifice‐scale deformation during the eruption was related to a deflationary source at 6.1–8.8 km. Petrological observations suggest that the erupted material was derived from both a subvolcanic mush and a liquid‐rich magma body. Using a combination of olivine‐plagioclase‐augite‐melt (OPAM) and clinopyroxene‐melt barometry, we show that the majority of magma equilibration, crystallization, and mush entrainment occurred at a depth equal to or greater than the deep geodetic source, with little petrological evidence of material sourced from shallower levels. Hence, our multidisciplinary study does not support a fully transcrustal magmatic system beneath Wolf volcano before the 2015 eruption but instead indicates two discrete storage regions, with a small magma lens at shallow levels and the major zone of magma storage in the lower crust, from which most of the erupted material was sourced. A predominance of lower crustal magma storage has previously been thought typical of subvolcanic systems in the eastern Galápagos Archipelago, but our new data suggest that this may also occur beneath the more active volcanoes of the western archipelago.
Key Points
Combined geophysical and petrological constraints provide a detailed picture of the subvolcanic architecture at Wolf volcano
Wolf is underlain by two discrete magma storage regions: one within the edifice, the other in the lower crust
Almost all the magma ejected during the 2015 eruption of Wolf was derived from the lower crust
•δ56Fe heterogeneity is observed in plume-influenced basalts from the GSC.•The δ56Fe composition of these basalts cannot result from melting of a peridotite.•Lithological heterogeneity in the ...Galápagos mantle plume is required.•δ56Fe heterogeneity of oceanic basalts results from lithological heterogeneity.
The extent of lithological heterogeneity in the Earth's convecting mantle is highly debated. Whilst the presence of pyroxenite in the mantle source regions of Ocean Island Basalts (OIBs) has traditionally been constrained using the minor-element chemistry of olivine phenocrysts, recent studies have shown that the Ni and Mn contents of primitive olivines are influenced by the conditions of mantle melting, as well as magma chamber processes. Nevertheless, constraining the lithological properties of the mantle is important due to its influence on the P-T path followed by solid mantle material during adiabatic ascent, as well as the density of upwelling mantle plumes. We have therefore explored the use of Fe-isotopes as a novel method of tracing lithological heterogeneity in the mantle source regions beneath plume-influenced segments of the global Mid-Ocean Ridge system as well as OIBs.
We present new Fe-isotope (δ56Fe) and trace-element data for 26 basaltic glasses from the plume-influenced Galápagos Spreading Centre to investigate the relative roles of pyroxenite and peridotite in the mantle source region of oceanic basalts. Our data reveals significant heterogeneity in the Fe-isotope composition of the Galápagos Spreading Centre basalts (+0.05 to +0.25‰ δ56Fe), which correlates with key major- and trace-element parameters (e.g. CaO(8)/Al2O3(8), La/Smn). Application of new models developed to calculate Fe-isotope fractionation during mantle melting, alongside Monte Carlo simulations for melting of a 2-component peridotite mantle, show that this variation cannot be caused by changes in melting processes and/or oxygen fugacity of a peridotitic mantle. Instead, our new δ56Fe data is best explained by variations in the proportion of isotopically-heavy pyroxenite-derived melt that contributes to the GSC basalts, and conclusively shows that lithological heterogeneity exists in the Galápagos mantle plume. Our findings have implications for the moderately-heavy δ56Fe compositions measured in plume-influenced basalts from the Society Islands, Rochambeau Ridges of the Lau back-arc basin, and the FAMOUS segment of the Mid-Atlantic Ridge, which we suggest may also represent contribution from pyroxenite-derived melts.
Despite their relatively low concentration in most oceanic basalts, volatile species (e.g. H2O, CO2 and S) have a disproportionately large influence on a wide range of mantle and magmatic processes. ...Yet, constraining the concentration of H2O (and other volatiles) in basaltic magmas is not straightforward as submarine glass analyses are influenced by assimilation of hydrothermal brines, and the melt inclusion record is often reset by post-entrapment processes. Nevertheless, in this study we show that it is possible to reconstruct a detailed history of the volatile content of basaltic magmas through integration of multiple discreet volatile records and careful consideration of secondary processes. We present new analyses of volatiles in olivine-hosted melt inclusions, melt embayments and nominally anhydrous minerals (NAMS, clinopyroxene and orthopyroxene) found in basalts erupted on Floreana Island in the south-eastern Galápagos Archipelago. Our results indicate that the Floreana magmas, which are characterised by the most radiogenic Pb and Sr isotope signatures in the Galápagos Archipelago, contain H2O concentrations between 0.4 and 0.8 wt% (at a melt Mg# of 0.65, where Mg# = Mg/(Mg + Fe) molar). These are marginally greater than the H2O contents of magmas beneath Fernandina in the western Galápagos Archipelago (cf. 0.2–0.7 wt% H2O at Mg# = 0.65). However, while the volatile content of magmas from the western archipelago follow trends defined by concurrent mixing and crystallisation, NAMs from Floreana reveal the presence of rare, volatile-rich magmas (∼2 wt% H2O) that form as a consequence of reactive porous flow in mush-dominated magmatic systems beneath the south-eastern Galápagos. Furthermore, the Floreana magmas have similar H2O/light Rare Earth Element ratios to basalts from the western Galápagos but contain F/Nd and Cl/K ratios that are ∼ 2–3 times greater, indicating that the mantle source of the Floreana lavas might represent an important halogen reservoir in the Galápagos mantle plume.
Pediatric-onset ataxias often present clinically as developmental delay and intellectual disability, with prominent cerebellar atrophy as a key neuroradiographic finding. Here we describe a new ...clinically distinguishable recessive syndrome in 12 families with cerebellar atrophy together with ataxia, coarsened facial features and intellectual disability, due to truncating mutations in the sorting nexin gene SNX14, encoding a ubiquitously expressed modular PX domain-containing sorting factor. We found SNX14 localized to lysosomes and associated with phosphatidylinositol (3,5)-bisphosphate, a key component of late endosomes/lysosomes. Patient-derived cells showed engorged lysosomes and a slower autophagosome clearance rate upon autophagy induction by starvation. Zebrafish morphants for snx14 showed dramatic loss of cerebellar parenchyma, accumulation of autophagosomes and activation of apoptosis. Our results characterize a unique ataxia syndrome due to biallelic SNX14 mutations leading to lysosome-autophagosome dysfunction.
Abstract
The flow of high‐temperature and compositionally enriched material between mantle plumes and nearby spreading centers influences up to 30% of the global mid‐ocean ridge system and represents ...a significant, but currently unconstrained, flux of volatiles out of the mantle. Here, we present new analyses of H
2
O, F, Cl, and S in basaltic glass chips from an archetypal region of plume‐ridge interaction, the Galápagos Spreading Center (GSC). Our data set includes samples from the eastern GSC, on ridge segments that are strongly influenced by the adjacent Galápagos mantle plume, and complements published analyses of volatiles largely from the western GSC. We use forward models of mantle melting to investigate the role of solid and melt‐phase transport from a lithologically heterogeneous (peridotite‐pyroxenite) mantle in plume‐ridge interaction along approximately 1,000 km of the GSC. Our results indicate that the observed geochemical and geophysical variations cannot be recreated by models that only involve solid‐state transfer of material between the Galápagos mantle plume and the GSC. Instead, we show that the geochemical and geophysical data from the GSC are well‐matched by models that incorporate channelized flow of volatile‐rich melts formed at high‐pressures (>3 GPa) in the Galápagos plume stem to the GSC. In addition, our new models demonstrate that channelized flow of enriched, plume‐derived melt can account for up to ∼60% of the H
2
O outgassed from regions of the GSC, which are most strongly influenced by the Galápagos mantle plume.
Plain Language Summary
Approximately one‐third of Earth’s global mid‐ocean ridge system is influenced by the transfer of compositionally distinct material from nearby upwellings of anomalously hot mantle. Transfer of this plume material to oceanic spreading centers might represent an important mechanism of volatile loss from Earth’s mantle, but there are limited constraints on the quantities of H
2
O and other volatiles that degas from these plume‐influenced spreading centers. In this study, we evaluate the mechanism of plume‐ridge interaction between the Galápagos mantle plume and the nearby Galápagos Spreading Center (GSC) using new analyses of volatiles in basalts erupted on the ridge. The results from new numerical models demonstrate that the geochemical and geophysical signatures of plume‐ridge interaction along the GSC are best explained if the transport of deep sourced mantle material between the Galápagos mantle plume and GSC occurs in the melt phase rather than as a solid. In addition, our new analyses enable us to constrain the flux of H
2
O out of the GSC and demonstrate that melt channelization can account for up to ∼60% of the H
2
O flux out of plume‐influenced ridges.
Key Points
Basalts erupted on segments of the global ridge system adjacent to the Galapagos mantle plume have high volatile (H
2
O and F) contents
Channelized melt transport between the Galápagos mantle plume stem and the Galápagos Spreading Center (GSC) causes variations in crustal thickness and geochemistry
Plume‐derived volatile‐rich melts contribute up to 20%–60% of the total H
2
O outflux at the GSC
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