Plume Material Research Articles

Currents and topography drive assemblage distribution on an active hydrothermal edifice

The deep sea is characterized by a wide range of landscapes, including complex features where topography and currents interact to form highly heterogeneous habitats. In addition to a complex topography, hydrothermal vent environments are characterized by strong environmental gradients that structure the spatial distribution of biological communities. The role of vent fluid temperature and chemical composition on species distribution is now well understood, but investigations on the effects of the complex sulfide edifice topography are scarce. Here, we used a novel approach combining 3D photogrammetric reconstruction, in situ environmental measurements and modeling to characterize assemblage distribution on the active edifice Eiffel Tower (Lucky Strike, Mid-Atlantic Ridge). Through the analysis of a high-resolution 3D model of the edifice, we show that assemblage distribution along with hydrothermal activity vary with their position on the edifice. Although physical terrain variables had a minor effect on assemblage distribution, the distance from fluid exits explained the distribution of most assemblages. However, these particular variables did not significantly explain the distribution of medium-sized Bathymodiolus azoricus mussels, the dominant assemblage on the edifice. Similarly, proximity to fluid exits only partially accounted for the distribution of microbial mats throughout the edifice. By modeling the current-driven dispersion of hydrothermal plumes around the edifice, we demonstrated that differences in mussel sizes may be due to differences in exposure time to currents bringing plume material. For the first time, we provide evidence that hydrothermal plumes can affect faunal assemblages meters away from fluid exits and that this relatively long-distance effect of vent plumes can fully account for microbial mat distribution throughout the edifice. Our findings extend the area of influence of hydrothermal plumes on vent communities considerably beyond previous estimations and suggest that the interactions between bottom currents, topography and smoker locations should be further investigated and considered as important structuring factors at vents. This novel approach, allowing to cover large areas of the seafloor, is particularly well suited for deep environments where topography and currents interact to form complex oceanographic patterns (e.g. canyons, seamounts). Its application to larger areas and various ecosystems can significantly enhance our understanding of benthic communities’ distribution at large.

Origin of isolated seamounts in the Canary Basin (East Atlantic): The role of plume material in the origin of seamounts not associated with hotspot tracks

AbstractIn contrast to seamount chains, small solitary seamounts/seamount groups have rarely been sampled despite their large number and therefore their origins remain enigmatic. Here we present new 40Ar/39Ar, trace element and Nd‐Hf‐Pb isotope data from the solitary Demenitskoy Seamount, the isolated Tolkien seamount group and the Krylov Seamount and Ridge in the Canary Basin, Central Atlantic Ocean. Their chemical compositions range from intraplate ocean‐island‐basalt (Demenitskoy) to mid‐ocean‐ridge‐basalt (Tolkien and Krylov) types. Lavas from all three seamount groups, however, show geochemical evidence for involvement of enriched Canary/Cape Verde plume material. Seismic tomography shows that large areas around these mantle plumes consist of dispersed low‐velocity material, which could represent diffusely‐upwelling plume mantle. Melts from such upwelling mantle could form isolated seamounts. Diffuse upwelling of plume material is likely to be extremely widespread but has been poorly studied to date.Significance StatementA fundamental question concerns the origin of the hundreds of thousands of solitary seamounts and small isolated clusters of such seamounts on the seafloor of the world's ocean basins. Most of them do not fit into any currently accepted models (e.g. they are not associated with a linear hotspot track or plate boundary processes). Their formation could therefore represent a new kind of intraplate volcanism that in fact could be extremely widespread but has been thus far largely neglected. In this manuscript, we report geochemical data from three isolated seamount sites in the Canary Basin and propose a provocative model for their formation that can also be applied to isolated seamounts elsewhere. Our study is therefore also a plea for the long overdue systematic investigation of small seamount volcanism in the world's ocean basins.I hereby confirm that all the data and interpretations are new and have not been published elsewhere. All co‐authors have been actively involved in this work, have approved the manuscript and agreed to this submission.

Using a coupled dispersion model to estimate depletion of a tritium oxide plume by a forest

Tritium processing facilities may release tritium oxide (HTO) to the atmosphere which poses potential health risks to exposed co-located workers and to offsite individuals. Most radiological consequence analyses determine HTO dose by applying Gaussian plume models to simulate the transport of HTO. Within these models, deposition velocity is used to assess the sum of all deposition processes acting on the plume. While this may account for vegetative and soil uptake or respiration processes, it may currently lack inclusion of the complex interactions within heterogeneous forested environments. In this complex morphology, dispersion patterns are significantly altered by changing flow regimes above and below the forest canopy and by the transfer of plume material across the canopy boundary. To determine the effects of a heterogeneous forest canopy on an airborne HTO plume, a Gaussian plume model coupled with an advection-diffusion plume model was applied to estimate transport in the free atmosphere above the forest and within the forest canopy and understory. During 2012, wind speed and wind direction measurements taken at 5 heights, ranging from 2-m to 28-m, on an instrumented meteorological tower located in a loblolly pine forest at the Department of Energy (DOE) Savannah River Site (SRS), near Aiken, SC. From these measurements, model predictions were made over a full spectrum of meteorological conditions. Deposition and resuspension velocities were calculated based on the model-predicted flux of plume material across the top of the forest canopy. Additionally, net deposition velocity of the plume material was calculated as the difference between the deposition and resuspension velocities. The 1st and 5th percentile net deposition velocities were estimated to be 0.7 cm s−1 and 1.2 cm s−1, respectively.

A high-resolution view of the jets in 3C 465

ABSTRACT We present new high-resolution and high-sensitivity studies of the jets in the WAT source 3C 465, using deep transverse-resolved radio observations from e-MERLIN, and with complementary observations from the Very Large Array (VLA). We derive a lower limit βj = (νj/c) ≳ 0.5 for the jet speed, and an upper limit $\theta _{\rm j}\, \lesssim$ 61° for the jet angle to the line of sight. The jet spectral index (α, defined in the sense S ∝ να) is fairly constant (<αjet > = − 0.7), and spectral flattening within 4.4 kpc of the core coincides with bright knots and is consistent with the site of X-ray particle acceleration at the base of the radio jet found in previous studies. There is little difference between the spectra of the two hotspot components, plausibly indicating that electron populations of the same properties are injected there. The north-west (NW) and south-east (SE) plumes are approximately homologous structures, with variations in mass injection and propagation in external pressure and density gradients in the two regions plausibly accounting for the slightly steeper spectrum in the NW plume, <αNWp> = −1.43 compared with the SE plume, <αSEp> = −1.38. Our synchrotron lifetime model supports plausible reacceleration of particles within the plume materials. Overall, our results show that the first-order Fermi process at mildly relativistic and non-relativistic shocks is the most likely acceleration mechanism at play in 3C 465 and distinguish differences between the acceleration at $\beta _{\rm j}\, \gt $ 0.5 and $\beta _{\rm j}\, \lt $ 0.5. The former case can accelerate electrons to higher Lorentz factors.

Multi-objective optimization of permeable reactive barrier design for Cr(VI) removal from groundwater.

The present study aims to develop a practical approach for the optimal permeable reactive barrier (PRB) design towards Cr(VI) removal from groundwater. Batch and column experiments were performed to investigate the characteristics of the four proposed reactive materials; nanoscale zero-valent iron (Fe0), bimetallic nanoscale zero-valent iron (Fe0/Cu), activated carbon (AC) and sand/zeolite mixture (S/Z). Kinetic analysis and dynamic modeling of the experimental data were implemented to determine the controlling conditions of the reactive performance of the PRB's materials. The sensitivity index of the design parameters was examined as an indicator of their effect on the reactive responses. Moreover, the Response Surface Methodology (RSM) was considered for optimizing the design variables of the PRB based on the practical factorial analysis. Results revealed that Fe0 and Fe0/Cu showed high performance in Cr(VI) removal, with a slight superiority to Fe0, with final removal efficiency values of 89.7 and 84.1%, respectively. Kinetic analysis depicted that pseudo second order was the best fitting model for Cr(VI) removal in the four materials' cases. ANOVA statistical analysis revealed that quadratic polynomial model was the best model, corresponding to the highest correlation efficiency and adequate precision, to describe the relationships in the four PRB's cases between the selected dependent variables; resident time (tR), reactive material mass per sectional area of contaminant plume (M/A) and reactive material cost (CostPRB) towards the independent parameters; barrier thickness (b) and permeability (Kr). Additionally, sensitivity analysis has been conducted which depicted the high sensitivity, in the four PRB's cases, of average pore water velocity within the barrier (vr) vr and Kr with the highest and the second-highest sensitivity index (SI) values towards tR, respectively. The RSM-optimization revealed that Fe0 is the most feasible reactive material, comparing to the other considered materials, with respect to the optimal conditions regarding the long residency (tR=22 days) and low cost (b=0.521m), with around 95.2% desirability of its optimal solution. Overall, the current study represents a significant contribution and a vital step towards an accurate PRB's design based on previously determined optimal conditions.

Mantle plume dynamics at the rear of a retreating slab

SUMMARY In this paper, we present 3-D numerical simulations in which a compositional mantle plume rises through a shallow mantle layer at the rear of a retreating slab. The slab–plume buoyancy flux ratio Bs/Bp is varied from 3 to 30 over nine slab–plume simulations. The plume causes an overall decrease of the slab retreat rate from 15 to 7 % in the corresponding range $B_s/B_p=[3,30]$. The retreat rate decrease occurs in two stages: the first decrease occurs remotely when plume and slab are hundreds of kilometres apart; the second decrease is linked to the slab–plume-head impact. Continuous tracking of key positions along the plume head and conduit together with velocity profiling further shows a very close interplay between the conduit and plume head dynamics. In particular, the combination of the slab– and plume(head)–induced flows at the rear of the slab increases the advection and tilt of the conduit and causes its flaring with height in the direction parallel to the trench. As a result, the conduit source slowly drifts away from the slab by hundreds of kilometres and flares by one and a half times its original radius over 30 Myr of plume head spreading. The conduit tilt and flaring result in an increasingly unbalanced azimuthal distribution of the incoming plume flux from the feeding conduit into the head. These changes in the feeding conditions coupled with the mantle flow at the level of the plume head lead to the asymmetric spreading of plume material beneath the plate in the preferential direction that is parallel to the trench. Upon its arrival against the slab, it can be a front of buoyant material set to subduct along the slab width that has widened up to two and a half times its initial dimension. In nature, it is expected to extend from hundreds to thousands of kilometres depending on the slab–plume buoyancy flux ratio. To our knowledge, this study is the first to highlight the inter-relationships between a plume head and its feeding conditions in the plume source region.

Dynamic Magma Storage at Near‐Ridge Hot Spots: Evidence From New Galápagos Gravity Data

AbstractA morphological dichotomy exists between the active western and older (>1–2.5 Ma) eastern volcanoes of the Galápagos Archipelago. All of the young shield volcanoes in the west have calderas, but none are present on the older volcanoes in the east. This striking difference suggests that there has been a change in volcanic construction and magmatic supply processes, a finding dissimilar to the prevailing Hawaiian model of hot spot evolution. Bouguer anomaly highs (30–50 mGal) consistent with dense cumulate bodies are measured over these calderas. In contrast, we present new gravity data from Santa Cruz and San Cristóbal islands that lack comparable gravity highs. We propose that formation of shallow magma reservoirs and their associated Bouguer anomaly highs were inhibited during evolution of the eastern volcanoes because the proximal Galápagos Spreading Center diverted plume material more efficiently ~1–2 Ma when the spreading center was ~100 km closer to the plume. The difference in caldera expression between the western and eastern islands may be a surface expression of this process. These results suggest that plume‐ridge interaction may play a first‐order role in the evolution of magmatic plumbing systems of near‐ridge ocean islands, which account for one third of hot spot systems.

Multi-stage evolution of the Xuhuai rift: Insights from the occurrence and compositional profiles of doleritic sills in the southeastern margin of the North China Craton

Various types of igneous suites occurred between 930 Ma and 890 Ma in the North China craton are known to represent a large igneous province (LIP). However, the magma plumbing system of this LIP and its potential consequence to a breakup event are poorly understood. We report morphology, crystal size distribution of plagioclase, and whole-rock and mineral geochemistry profiles of this LIP represented by the two decoupled mafic sill complexes (Niutishan and Pingshan) in the Xuhuai basin. In terms of petrography and whole-rock geochemistry, unlike the lower-level doleritic Niutishan sill, the Pingshan sill is subdivided into an upper and a lower sequence that meets at a Sandwich Horizon but lacks stratification. The significant En reversals present an almost M-shaped profile that differs from a C-shaped profile as previously revealed in the Niutishan sill. Quantitative textural analyses show relatively strong plagioclase orientation in the lower sequence of the Pingshan sill, which is attributed to magma flow. The Pingshan sill is interpreted to have been constructed as multiple magma injections from crustal magma chambers based on the crystal size distribution and the varied crystallization pressure (5.1–7.5 kbar) of clinopyroxene crystals.Similar to the far-field radiating Dashigou dyke swarm (c. 925 Ma), the Niutishan sill is enriched in incompatible elements, which may represent the initiation of the Xuhuai rifting. However, the depleted features of the diamond-bearing Pingshan sill and the other coeval doleritic sills (916–890 Ma) were probably related to the subsequent process switched from continental rifting to lithospheric rupture in the divergent stage of the Wilson cycle. The occurrence of the intrusive rocks evolving from an early radiating dyke swarm to later sill complexes indicates a time-transgressive change from radial to planar patterns, implying that it was the upwelling asthenospheric plume material, instead of plate boundary processes, governed the initial and early evolution of this intracontinental rift.

Europa’s surface water ice crystallinity: Discrepancy between observations and thermophysical and particle flux modeling

Physical processing of Europan surface water ice by thermal relaxation, charged particle bombardment, and possible cryovolcanic activity can alter the percentage of the crystalline form of water ice compared to that of the amorphous form of water ice (the “crystallinity”) on Europa’s surface. The timescales over which amorphous water ice is thermally transformed to crystalline water ice at Europan surface temperatures (80–130 K) suggests that the water ice there should be primarily in the crystalline form, however, surface bombardment by charged particles induced by Jupiter’s magnetic field, and vapor deposition of water ice from Europan plumes, can produce amorphous water ice surface deposits on short timescales. The purpose of this investigation is to determine whether the Europan surface water ice crystallinity derived from ground-based spectroscopic measurements is in agreement with the crystallinity expected based upon temperature and radiation modeling. Using a 1D thermophysical model of Europa’s surface, we calculate an integrated full-disk crystallinity of Europa’s leading hemisphere by incorporating the thermal relaxation of amorphous to crystalline water ice and the degradation of crystalline to amorphous water ice by irradiation. Concurrently, we derive the full-disk crystallinity of Europa’s leading hemisphere using a comparison of near-infrared ground-based spectral observations from Grundy et al. (1999), Busarev et al. (2018), and the Apache Point Observatory in Sunspot, NM, with laboratory spectra from Mastrapa et al. (2008) and the Ice Spectroscopy Lab at the Jet Propulsion Laboratory. We calculate a modeled crystallinity significantly higher than crystallinities derived from ground-based observations and laboratory spectra. This discrepancy may be a result of geophysical processes, such as by vapor-deposited plume material, or it may arise from assumptions and uncertainties in the crystallinity calculations.

ИЗОТОПНО-ГЕОХИМИЧЕСКАЯ НЕОДНОРОДНОСТЬ ПЛИОЦЕН-ЧЕТВЕРТИЧНЫХ ВУЛКАНИТОВ КАМЧАТКИ И ПРОБЛЕМА АСТЕНОСФЕРНОГО ДИАПИРИЗМА

Isotope-geochemical material for Pliocene-Quaternary volcanoes of the Kamchatka region is generalized on a cartographic basis. The Sr-isotope anomalies of moderate and elevated radiogenicity, geochemically confirmed, are spatially conjugated. This made it possible to interpret these anomalies not only as a reflection of mantle plume material in the composition of volcanic rocks, but also of its hybrid environment, as a consequence of plum-lithosphere remobilization. The presence of multi-directional geochemical trends made it possible to propose the concept of moving boundary values for the composition of indicator rocks of the intraplate type and adakites, which significantly expanded the possibilities of their diagnostics. The isotope-geochemical heterogeneity of basaltoids of the region is generally determined by the peculiarities of concentration of rocks with intraplate and adakite geochemical characteristics, which allows considering the asthenospheric diapirism as the main factor of petrogenesis of Pliocene-Quaternary volcanism in Kamchatka.

Isotope-geochemical (Sm–Nd, Rb–Sr, REE, HFSE) composition of the University foidolite-gabbro pluton, Kuznetsk Alatau ridge, Siberia

The University foidolite-gabbro pluton is located among the Cambrian carbonate-volcanogenic deposits. Its composition is dominated by moderately-alkaline and alkaline mafic rocks, broken by dikes of ijolite-urtites, nepheline and alkaline syenites. The chemical composition of igneous rocks is characterized by low silica contents (SiO2 = 41–49 wt. %), wide variations of alkalinity (Na2O + K2O = 3–19 wt. %; Na2O / K2O = 1.2–7.2 wt. %), low titanium content (TiO2 = 0.07 1.59 wt. %) and high alumina content (Al2O3 = 15–28 wt. %), which corresponds to the K-Na derivatives of the basic alkaline formation. By the content of rare earth elements, alkaline rocks (104–246 ppm; La/Yb(n) = 5.79–12.73) are more differentiated derivatives than gabbro (94–111 ppm; La/Yb(n) = 6.87‑6.95). All varieties are characterized by low concentrations of most highly charged elements (Nb, Ta, Zr, Hf + Y), which in terms of accumulation are located between the basalts of oceanic islands and basalts of island arcs. The presence of negative Nb–Ta anomaly and the relative enrichment of Rb, Ba, Sr, and U indicate the probable interaction of plume material with previously formed accretionary complexes of subduction zones. The primary isotope 87Sr/86Sr ratio (~ 0.705 – 0.706) and a wide range of εNd (T) from +3.2 to +8.7 in the rocks also indicate a mantle-crustal nature and a complex geodynamic setting of the Paleozoic alkaline magmatism of the Kuznetsk Alatau. The obtained results of Sm‑Nd dating suggest the formation of moderately-alkaline gabbroids in the Early Paleozoic (494–491 ± 36 Ma), with the intrusion of dikes of alkaline rocks of the Middle Paleozoic age (394 ± 16 and 389 ± 37 Ma).

The Cenozoic magmatism of East Africa: Part V – Magma sources and processes in the East African Rift

The generation of magmas in the East African Rift System (EARS) is largely the result of either: (A) melting of easily fusible compositions located within the lithospheric mantle due to thermobaric perturbations of the lithosphere, or (B) melting of the convecting upper mantle due to decompression caused by thinning of the plate during extension. Melt generated from amphibole- or phlogopite-bearing metasomes within the lithospheric mantle yields alkaline, silica-undersaturated lavas, while more silica-saturated lavas are primarily a function of melting material within the convecting upper mantle. Sourcing of silica-undersaturated melts within the lithospheric mantle is consistent with the observed tendency for initial melts within any given region to exhibit trace element characteristics consistent with melting of lithospheric metasomes, likely reflecting the initial destabilization and thinning of the lithospheric mantle. With continued lithospheric thinning, the trend towards more silica-saturated compositions coincides with a shift towards compositions interpreted as melting of the convecting upper mantle. Contributions from these two sources may oscillate where extension is pulsed – melts of the convecting upper mantle are favored during periods of plate thinning; melting of either existing or recently formed metasomes may be favored during periods of relative extensional quiescence. The isotopic systematics of East African magmatism reveals significant complexity as to the specific reservoirs that may participate in the melting processes noted above. The lithospheric mantle beneath East Africa has undergone enrichment through the percolation of sub-lithospheric derived melts and fluids over an extended interval, which close to the Tanzania craton has resulted in a layered lithospheric mantle exhibiting extreme isotopic ratios. Elsewhere, the lithospheric mantle has also undergone enrichment but given the more juvenile age of this lithosphere, less extreme isotopic values have developed. Material rising from the African Large Low Shear Velocity Province (LLSVP) has also metasomatized the lithospheric mantle, and thus lavas exhibiting a trace element signature linked to melting within the lithospheric mantle may exist as any number of reservoirs or mixtures of the same. Material derived from the convecting upper mantle incorporates the Afar Plume endmember, a depleted mantle endmember, and some form of lithospheric endmember. The isotopic characteristics of magma suites from throughout the region form arrays that broadly converge on the composition of the Afar Plume, despite some complexity where the plume material has formed a hybrid plume-lithosphere component. The convergence of these arrays strongly supports a model whereby the prevalent composition of material rising from the African LLSVP beneath the EARS is broadly equivalent to the composition of the Afar Plume.

Intra-plate volcanism in North Queensland and eastern new Guinea: A cryptic mantle plume?

Intra-plate volcanism in NE Australia, the eastern Highlands of New Guinea and along the Papuan Peninsula has been reasonably continuous over the Pliocene and Quaternary, without age progression, despite rapid movement of the Australian plate towards the north (∼7 cm/yr). Global seismic tomography indicates a strong zone of reduced seismic wavespeed near the core-mantle boundary beneath the Coral Sea, between Australia and New Guinea, yet unlike the majority of such features, there is no obvious volcanic ‘hotspot’ at Earth’s surface. By analysing a combined global and regional tomography model, we suggest here that since 20 Ma, remnants of past subduction, imaged as fast wavespeed zones in seismic tomography, have impeded any direct upwelling from depth. The spatio-temporal patterns and geochemical signature of volcanism in this region, however, suggests that some plume material has made its way through this maze of slab remnants, to impinge on the strong lithospheric step associated with the edge of the thick North Australian craton, which extends into New Guinea. We suggest that following the arrival of the extended Australian continent into the zone of influence of this cryptic mantle plume at ∼10 Ma, the combination of largely blocked upward flow and shallow edge- and shear-driven processes modulates the regional flow regime to spawn volcanism at the observed locations in NE Australia and New Guinea.

Late Cretaceous (99-69 Ma) basaltic intraplate volcanism on and around Zealandia: Tracing upper mantle geodynamics from Hikurangi Plateau collision to Gondwana breakup and beyond

Margins resulting from continental breakup are generally classified as volcanic (related to flood basalt volcanism from a starting plume head) or non-volcanic (caused by tectonic processes), but many margins (breakups) may actually be hybrids caused by a combination of volcanic and tectonic processes. It has been postulated that the collision of the Hikurangi Plateau with the Gondwana margin ∼110 Ma ago caused subduction to cease, followed by large-scale extension and ultimately breakoff of the Zealandia micro-continent from West Antarctica through seafloor spreading which started at ∼85 Ma. Here we report new geochemical (major and trace element and Sr-Nd-Pb-Hf isotope) data for Late Cretaceous (99-69 Ma) volcanism from Zealandia, which include the calc-alkalic, subduction-related Mount Somers (99-96 Ma) and four intraplate igneous provinces: 1) Hikurangi Seamount Province (99-88 Ma), 2) Marlborough Igneous Province (98-94 Ma), 3) Westland Igneous Province (92-69 Ma), and 4) Eastern Chatham Igneous Province (86-79 Ma). Each of the intraplate provinces forms mixing arrays on incompatible-element and isotope ratio plots between HIMU (requiring long-term high μ=238U/204Pb) and either a depleted (MORB-source) upper mantle (DM) component or enriched continental (EM) type component (located in the crust and/or upper mantle) or a mixture of both. St. Helena end member HIMU could be the common component in all four provinces. Considering the uniformity in composition of the HIMU end member despite the type of lithosphere (continental, oceanic, oceanic plateau) beneath the igneous provinces, we attribute this component to a sublithospheric source, located beneath all volcanic provinces, and thus most likely a mantle plume. We propose that the plume material rose beneath the active Gondwana margin and flowed along the subducting lithosphere beneath the Hikurangi Plateau and neighboring seafloor and through slab tears/windows beneath the Gondwana (later to become Zealandia) continental lithosphere. We conclude that both plateau collision, resulting in subduction cessation, and the opening of slab tears/windows, allowing hot asthenosphere and/or plume material to upwell to shallow depths, were important in causing the breakup of Zealandia from West Antarctica. Combined tectonic-volcanic processes are also likely to be responsible for causing breakup and the formation of other hybrid type margins.

Low-mass nitrogen-, oxygen-bearing, and aromatic compounds in Enceladean ice grains

ABSTRACT Saturn’s moon Enceladus is erupting a plume of gas and ice grains from its south pole. Linked directly to the moon’s subsurface global ocean, plume material travels through cracks in the icy crust and is ejected into space. The subsurface ocean is believed to be in contact with the rocky core, with ongoing hydrothermal activity present. The Cassini spacecraft’s Ion and Neutral Mass Spectrometer (INMS) detected volatile, gas phase, organic species in the plume and the Cosmic Dust Analyser (CDA) discovered high-mass, complex organic material in a small fraction of ice grains. Here, we present a broader compositional analysis of CDA mass spectra from organic-bearing ice grains. Through analogue experiments, we find spectral characteristics attributable to low-mass organic compounds in the Enceladean ice grains: nitrogen-bearing, oxygen-bearing, and aromatic. By comparison with INMS results, we identify low-mass amines [particularly (di)methylamine and/or ethylamine] and carbonyls (with acetic acid and/or acetaldehyde most suitable) as the best candidates for the N- and O-bearing compounds, respectively. Inferred organic concentrations in individual ice particles vary but may reach tens of mmol levels. The low-mass nitrogen- and oxygen-bearing compounds are dissolved in the ocean, evaporating efficiently at its surface and entering the ice grains via vapour adsorption. The potentially partially water soluble, low-mass aromatic compounds may alternatively enter ice grains via aerosolization. These amines, carbonyls, and aromatic compounds could be ideal precursors for mineral-catalysed Friedel–Crafts hydrothermal synthesis of biologically relevant organic compounds in the warm depths of Enceladus’ ocean.

Pangea and the Lower Mantle

AbstractWe show that the peripheral Pangea subduction zone closely followed a polar great circle. We relate it to the band of faster‐than‐average velocities in lowermost mantle. Both structures have an axis of symmetry in the equatorial plane. Assuming geologically long‐term stationarity of the deep mantle structure, we propose to use the axis of symmetry of Pangea to define an absolute reference frame. This reference frame is close to the slab remnants and NNR frames of reference but disagrees with hot spot‐based frames. We apply this model to the last 400 Myr. We show that a hemispheric supercontinent appeared as early as 400 Ma. However, at 400 Ma, the axis of symmetry was situated quite far south and progressively migrated within the equatorial plane that it reached at 300 Ma. From 300 to 110–100 Ma, it maintained its position within the equatorial plane. We propose that the stationarity of Pangea within a single hemisphere surrounded by subduction zones led to thermal isolation of the underlying asthenosphere and consequent heating as well as a large accumulation of hot plume material. We discuss some important implications of our analysis concerning the proposition that the succession of supercontinents and dispersed continents is controlled by an alternation from a degree 1 to a degree 2 planform.

Mantle plumes, triple junctions and transforms: A reinterpretation of Pacific Cretaceous – Tertiary LIPs and the Laramide connection

The Shatsky and Hess Rises, the Mid-Pacific Mountains and the Line Islands large igneous provinces (LIPs) present different challenges to conventional plume models. Resolving the genesis of these LIPs is important not only for a more complete understanding of mantle plumes and plume-generated magmatism, but also for establishing the role of subducted LIP conjugates in the evolution of the Laramide orogeny and other circum-Pacific orogenic events, which are related to the development of large porphyry systems. Given past difficulties in developing consistent geodynamic models for these LIPs, it is useful to consider whether viable alternative geodynamic scenarios may be provided by recent concepts such as melt channel networks and channel-associated lineaments, along with the “two mode” model of melt generation, where a deeply-sourced channel network is superimposed on the plume, evolving and adapting over millions of years. A plume may also interact with transform faults in close proximity to a mid ocean ridge, with the resultant bathymetric character strongly affected by the relative age difference of lithosphere across the fault.Our results suggest that the new two-mode melt models resolve key persistent issues associated with the Shatsky Rise and other LIPs and provide evidence for the existence of a conduit system within plumes that feed deeply-sourced material to the plume head, with flow maintained over considerable distances. The conduit system eventually breaks down during plume – ridge separation and may do so prior to the plume head being freed from the triple junction or spreading ridge. There is evidence for not only plume head capture by a triple junction but also for substantial deformation of the plume stem as the distance between the stem and anchored plume head increases. The evidence suggests that young transforms can serve as pathways for plume material migration, at least in certain plume head – transform configurations. A fortuitous similarity between the path of the Shatsky and Sio plumes, with respect to young spreading ridges and transforms, helps to clarify previously problematic bathymetric features that were not readily ascribed to fixed plumes alone. The Line Island Chain, which has been the subject of a vast number of models, is related mainly to several plumes that passed beneath the same region of oceanic crust, a relatively rare event that has resulted in LIP formation rather than a regular seamount track.Our findings have important implications for the timing and mechanism for the Laramide Orogeny in North America, demonstrating that the Hess Rise conjugate may be much smaller than traditionally thought. The Mid Pacific Mountains conjugate may not exist at all, given large parts of these LIPs were formed at an ‘off-ridge’ site. This needs to be taken into account while considering the effects of conjugate collision on mineralization and orogenic events.

Mantle Dynamics of the Central Atlantic Magmatic Province (CAMP): Constraints from Platinum Group, Gold and Lithophile Elements in Flood Basalts of Morocco

Abstract Mantle melting dynamics of the Central Atlantic Magmatic Province (CAMP) is constrained from new platinum group element (PGE), gold (Au), rare earth element (REE), and high field strength element (HFSE) data and geochemical modelling of flood basalts in Morocco. The PGE are enriched similarly to flood basalts of other large igneous provinces. The magmas did not experience sulphide saturation during fractionation and were therefore fertile. The CAMP is thus prospective for PGE and gold mineralization. The Pt/Pd ratio of the Moroccan lavas indicates that they originated by partial melting of the asthenospheric mantle, not the subcontinental lithospheric mantle. Mantle melting modelling of PGE, REE and HFSE suggests the following: (1) the mantle source for all the lavas was dominated by primitive mantle and invariably included a small proportion of recycled continental crust (<8%); (2) the mantle potential temperature was moderately elevated (c. 1430°C) relative to ambient mantle; (3) intra-lava unit compositional variations are probably a combined result of variable amounts of crust in the mantle source (heterogeneous source) and fractional crystallization; (4) mantle melting initially took place at depths between c. 110 and c. 55 km and became shallower with time (c. 110 to c. 32 km depth); (5) the melting region appears to have changed from triangular to columnar with time. These results are best explained by melting of asthenospheric mantle that was mixed with continental sediments during the assembly of Pangaea, then heated and further mixed by convection while insulated under the Pangaea supercontinent, and subsequently melted in multiple continental rift systems associated with the breakup of Pangaea. Most probably the CAMP volcanism was triggered by the arrival of a mantle plume, although plume material apparently was not contributing directly (chemically) to the magmas in Morocco, nor to many other areas of CAMP.

Simulation of Io’s plumes and Jupiter’s plasma torus

Io is a highly volcanic satellite of Jupiter. Its giant plumes rise hundreds of kilometers, creating large targets for incoming ions as Jupiter’s plasma torus overtakes Io in its orbit. Neutral material from Io’s sublimation atmosphere and volcanic plumes supplies the plasma torus, but the details of the interaction between neutral gas at Io and ions in the torus are not well understood. This paper suggests a process by which plume material is energized and ionized so as to supply the torus. We present three-dimensional direct simulation Monte Carlo simulations of giant plumes being bombarded by S+ and O+ ions which are moved based on precomputed electric and magnetic fields. The dependence of the plume/plasma interaction on the plume’s location on Io is investigated. The plume/plasma interaction is seen to be asymmetric even for a plume at the subplasma point because of the electric field that arises in an Io-fixed reference frame. Plasma is found to inflate and heat plume canopies and to give rise to a large, diffuse neutral cloud over the plume’s entire hemisphere. We also find that plasma can explain the thickness of red deposition rings observed on Io.

Dynamic characterization of the main Cantabrian river plumes by means of MODIS

River plumes formed in the Cantabrian coast of the Bay of Biscay constitute the main source of nutrients for this coastal area. They are able to sustain high levels of phytoplankton and primary productivity which, in turn, affect the associated ecosystems. Moreover, these plumes also influence other processes as stratification, flow circulation, transport of pollutants or erosion-sedimentation patterns, affecting the morphodynamical and biogeochemical characteristics of the area, which makes their study of high importance. The general small extension of these plumes makes necessary the use of high spatial and temporal resolution data to characterize their fine-spatial structure and to identify their evolution that happens at a short time scale. For that, the response of the Cantabrian plumes to the main forcing was analyzed by means of data provided by the Moderate Resolution Imaging Spectroradiometer sensor onboard Aqua and Terra satellites, which provides daily high resolution of up to 250 m. Composite images of Nalon, Pas-Besaya, Nervion and Adour plumes were created to analyze the effect of each forcing, including river discharge, wind and tides.Adour is the only Cantabrian plume formed even under low discharges due to the greater basin and river discharge. The rest of Cantabrian plumes are only well developed under high river discharges, which shows this forcing as the most important. Nalon, Pas-Besaya and Nervion plumes mainly influence eastward locations whereas Adour plume mainly affects areas located north of river mouth, due to the predominant currents in each area. Wind has a remarkable impact when plumes are well developed, being especially important in Nalon, Pas-Besaya and Nervion plumes. Plume material is dispersed to the ocean (under upwelling and seaward winds) or retained near coast (under downwelling and landward winds) attending to the main wind direction, conditioning the characteristics of the plume area. The semidiurnal tidal cycle is also important when plumes are developed, being all of them greater under low tidal conditions, although the impact is less important in the Adour plume. The higher stability of Adour plume to the forcing could be related to the much greater extension, which makes necessary stronger forcing to cause similar effects. On the other hand, this greater extension favors its impact on thermohaline properties of seawater. The Adour River is able to provoke winter stratification in the plume area, as well as thermal inversions, which condition the thermohaline properties respect to oceanic area not affected by the plume.By last, the influence of Cantabrian plumes on the annual cycle of chlorophyll was evaluated for each plume area and the adjacent ocean also by means of MODIS data. A chlorophyll peak was detected in both areas for early spring and high values of chlorophyll were also detected during autumn and winter but only in plume areas, associated to the input of nutrients and the haline stratification promoted by the high rivers discharges during these months.