Increasing Spreading Rate Research Articles

Effects of Wind on Heat Transfer and Spread of Different Fire Lines Across a Pine Needle Fuel Bed

ABSTRACT In this work, a series of surface fire experiments are performed to investigate the effect of wind velocity on the surface fire behaviors over a pine needle fuel bed under nine wind velocities (0/0.25/0.5/0.75/1/1.5/2/2.5/3 m/s) and three fuel loads (0.2/0.5/0.8 kg/m2). The essential parameters are obtained and analyzed, including flame length, flame angle, flame spread rate, and heat flux. The main valuable conclusions have been drawn: (1) Under no or low wind velocity, the flame tilts in the direction of the burned fuel, and the fire line shows a linear shape; whereas as the wind velocity increases, the flame gradually shifts toward the unburned fuel and the fire line is observed to be curved. (2) Flame angle decreases with increasing wind velocity and is not sensitive to fuel load, while flame length, heat transfer, and fire spread rate increase with increasing wind velocity and fuel load. Moreover, the empirical flame length and fire spread rate models are proposed considering the wind velocity and fuel load. (3) The modified model of radiation heat flux for surface fire spread under wind conditions taking different fire line shapes into account, is developed, and the predicted values are in good agreement with the experimental data. This paper’s results can help better understand the fire spread and controlling mechanism of surface fire under wind velocity conditions.

Tectonically assisted emplacement of oceanic intraplate volcanoes: The Bathymetrists Seamounts, central Atlantic

The origin of broad intraplate volcanic provinces has been related to deep mantle plumes or shallow lithospheric processes, e.g., underlying large fault systems. One example of an understudied intraplate volcanic province is the Bathymetrists Seamounts (BSM) in the central-eastern Atlantic, an area with dense and extended fracture zones, but the BSM has been associated with a mantle plume origin. Extensive bathymetric mapping and seafloor sampling show that most BSM-seamounts resemble flat-topped guyots capped by carbonate platforms. Vesicular, volcanoclastic samples imply that their tops formed near sea level, followed by reef formation during cessation of volcanism and crustal subsidence. Erosion determines the seamount irregularity proportional to their sizes. Strong ellipticity of some seamounts is related to multiple vents that erupted along fractures. The orientation of the volcanoes, carbonate platforms, and morphological lineaments of the BSM show particular trends that reveal information on their origin and formation mechanisms. Geomorphological analyses indicate a structural control on volcano emplacement related to underlying lithospheric faults resembling a Riedel shear pattern. The stress field corresponding to their orientations is related to a NE-SW tensional setting, fitting to the prevalent tectonic setting ~56–38 Ma years ago that coincides with the BSM formation and an increase in spreading rates. A change in movement of the African plate during this time, together with the reactivation of fracture zones of the strongly sheared equatorial Atlantic, created pathways in the lithosphere and possibly enhanced magmatism. The seamounts do not show distinct differences in erosion state, morphology, carbonate platform depth, or Mn-crust thickness, in contrast to what would be expected for an age progression within the seamount chain. Our observations, therefore, do not support a plume mantle source. While the magmatic source remains undefined, we show that tectonic pathways determined the shape of the seamounts and enabled the broad emplacement of the Bathymetrists seamount chain.

Oxidation and wetting characteristics of lead-free Sn-0.7Cu solder alloys with the addition of Fe and Bi

In this paper, the oxidation and wetting behaviour of Sn-0.7Cu and Sn-0.7Cu-0.05Fe-2Bi solder alloys has been investigated. The alloys were subjected to 200 °C in oxygen rich environment. Weight gain curves reveal that the oxidation behaviour obey the parabolic rate law. X-Ray photo electron spectroscopy (XPS) reveals the presence of SnO and SnO2 oxide layer on the surface of Sn-0.7Cu solder alloys. SnO was formed as the basic oxide layer. However, at higher temperature SnO transforms into SnO2. Addition of Bi results in the formation of Bi2O3. The Pilling-Bedworth ratio of SnO, SnO2 and Bi2O3 oxides are 1.28, 1.35 and 1.23 respectively. These ratios confirm the passive nature of oxide layers. Wetting behaviour of Sn-0.7Cu and Sn-0.7Cu-0.05Fe-2Bi were investigated on Cu substrate. The addition of Bi and Fe improves the wetting properties of Sn-0.7Cu solder alloys. Alloying with Bi and Fe results in growth suppression of intermetallic compound at the interface. Increase in spreading rate, decrease in wetting angle and solder height reveals better performance of the Sn-0.7Cu-0.05Fe-2Bi solder alloy.

Antimicrobial and anti-biofilm activities of polyphenols extracted from different Saudi Arabian date cultivars against human pathogens

BackgroundMicrobial diseases have emerged as a serious threat to the healthcare system globally and also in Saudi Arabia; various diseases are associated with higher mortality and increased spreading rates. Dietary sources are often entertained to improve the immune system of the body to fight against these infections. The date fruit (Phoenix dactylifera L) is one such functional food that is less explored for its actual potentials. MethodsThe polyphenols isolated from the different cultivars of dates in Saudi Arabia (Ajwa, Safawi, Khalas, and Sukkary) was evaluated for their antibacterial, anti-fungal and anti-biofilm forming abilities. The anti-radical properties of the phenolic extract were conducted in terms of the scavenging of diphenyl-1-picrylhydrazyl radical, hydrogen peroxide radicals and ABTS radicals. The anti-inflammatory potential was analyzed in terms of lipoxygenase activity inhibition. ResultsThe phenolic compounds of different dates were spectrophotometrically estimated and cultivars such as Ajwa and Sukkary had the highest polyphenol content. It was also noteworthy that they exerted potent antibacterial activities against Staphylococcus aureus, Streptococcus pyogenes, and Pseudomonas aeruginosa as estimated by the least minimal inhibitory concentration (MIC) or minimal bactericidal concentration (MBC) values. Besides, these polyphenols reduced the biofilm formation by these bacterial pathogens; it is thus possible that the polyphenols from dates can be a promising antimicrobial agent against various pathogenic strains. Corroborating with these, the polyphenol extracts from different Saudi Arabian dates were found to inhibit the growth of mycelium in strains of Candida albicans and Aspergillus niger. Apart from these, the polyphenol isolates also exhibited significant anti-radical properties against different reactive radical systems. ConclusionOverall, the efficacy of phenolic compounds extracted from the dried date fruits are not only restricted to the functional food features; instead, these molecules are capable of preventing the growth of microbial pathogens of humans. Hence, it may emerge as potent antibacterial, anti-fungal and anti-biofilm forming candidates.

Numerical study of flame spread in a narrow flow duct in microgravity – effects of flow confinement and radiation reflection

A three-dimensional numerical study is performed to investigate concurrent-flow flame spread over thin solid fuels in microgravity. The model considers the burning scenarios of a recently concluded ISS microgravity experiment, Confined Combustion. Cellulose based thin samples are burned in a small flow duct. The height of the flow duct and the radiation reflectance of the duct wall are varied. Flame development and steady spread flame characteristics are compared with the experimental results at various duct heights. The numerical results demonstrate that the confinement imposed by the duct walls accelerates the flow during the combustion thermal expansion, enhancing the conductive heat transfer to the solid samples. When the duct height is below a critical height, the flow confinement limits oxygen supply to the flame, and the duct wall acts as a conductive heat sink. As a result of the interplay of these effects, the flame spread rate and pyrolysis length first increase and then decrease as the duct height decreases. Eventually, the flame fails to spread at a quenching duct height. In addition, side-leading concave (two-teeth fork shaped) flames are observed below the critical duct height. This flame shape increases the flame surface area and facilitates oxygen transport to the combustion zone. When the duct wall reflectance varies, a higher reflectance yields a longer pyrolysis length and a faster spread rate. This is due to enhanced heat input to both the solid sample surface and the gaseous flame. This effect is most significant for medium duct heights. At large duct heights, the duct wall is far from the flame and the sample. At small duct heights, while flame spread rate increases with the wall reflectance, the pyrolysis and flame length remain similar as combustion is limited by oxygen supply.

OIL PRICE BEHAVIOUR, EXCHANGE RATE MOVEMENT AND THE COVID-19 PANDEMIC IN NIGERIA: ANALYSIS OF THE FIRST THREE QUARTERS OF 2020

This paper evaluates the response of oil price and exchange rate to the corona virus pandemic shock aside from the link between oil price and exchange rate for the first three quarters of 2020 in Nigeria. The theoretical framework emanates from the informal approach and the terms of trade channels. Using VAR cointegration approach, results show existence of long run relationship among the oil price, exchange rate movement and the corona virus indicators based on Max-Eigen and Trace test statistic. End of first quarter oil price, discharge rate and fatality rate negatively relate with current exchange rate. First quarter exchange rate and fatality rate positively relates to oil price behaviour in the third quarter while end of first quarter discharge rate increase fosters oil price decline. First quarter spread rate increase gradually reduces oil demand and the price in the third quarter. All corona virus indicators and exchange rate variable Granger Cause current oil price. Diversification is key to widen export base and increase foreign exchange and stability. Policy measures to sustain the economy in the post COVID-19 and beyond are necessary for long term development.

Factors influencing the development of violent pyroconvection. Part II: fire geometry and intensity

Fire spread associated with violent pyrogenic convection is highly unpredictable and difficult to suppress. Wildfire-driven convection may generate cumulonimbus (storm) clouds, also known as pyrocumulonimbus (pyroCb). Research into such phenomena has tended to treat the fire on the surface and convection in the atmosphere above as separate processes. We used a numerical model to examine the effect of fire geometry on the height of a pyroconvective plume, using idealised model runs in a neutral atmosphere. The role of geometry was investigated because large areal fires have been associated with the development of pyroCb. Complementary results (detailed in Part I) are extended by considering the effect that fire shape can have on plume height by comparing circular, square, and rectangular fires of varying length and width, representing the difference between firelines and areal fires. Results reveal that the perimeter/area ratio influenced the amount of entrainment that the plume experiences and therefore the height to which the plume rises before it loses buoyancy. These results will aid in the prediction of blow-up fires (whereby a fire exhibits a rapid increase in rate of spread or rate of spread) and may therefore be useful in determining where fire agencies deploy their limited resources.

Correlations between oceanic crustal thickness, melt volume, and spreading rate from global gravity observation

Oceanic crustal accretion at mid-ocean ridges is a function of spreading rate, mantle temperature, and composition, which are intertwined in affecting melt production and oceanic crustal thickness. Sparse and irregular seismic and geochemical observations on a global scale showed no correlation between crustal thickness and spreading rate along slow to fast-spreading centers. Here, we compile a global oceanic crustal thickness model from gravity data to revisit this issue at a high resolution. Gravity-observed melt volume shows a positive correlation with spreading rate globally, implying that spreading rate is the dominant factor in melt production. However, oceanic crustal thickness is negatively correlated with spreading rate from slow to fast-spreading centers, and this trend is further consolidated by the increase in Curie point depth (a geothermal proxy) and ridge depth with increasing spreading rate. Thus, a decreasing near-ridge temperature probably contributes to crustal thinning from slow to fast-spreading centers. Inferred low melt volume anomalies beneath fast-spreading centers are consistent with a 20 °C temperature drop in the near-ridge mantle, likely caused by efficient hydrothermal cooling.

Controls on the magmatic fraction of extension at mid-ocean ridges

The fraction M of plate separation accommodated by magma emplacement at mid-ocean ridges has been recognized as the main control on seafloor spreading modes, yet the factors that control M itself are poorly understood. Here we put forward a simple theoretical framework explaining M in terms of short-term cycles of earthquakes and dike intrusions interacting with one another by modulating the stress state of the ridge axis. Axial lithospheric thickness and the rate of pressure build-up in shallow, replenishing magma sills are the two main parameters controlling M in our simulations. Combined with plausible scenarios for the increase of pressure build-up rate and the decrease of lithospheric thickness with increasing spreading rate, our model appropriately brackets available measurements of M from slow, intermediate, and fast-spreading ridges. Our model further suggests that the transitions between major modes of seafloor spreading (detachment faulting, symmetric faulting, and fully-magmatic) correspond to thresholds in axial lithospheric thickness, and that the great variability in M at slow and ultraslow ridges directly reflects along-axis variability in thermal structure. More generally, this implies that the balance between bottom-up magmatic heating and top-down hydrothermal cooling fully determines the time-averaged rate of magmatic intrusions in the brittle lithosphere, and thus the modes of mid-ocean ridge faulting which shape ∼2/3 of Earth's surface.

Moisture absorption and drying alter nonadditive litter flammability in a mixed conifer forest

Abstract Moisture content is a strong determinant of forest fuel flammability. However, little is known about the mechanisms by which species‐specific litter traits influence litter moisture absorption and retention. Characterizing how litter fuels retain moisture through time and how fuels from multiple species interact are key steps to adding taxon‐specific information to fire behaviour prediction. To fill these gaps in knowledge, we determined moisture absorption and retention characteristics of the litter from multiple tree species, investigated what litter traits influenced these processes and tested for nonadditive moisture dynamics and nonadditive flammability in multi‐species mixtures. The litter from eight tree species of a mixed conifer forest was saturated and allowed to dry to determine moisture absorption capacity and drying rates. Burn trials were performed in litter beds of single species and of mixtures to establish flammability response to the dry‐down process and to species interactions. Litter mixtures exhibited nonadditivity in flame spread rate and in fuel consumption. This nonadditivity became more positive with fuel drying. Moisture dynamics varied across species with higher specific leaf area being associated with higher maximum absorption and lower litter bulk density being associated with faster drying rates. We found that these differing moisture dynamics resulted in time since wetting having strongly differing effects on flammability across the major litter types typified by different tree taxa. Synthesis. This study is the first to examine ecologically relevant drying rates and their interaction with nonadditive mixture effects on flammability. We find that taxon specific patterns of moisture absorption and drying change flammability rankings under moist compared with dry fuels because traits that increase flame spread rate increase water absorption. Litter mixtures generally burn with fire behaviour more similar to that of the most flammable constituent species and this effect increases as fuels dry.

Numerical study on opposed-flow flame spread over discrete fuels – The influence of gap size and opposed-flow velocity

Flame spread over solid fuel is a common phenomenon in fire scenes. This work looks into the relationship between the flame spread and the gap length between fuel beds at different opposed-flow velocities. An unsteady numerical model is developed to study the opposed-flow flame spread over discrete fuels. The influence of the gap size between the discrete fuels and the opposed-flow velocity on the opposed-flow flame spread is investigated, and the results are validated with an analytical model. The characteristics of solid burning, gas fuel and flame spread rates are examined. The results of temperature and gas fuel distribution show that the heat transfer from the flame to the discrete fuels decreases as the gap size increase. The pyrolysis front lags behind the leading position of gas thermal structure because the discrete fuels behind the flame front can provide fuel gas to the flame front by diffusion for combustion. The mass diffusion plays a significant role in the flame spread across the gaps. The average flame spread rate increase first and then decreases with the increase of gap size, because of the competition mechanism between the flame jump effect and the heat transfer. Besides, the flame cannot spread across to the next discrete fuel if the gap size increases to a critical value. The analytical and numerical results showed that the critical gap size is proportional to the reciprocal of opposed-flow. This work should be significant to predict the fire growth of discrete fuels and its potential hazards.

Data-driven modelling and prediction of COVID-19 infection in India and correlation analysis of the virus transmission with socio-economic factors

AimsThe current study attempts to model the COVID-19 outbreak in India, USA, China, Japan, Italy, Iran, Canada and Germany. The interactions of coronavirus transmission with socio-economic factors in India using the multivariate approach were also investigated. MethodsActual cumulative infected population data from 15 February to May 15, 2020 was used for determination of parameters of a nested exponential statistical model, which were further employed for the prediction of infection. Correlation and Principal component analysis provided the relationships of coronavirus spread with socio-economic factors of different states of India using the Rstudio software. ResultsCumulative infection and spreadability rate predicted by the model was in good agreement with the actual observed data for all countries (R2 = 0.985121 to 0.999635, and MD = 1.2–7.76%) except Iran (R2 = 0.996316, and MD = 18.38%). Currently, the infection rate in India follows an upward trajectory, while other countries show a downward trend. The model claims that India is likely to witness an increased spreading rate of COVID-19 in June and July. Moreover, the flattening of the cumulative infected population is expected to be obtained in October infecting more than 12 lakhs people. Indian states with higher population were more susceptible to virus infection. ConclusionsA long-term prediction of cumulative cases, spreadability rate, pandemic peak of COVID-19 was made for India. Prediction provided by the model considering most recent data is useful for making appropriate interventions to deal with the rapidly emerging pandemic.

Review of the Transition From Smouldering to Flaming Combustion in Wildfires

Wildfires are the occurrence of uncontrolled combustion in the natural environment (forest, grassland, or peatland). The frequency and size of these fires are expected to increase globally due to climate change, land use, and population movement, posing a significant threat to populations living at the wildland urban interface (WUI), as well as to habitats and the environment. Wildfires can be broadly divided into two types, smouldering (heterogeneous combustion) and flaming (homogeneous combustion). Both are important in wildfires and despite being characteristically different, one can lead to the other. The smouldering-to-flaming (STF) transition is considered threatening because it represents a sudden increase in spread rate, power, and hazard. STF transition is a sudden initiation of homogeneous gas-phase ignition preceded by smouldering combustion, and needs sufficient oxygen supply, thermal energy production, and pyrolysis products. Its unpredictable occurrence, temporally and spatially, poses an additional challenge in wildfire prevention and mitigation. For example, flaming fire may reignite through the STF transition of an undetected smouldering fire, or the transition from ember. The current understanding of the mechanisms leading to the transition is poor. Strong oxidation of char is a plausible mechanism due to its high exothermicity, acting both as heat source in driving gaseous fuel production and ignition source of the gaseous fuel. Broadly, the literature has identified two variables that govern the STF transition, i.e. oxygen supply and heat flux, on samples ranging from 0.1 to 1.22 m. Airflow velocity has competing effects. It increases oxygen supply to the reaction zone, thus increasing the reaction rate of oxygen-limited spread, but simultaneously increases convective cooling. Permeability of a fuels and fuel ability to remain consolidated (maintain its integrity) during burning influences the propagation of smouldering. Permeability controls the oxygen penetration into the fuel, and consolidation allows the formation of internal pores where STF can take place. Considering the high complexity of the STF transition problem, more studies are needed on different types of fuel, especially on wildland fuels. This review synthesizes the research and identifies regions for further research as well as informs on various STF transition mechanisms in the literature.

Experimental study on the effects of width and self-extinguishing on the upward flame spread for linen fabric

Linen fabric has been widely applied to interior decoration, medical and health care, industrial fabrics and oil painting exhibitions due to its advantages of good hygroscopicity, strong air permeability, excellent health care functions. In this paper, a series of comparative experiments were performed to study the effects of sample width on upward flame spreading using linen fabric with various widths ranging from 4 to 8 cm and length of 1.6 m. The major conclusions are summarized as follows: when sample width is 4 cm or 5 cm, the upward spreading process can be divided into three typical stages: two-sided flame accelerated spread, one-sided flame self-extinguishing and one-sided flame stable spread. Whereas for samples with a width larger than 5 cm, the upward flame spreading only exhibits the two-sided flame accelerated spread stage. Moreover, the maximum pyrolysis height, steady pyrolysis height, maximum spread rate and steady spread rate increase with sample width. The relationship between maximum spread rate and sample width can be described by a power-law function. Furthermore, after the one-sided flame self-extinguishing occurs, the pyrolysis height and spread rate decrease dramatically, which can be explained using energy conservation. The ratio of pyrolysis length before and after the self-extinguishing is about 2.0, and the corresponding ratio of spread rate is also around 2.0.

Combustion behaviour and dominant shrinkage mechanism of flexible polyurethane foam in the cone calorimeter test.

The shrinkage is an important thermal response of flexible polyurethane foam (FPUF) in fire, which couples its first combustion stage and influences the initial fire spread. In this paper the combustion and shrinkage behaviours are quantitatively investigated and the shrinkage mechanisms are discussed. The critical heat flux for the shrinkage is about 13 kW/m2, between the critical heat flux for piloted ignition and that for non-piloted ignition. Above the critical value the shrinkage rate increases linearly with increasing the heat flux. As the foam density decreases both the shrinkage rate and the first peak of Figra curve which reflects the initial fire spread rate increase. The perceptible shrinkage originates from the decomposition via which the struts convert to the melts. Both the shrinking of struts and the gasification play a minor role. The collapse of porous structure, namely the melts filling into the pores to form the tar layer, dominates the shrinkage. The tar is composed of polyols produced after the first decomposition stage. Beneath the tar layer the porous structure is unchanged. To reduce the fire hazards of FPUF by its heat insulation merit it needs to maintain the porous structure at the first decomposition stage.

Breakup volcanism and plate tectonics in the NW Atlantic

Passive margins are the locus of tectonic and magmatic processes leading to the formation of highly variable along-strike and conjugate margins structures. Using extensive new seismic, gravity, and magnetic datasets, complemented by seabed samples and field work, we investigate the tectonomagmatic evolution of the northwest (NW) Atlantic where breakup-related igneous rocks were emplaced during several Paleogene events associated with lithospheric stretching, continental breakup, and the formation of new oceanic basins. Interpretational methods include integrated seismic-gravity-magnetic (SGM) interpretation and seismic volcanostratigraphy. In addition, seabed and field samples were collected and analyzed to constrain the basin stratigraphy, hydrocarbon potential, and the geochronology and geochemistry of the volcanic sequences. Offshore, 2D seismic data reveal several Seaward Dipping Reflector (SDR) wedges and escarpments in the Labrador Sea, Davis Strait, and Baffin Bay. Onshore, eastward prograding foreset-bedded hyaloclastite delta deposits and overlying horizontal lava successions outcrop on Nuussuaq. These hyaloclastites and lava successions are world class analogues to the Lava Delta and Landward Flows volcanic seismic facies units identified offshore. Our mapping results document an aerial extent of the Paleogene breakup-related volcanics of 0.3 × 106 km2, with an estimated volume of 0.5–0.6 × 106 km3. Basalt samples recovered by dredging the Upernavik Escarpment have late Paleocene to/early Eocene ages, whereas the sedimentary samples provide an excellent seismic tie with the stratigraphy and the geology in this frontier area. From the integrated SGM interpretation, we identify a rapidly thinning crust and changes in top and intra-basement seismic reflection characteristics in the oceanic domain correlated with transition between different magnetic domains. The mapping results were subsequently integrated in a plate tectonic model. The plate tectonic reconstruction and basalt geochronology suggest that the majority of the volcanism in the NW Atlantic occurred between ~62 and ~58 Ma, associated with an increased spreading rate in the Labrador Sea, starting from the onset of the Selandian (~61.6 Ma). A change in the spreading direction during the Eocene (~56 Ma), synchronously with a shift of volcanic activity from the NW to the NE Atlantic, correspond to a northward drift of Greenland and the initiation of the Eurekan Orogeny. Finally, our interpretations reveal a complex rift configuration along the NW Atlantic conjugate margins both prior to and during breakup.

Oblique seafloor spreading across intermediate and superfast spreading centers

We show that oblique seafloor spreading occurs in several regions where obliquity, α, was not recognized before. These include the slow spreading centers of the Red Sea (α≈20°), intermediate spreading centers of the Cocos–Nazca plate boundary between 91°W and 94°W (α≈9°), and superfast spreading centers of the East Pacific Rise at the Nazca–Pacific plate boundary between 29°S and 32°S (α≈10°) and perhaps between ≈16°S and ≈22°S (α≈4°). Thus, oblique spreading occurs across slow, intermediate, and superfast spreading centers, but not across fast spreading centers. Across intermediate and superfast spreading centers, oblique spreading does not occur in staircase-mode plate geometries, but does occur in oblique-mode plate geometries. Across slow and intermediate spreading centers, obliquity tends to decrease with increasing spreading rate, while across fast and superfast spreading centers it tends to increase with increasing spreading rate. Oblique spreading at intermediate and superfast spreading centers may be related to magma overpressure or to unusual directions of remote tectonic stress or to ongoing plate boundary reorganizations or to some combination of these. Using prior methods, we estimate the ratio of overpressure to remote tectonic stress for several spreading centers. In particular we show along a segment of the Cocos–Pacific plate boundary that magma overpressure is only one-fourth as large as remote tectonic stress, consistent with a prior inference from other observations. The highest obliquity occurs along ridge segments lying 200 km to 1500 km from a mantle plume, but not all ridge segments near plumes spread obliquely. For one set of estimates of plume fluxes, the rate of plume flux delivered to ridges correlates positively and significantly with spreading rate.

The influence of spreading rate, basement composition, fluid chemistry and chimney morphology on the formation of gold-rich SMS deposits at slow and ultraslow mid-ocean ridges

Seafloor massive sulphide (SMS) deposits are variably enriched in precious metals including gold. However, the processes invoked to explain the formation of auriferous deposits do not typically apply to mid-ocean ridge settings. Here, we show a statistically significant, negative correlation between the average gold concentration of SMS deposits with spreading rate, at non-sedimented mid-ocean ridges. Deposits located at slow spreading ridges (20–40 mm/a) have average gold concentrations of between 850 and 1600 ppb; however, with increasing spreading rate (up to 140 mm/a), gold concentrations gradually decrease to between ~ 50 and 150 ppb. This correlation of gold content with spreading rate may be controlled by the degree and duration of fluid-rock interaction, which is a function of the heat flux, crustal structure (faulting) and the permeability of the source rocks. Deposits at ultraslow ridges, including ultramafic-hosted deposits, are particularly enriched in gold. This is attributed to the higher permeability of the ultramafic source rocks achieved by serpentinisation and the inherent porosity of serpentine minerals, combined with relatively high gold concentrations in peridotite compared with mid-ocean ridge basalt. Variations in fluid chemistry, such as reducing conditions and the potential for increased sulphur availability at ultramafic-hosted sites, may also contribute to the high concentrations observed. Beehive chimneys, which offer more favourable conditions for gold precipitation, may be more prevalent at ultramafic-hosted sites due to diffuse low-velocity venting compared with more focussed venting at basalt-hosted sites.

Seamounts and oceanic igneous features in the NE Atlantic: a link between plate motions and mantle dynamics

Abstract A new regional compilation of seamount-like oceanic igneous features (SOIFs) in the NE Atlantic points to three distinct oceanic areas of abundant seamount clusters. Seamounts on oceanic crust dated 54–50 Ma are formed on smooth oceanic basement, which resulted from high spreading rates and magmatic productivity enhanced by higher than usual mantle plume activity. Late Eocene–Early Miocene SOIF clusters are located close to newly formed tectonic features on rough oceanic crust in the Irminger, Iceland and Norway basins, reflecting an unstable tectonic regime prone to local readjustments of mid-ocean ridge and fracture zone segments accompanied by extra igneous activity. A SOIF population observed on Mid-Miocene–Present rough oceanic basement in the Greenland and Lofoten basins, and on conjugate Kolbeinsey Ridge flanks, coincides with an increase in spreading rate and magmatic productivity. We suggest that both tectonic/kinematic and magmatic triggers produced Mid-Miocene–Present SOIFs, but the Early Miocene westwards ridge relocation may have played a role in delaying SOIF formation south of the Jan Mayen Fracture Zone. We conclude that Iceland plume episodic activity combined with regional changes in relative plate motion led to local mid-ocean ridge readjustments, which enhanced the likelihood of seamount formation. Supplementary material: Figures detailing NE Atlantic seamounts and SOIF distribution, and the location of earthquake epicentres are available at https://doi.org/10.6084/m9.figshare.c.3459729

Tectonic activity evolution of the Scotia‐Antarctic Plate boundary from mass transport deposit analysis

AbstractThe spatial distribution and temporal occurrence of mass transport deposits (MTDs) in the sedimentary infill of basins and submerged banks near the Scotia‐Antarctic plate boundary allowed us to decode the evolution of the tectonic activity of the relevant structures in the region from the Oligocene to present day. The 1020 MTDs identified in the available data set of multichannel seismic reflection profiles in the region are subdivided according to the geographic and chronological distributions of these features. Their spatial distribution reveals a preferential location along the eastern margins of the eastern basins. This reflects local deformation due to the evolution of the Scotia‐Antarctic transcurrent plate boundary and the impact of oceanic spreading along the East Scotia Ridge (ESR). The vertical distribution of the MTDs in the sedimentary record evidences intensified regional tectonic deformation from the middle Miocene to Quaternary. Intensified deformation started at about 15 Ma, when the ESR progressively replaces the West Scotia Ridge (WSR) as the main oceanic spreading center in the Scotia Sea. Coevally with the WSR demise at about 6.5 Ma, increased spreading rates of the ESR and numerous MTDs were formed. The high frequency of MTDs during the Pliocene, mainly along the western basins, is also related to greater tectonic activity due to uplift of the Shackleton Fracture Zone by tectonic inversion and extinction of the Antarctic‐Phoenix Ridge and involved changes at late Pliocene. The presence of MTDs in the southern Scotia Sea basins is a relevant indicator of the interplay between sedimentary instability and regional tectonics.