Mobility Of Chemical Elements Research Articles

Integrated geochemical analysis of urban and peri-urban soils: a case study of Lamia City, Greece.

The occurrence of Potentially Toxic Elements (PTEs) and other chemical elements in urban and peri-urban soils impacts human health and quality of life, posing a challenge for geoscientists. This study investigated the soil geochemistry of Lamia City, focusing on identifying the geogenic and anthropogenic origins of elements. A total of 168 topsoil samples (0-10cm) were collected in April 2023, and the analysis included the near-total concentrations of 51 elements. Descriptive, correlation, multivariate statistics (i.e., Factor Analysis-FA and Hierarchical Cluster Analysis-HCA), Geographic Information Systems (GIS) mapping, and mineralogical analysis were employed to identify potential element sources. The results indicated that the elements in soils originated from geogenic, anthropogenic, and mixed sources. Geogenic origins are associated with ultramafic rocks (e.g., Mg, Cr, Ni, Co, Fe, Sc, Mn), carbonate rocks (e.g., Ca, Sr), and Quaternary sediments (e.g., K, Na, Ba, Tl, Be, Rb, Ti, V, Ga, and Rare Earth Elements-REEs); associations are linked to specific identified minerals. All applied statistical analyses reveal that the mobility of chemical elements in the urban and peri-urban soils of Lamia city is primarily affected by geochemical processes such as element substitution, chemical weathering, pedogenesis, adsorption, precipitation, evaporation, and organic matter presence. The P, Ag, Hg, Pb, Sn, Zn, Sb, Cd, Cu, and U were associated with anthropogenic influences, particularly in areas with high population density, heavy vehicle traffic, and intensive agricultural practices. Additionally, some elements (e.g., Ca, Cd, Cu, Mo, Mn, and Li) exhibited mixed origins. This integrated approach offers valuable insights into the spatial distribution and sources of PTEs in urban and peri-urban environments, providing critical information for environmental management and public health protection strategies.

Using Soil Magnetic Susceptibility Proxies to Estimate Overburden Thickness Overlying Ore of Lateritic Soils in Sulawesi Island Indonesia

Sulawesi Island is one of the largest Ni ore producers in Indonesia. It is also expected to be a significant potential source of some critical metals (e.g., Co, Sc, rare-earth elements, and platinum-group elements). However, few studies show the post-mining impact on some heavy metal elements concentrated in this area. Therefore, improving the efficiency and effectiveness of soil organization and its effect on soil reclamation after mining is helpful. This study aimed to determine the accuracy in estimating the thickness of the overburden covering the nickel ore body profile from lateritic nickel post-mining areas by magnetic susceptibility measurements to discrepancy the overall laterite horizon, whereas χLF and χFD are used to distinguish the overburden zona and limonite and saprolite zone. The lateritic profile studied consists of soil formation of Fe-rich material in the Morowali, and Pomalaa block. We also evaluated the chemical element content of the soil and understood the relationship between the magnetic and geochemical properties of the soil. This study reveals the superparamagnetic (SP)-enriched soils indicated with the increase of the FD% values into the upward horizon, where the maximum values of FD are generally found at ranges 1 to 4m, indicating the overburden layers. Meanwhile, in the depth of 4m to 6m, the values of FD vary only slightly in the lower part initiated by the limonite layers, and then > 6m decreases sharply to the bottom, indicating the saprolite layers. The chemical element mobility trends indicate that Fe, Co, Cr, Mn, and Ti increase toward the layers, which is the same pattern as in FD. Due to this, parameters magnetics may also be a new geophysical approach for estimating the distribution of economically valued minerals on lateritic soils. The strong correlation of Co with Fe, Mn, and Cr in all layers indicates the influence of weathering o n these ultramafic rocks. This suggests an increasing trend toward prolonged pedogenesis.

Hydrochemical Anomalies in the Vicinity of the Abandoned Molybdenum Ores Processing Tailings in a Permafrost Region (Shahtama, Transbaikal Region)

The mobility of chemical elements during the transition from molybdenum ore processing waste to aqueous solutions and the hydrochemical anomalies of a number of elements in surface and underground waters in the vicinity of an abandoned tailings dump were investigated. It is shown that alkaline and alkaline earth metals have high mobility—the main rock-forming components (sodium, lithium, magnesium, strontium), which are released into solution due to leaching from the minerals of the host rocks, as well as metals with zinc, cadmium, manganese, and nickel, which are released into solution due to the dissolution of ore sulfides. Elements with high mobility include Sb, Co, Cu, Be, Se, and Tl. Medium mobility has As, an element of the first hazard class, as well as Mo, Fe, and Pb. Hydrochemical anomalies of cadmium, arsenic, molybdenum, and lead have been determined. The nature of the arsenic and molybdenum anomalies is most likely related to the regional background, while the source of cadmium and lead is most likely the waste studied. The main chemical forms of the presence of elements in the solution of ponds on the surface of tailings ponds are free-ion and sulfate complexes. For example, in the samples of the Shakhtama River and groundwater, we found carbonate, bicarbonate, and hydroxide complexes. The information obtained should be taken into account when planning measures for the purification of surface and groundwater from metals. Additional studies should consider using groundwater in the vicinity of the tailings for drinking water supply.

Hydrogeochemistry and stable isotopes of groundwater in the Sudano-Sahelian zone: A case of the Mayo Bocki watershed in North Cameroon

Groundwater is the main source of water supply for domestic, agricultural and industrial uses, especially in the sahelian regions. The present study is carried out in the basement aquifers of the Mayo Bocki catchment, Cameroon. It aims to determine the controlling factors of groundwater mineralization and to assess the relative mobility of chemical elements in the aquifers. The methodology adopted was based on conventional geochemical classifications and multivariate statistical analyses. The results revealed that these waters are characterised by low to medium mineralization in both the altered and fractured aquifers. The average concentration of cations followed the trend Ca2+ > Na+ > Mg2+ > K+ while that of anions was HCO3− > NO3− > Cl− > SO42−. The predominant hydrochemical facies was Ca Mg- HCO3 (77%). The acquisition of mineralization by groundwater in this basin involves several natural geochemical processes, including hydrolysis of silicates, dissolution of carbonate minerals, base exchange and leaching. In addition, the chemical inputs used in agriculture make a significant contribution to the chemical signature of these waters. Stable isotopes (18O, 2H) have shown that the water masses in the reservoirs are derived from rainwater and that their chemistry is not influenced by evaporation process. The predominant chemical alteration type in the area under study is monosiallitization. During this weathering process, the behaviour of chemical elements varies from one rock to another. In general, altered rock forms (granite, basalt, trachyte, schist and clay) are enriched in K2O, Na2O, P2O5, Al2O3, SiO2 and depleted in CaO, MgO, MnO, F2O3, SO3, Cl. The relative mobility of the constituents in the aqueous phase revealed that Mn, Zn, Sr, Ca, Na and Mo are the most mobile elements while Al, Th, Cs, Fe are the least mobile elements.

From rock to soil: Elemental mobility during pedogenesis in a deep Ultisol profile at the Mantiqueira Mountain Range, Southeastern Brazil

A better understanding of the mobility of chemical elements during weathering and leaching processes requires the complete analysis of soil profiles down to the bedrock, especially in tropical environments, due to the great thickness of the weathering mantle. We studied a deep profile comprising solum, saprolite and rock at the Mantiqueira Mountain Range in Brazil aiming to assess the mobility of major and trace elements in an Ultisol and its parent rock (gneiss). A 63-m borehole was drilled from the topsoil down to the gneiss. Samples from the solum (A + B horizons), saprolite and gneiss were collected and analyzed for chemical, physical and mineralogical attributes and elemental contents. A mass balance equation was applied to quantify the net result of weathering considering Ti as the most stable element. Despite the steep relief, a very deep soil profile was found (24-m solum + saprolite). Alkaline and alkaline earth metals (e.g., Ca, K, Sr, Rb and Ba) and Mn were strongly depleted in the solum and saprolite. Al, Fe, Zn, P, Zr, Y and V showed residual enrichment in the saprolite, while Al and Zr revealed enrichment in the transformation from saprolite to solum. Biggest changes were observed in the rock/saprolite interface, not in saprolite/solum. The efficient drainage of this soil might be related to the weathering of the saprolite. Variations of elemental contents from the soil surface down to the parent rock helped to elucidate the changes of elemental contents caused by the weathering and leaching processes.

Concentration and mobility of trace elements (Li, Ba, Sr, Ag, Hg, B) and macronutrients (Ca, Mg, K) in soil-orchid system on different bedrock types.

The mobility of chemical elements in the soil-orchid system has been poorly studied. The aim of this study is to evaluate the uptake and mobility of several trace (Li, Ba, Sr, Ag, Hg, and B) and macronutrients (Ca, Mg, and K) in the orchid Anacamptis morio (L.) R.M.Bateman, Pridgeon & M.W.Chase from soils in western Serbia. The sampling sites are characterized by three different bedrock types-cherts, limestones, and serpentines, which are the source of the significant chemical differences in the elemental status of the soil and plant tissues. The four-step Community Bureau of Reference sequential extraction procedure was used to determine the distribution of fractions and predict their potential phytoavailability. The orchid and soil samples were analyzed for total elemental content analysis using ICP-OES. The greatest potential for plant availability was determined for Ba and Sr, representing about 80% of the total soil content. More than 40% of Li in the soils was found to be potentially phytoavailable. Significant correlations were found between the total content of Li, B, and Sr in soils. Between 38 and 60% of Li content and more than 80% of Ba and Sr content were determined to be potentially phytoavailable by sequential analysis. The highest bioconcentration factor (> 1) was determined in the case of B and Sr for all orchid organs, while translocation factor for Li was highest in tubers and leaves. The studied elements were mainly stored in tubers and roots, indicating the exclusion strategy of A. morio as a metal tolerance mechanism. The data obtained showed significant differences in metal content in soils and plants originating from sites with different parent materials, suggesting that bedrock type and associated soil properties are important factors that determine chemical element mobility and uptake.

Effect of pH on metal mobility in the soil

pH is a parameter that can be used to estimate the mobility of chemical elements in the soil and can be used to measure the level of toxicity and soil pollution. The purpose of this study is to prove how far the influence of pH on metal mobility in the soil. Method that used in this study, 35 samples each 1 kg were taken from the soil profile in Cilengsi Bogor and then dried at room temperature. From each sample 20 grams were taken for pH and Eh measurements. The result of this study that the analysis showed a significant correlation between pH and Eh with r = 0.888. Although the samples are heterogeneous or come from different soils, there is still a positive correlation between metal concentration and pH (pH-Mn = 0.12; pH-Cd = 0.0058; pH-Pb = 0.39). This means that for homogeneous samples, the correlation between pH-metals will be more significant. Eh and soil pH variations depends on the activity and decomposition of carbon by plants and microorganisms. Therefore, it can be ideally be concluded that the topsoil Eh is higher than the bottom Eh. The aerobic-anaerobic boundary is at around 300 mV.

Metamorphic evolution of the Loma Marcelo skarn within the geotectonic context of the crystalline basement of the Ventania System (Argentina)

This study describes the mineralogical and isotopic changes that carbonate xenoliths experienced under multiple metamorphic events and hydrothermal fluid circulation during the evolution of the Ventania System basement. The high reactivity of carbonate xenoliths allowed the preservation of mineral assemblages corresponding to at least three metamorphic events in the resulting Loma Marcelo skarn. The Ventania System basement is composed of Neoproterozoic granites and ignimbrites, Early Cambrian granites, and Middle Cambrian rhyolites. Carbonate xenoliths were incorporated during the intrusion of a calc-alkaline granite with an LA-ICP-MS U-Pb crystallization age of 621.6 ± 2.2 Ma. The intrusion induced pyroxene–hornfels facies metamorphism in the carbonate xenoliths and the associated metasomatism generated calcic and magnesian skarns depending on the protolith composition. Garnet, clinopyroxene, wollastonite, bytownite, and meionite were formed in the calcic skarn (CaS), whereas forsterite and spinel were formed in the magnesian skarn (MgS). Crystallization of Early Cambrian alkaline granites was accompanied by intense hydrothermal activity that was responsible for low temperature (≤300 °C) F-metasomatism in the skarn, as evidenced by the presence of F-rich vesuvianite (CaS) and chondrodite (MgS), among other minerals. Vesuvianite was formed from calc-silicate mineral assemblages of the previous metamorphic event, whereas chondrodite was formed by replacement of forsterite. The low temperature formation of these typical high-grade minerals could be an evidence of mineral formation under disequilibrium conditions favoured by the high reactivity of hydrothermal fluids. Neopalaeozoic basement mylonitization under greenschist facies metamorphism was accompanied by hydrothermal fluid circulation. This event promoted extreme mobility of chemical elements in the basement rocks and epidotization (CaS) and serpentinization (MgS) in the Loma Marcelo skarn. The elongated and boudinaged shape of the skarn bodies, parallel to the mylonitic foliation, is a consequence of dextral shearing that affected the basement rocks. Additionally, almost pure grossular crystallized post-tectonically in the CaS. Carbonates of the Loma Marcelo skarn are depleted in 13C and 18O (δ13CV-PDB = −2.5/−10.1‰; δ18OV-SMOW = +7.3/+14.0‰) relative to carbonate sedimentary rocks. The δ13C and δ18O variations can be attributed to the interaction between large amounts of hydrothermal fluids (W/R = 30–50) and Neoproterozoic carbonate sedimentary rocks.

Chemical elements migration in water-travertin system (Tomsk region, Russia)

To assess the mobility of chemical elements in carbonate, formation processes have calculated the water migration coefficient -Kx and the geochemical mobility coefficient -Kn. The series of geochemical mobility were constructed. The elements that can be deposited and that can be accumulated in water have been distinguished. It is shown that anionic elements - Cl, S, Br, I, U, As, as well as elements such as Na, Mg, Mo, Zr well pass into solution from rocks and remain in the water. Elements such as Ca, Fe, Al, Mn, Si, Ba, Zn, Pb, Co, Hg, Ti, La, Ag, Sn, Cr are most fully deposited in travertines.

Mineralogy, petrography and geochemistry of an early Eocene weathering profile on basement granodiorite of Qaidam basin, northern Tibet: Tectonic and paleoclimatic implications

Weathering, as an important process in the earth surface system, can be significantly influenced by tectonics and climates over long time scales. Here, we use mineralogical, petrographic and geochemical data of a paleoweathering profile developed on basement granodioritic rocks of northern Qaidam basin, northern Tibet, to reconstruct early Eocene weathering conditions and to discuss how paleoclimates and tectonics dominated the weathering process. The results indicate that neoformed mineral phases in weathering products are dominated by smectite, and the profile has overwhelmingly low chemical index of alteration values (ca. 51–59) and significantly decreasing micropetrographic index values (from 25.0 to 0.2) from bottom to top. These findings suggest that the basement rocks experienced mild chemical weathering but relatively intensive physical weathering. We favor that non-steady-state weathering, in which mechanical erosion rates compare favorably with rates of chemical weathering, prevailed in northern Tibet during the early Eocene. The weathering conditions were likely an integrated response to active tectonism and dry climates at that time. Furthermore, chemical element mobility evaluation demonstrates that most of large ion lithophile elements and light rare earth elements (LREEs) of granodioritic rocks are quite active during weathering and can be easily leached even under mild chemical weathering conditions. Significant mass loss of Al and LREEs in upper weathered samples probably reflects acidic weathering conditions, which were likely due to extremely high atmospheric CO2 level during the early Eocene. This study, from the unique perspective of weathering process, suggests that intensive deformation and rapid tectonic erosion occurred in northern Tibet during the early Eocene, as a far-field response to the India-Eurasia collision. It also agrees with warm and relatively dry climates, which were likely attributed to the global greenhouse climates and the Paleogene planetary-wind-dominant climate system in Asia, respectively.

Influence of the plasma effect on the diffusion saturation of contacting surfaces in the chip formation zone

On the basis of totality of experimental data the offered model of mechanism of converting is into the zone of cutting superficially – active lubricating cooling technological facilities in radially active. The found out conformities to law of dependence of workability are permanent from totality actions of mechanical factors and thermal energy that appears as a result of recombination of the ionized hydrogen in area of alteration and break of forces of connections. It is shown that efficiency that appeared radially lasant bound by co-operating of the positively charged electric parts of hydrogen with the new electric active real structure that arises up as a result of the mechanical operating on a metal. The analysis of researches shows in the contiguous areas of science, that the speed (impulsive) heating of steel is the effective method of influence on structural to the state of metal. For example, at the speed heating of steel an austenite is formed in the extraordinarily short intervals of time, without regard to his diffusive nature of formation. It was envisaged in this connection, in the zone formation of form of shaving that appears as a result of co-operating of protons with the real structure of contacting surfaces of purveyance with an instrument, impulsive thermal energy can cause the structural changes of metals and diffusive mobility of chemical elements of pyropolymeric remain similarly, in particular to the carbon. The veritable specific of heating at a thermal flash, presumably, consists in that thermal energy is needed for the different phase and structural changes of сталей created directly in a reactive volume, but not acts to it from peripheral areas due to a heat-conducting, as it takes place at the external heating. In connection with the stated researches of influence of specific terms that is created in the zone of contact of wedge of instrument with a purveyance were conducted, that created in connection with the chemical activating of lubricating cooling technological facilities. The got results allow to draw conclusion however, that a frequent increase of wearproofness of instrument at mechanically plasma treatment, is the consequence of a few factors : decline of forces of cutting, reduction to the coefficient of friction of surfaces of instrument with the processed material and filling of instrument of loss of carbon cutting edges. It means that the use of polymers as additives to lubricating cooling technological facilities, that provide display of plasma effect in the zone of destruction it is possible to examine also, as one of directions of possibility of creation of hydrogen technology of chemically heat treatment of construction to steel with the aim of acquisition of optimal physics – mechanical properties.

Magmatismo basáltico do Andar Alagoas (Bacia de Campos)

Magmatismo associado com o estágio pré-evaporítico da Bacia de Campos foi estudado a partir de testemunhos de quatro furos de sondagens. Os dados levantados são importantes no contexto da evolução tectônica e estratigráfica da bacia. O objetivo deste trabalho foi a caracterização dessas rochas a partir da petrografia, litoquímica, química mineral e composição isotópica Sr-Nd. A aplicação das metodologias de estudo convencionais foi dificultada devido ao grau de alteração das rochas, marcado por modificações mineralógicas (substituição de minerais por argilominerais, palagonitização do vidro vulcânico, sericitização dos plagioclásios e presença de vesículas), ao elevado valor de perda ao fogo (LOI) e à identificação de sedimentos arenosos englobados pela rocha vulcânica. Para minimizar os efeitos da alteração, empregaram-se metodologias que permitiram avaliar o grau de alteração das amostras e a mobilidade dos elementos químicos na rocha total. Os resultados obtidos estabelecem que as rochas vulcânicas são basaltos originados a partir de magmas com composição subalcalina, toleítica a transicional, baixo TiO2 e alto magnésio. Os elementos terras raras (ETR) e o padrão de distribuição dos elementos traço estão em conformidade com o padrão dos basaltos toleíticos baixo TiO2 da Formação Serra Geral e são diferentes dos enriched-mid ocean ridge basalt (E-MORB) e dos ocean island basalts (OIB) do oceano Atlântico, embora alguns elementos tenham comportamento similar. O piroxênio dominante é a augita e, quimicamente, confirma que os basaltos pertencem à série subalcalina, bem como ao intervalo de transição entre as séries cálcio-alcalina e toleítica. Isotopicamente, as amostras estudadas incidem fora do campo estabelecido como “mantle array”; e seguem o comportamento dos basaltos da Bacia de Campos com alto potássio. Os parâmetros levantados estabelecem a correlação das rochas vulcânicas do Andar Alagoas da Bacia de Campos com os basaltos intracontinentais da Bacia do Paraná.

Quantifying magma mixing with the Shannon entropy: Application to simulations and experiments

We introduce a new quantity to petrology, the Shannon entropy, as a tool for quantifying mixing as well as the rate of production of hybrid compositions in the mixing system. The Shannon entropy approach is applied to time series numerical simulations and high-temperature experiments performed with natural melts. We note that in both cases the Shannon entropy increases linearly during the initial stages of mixing and then saturates toward constant values. Furthermore, chemical elements with different mobilities display different rates of increase of the Shannon entropy. This indicates that the hybrid composition for the different elements is attained at different times generating a wide range of spatio-compositional domains which further increase the apparent complexity of the mixing process.Results from the application of the Shannon entropy analysis are compared with the concept of Relaxation of Concentration Variance (RCV), a measure recently introduced in petrology to quantify chemical exchanges during magma mixing. We derive a linear expression relating the change of concentration variance during mixing and the Shannon entropy.We show that the combined use of Shannon entropy and RCV provides the most complete information about the space and time complexity of magma mixing. As a consequence, detailed information about this fundamental petrogenetic and volcanic process can be gathered. In particular, the Shannon entropy can be used as complement to the RCV method to quantify the mobility of chemical elements in magma mixing systems, to obtain information about the rate of production of compositional heterogeneities, and to derive empirical relationships linking the rate of chemical exchanges between interacting magmas and mixing time.

Time evolution of chemical exchanges during mixing of rhyolitic and basaltic melts

We present the first set of chaotic mixing experiments performed using natural basaltic and rhyolitic melts. The mixing process is triggered by a recently developed apparatus that generates chaotic streamlines in the melts, mimicking the development of magma mixing in nature. The study of the interplay of physical dynamics and chemical exchanges between melts is carried out performing time series mixing experiments under controlled chaotic dynamic conditions. The variation of major and trace elements is studied in detail by electron microprobe and Laser Ablation ICP-MS. The mobility of each element during mixing is estimated by calculating the decrease in the concentration variance in time. Both major and trace element variances decay exponentially, with the value of exponent of the exponential function quantifying the element mobility. Our results confirm and quantify how different chemical elements homogenize in the melt at differing rates. The differential mobility of elements in the mixing system is considered to be responsible for the highly variable degree of correlation (linear, nonlinear, or scattered) of chemical elements in many published inter-elemental plots. Elements with similar mobility tend to be linearly correlated, whereas, as the difference in mobility increases, the plots become progressively more nonlinear and/or scattered. The results from this study indicate that the decay of concentration variance is in fact a robust tool for obtaining new insights into chemical exchanges during mixing of silicate melts. Concentration variance is (in a single measure) an expression of the influence of all possible factors (e.g., viscosity, composition, and fluid dynamic regime) controlling the mobility of chemical elements and thus can be an additional petrologic tool to address the great complexity characterizing magma mixing processes.

Horizontal zonation of the territory of the Ukrainian Shield for mobility of chemical elements in soil sediments

Horizontal zonation of the territory of the Ukrainian Shield for mobility of chemical elements in soil sediments

Geochemical Mobility of Chemical Elements in Saline Lake Systems in Khakassia (Russia)

Saline lakes were sampled from the semi-arid region of the Russian Federation (Khakassia). The water and salt sediment samples were collected from 4 lakes: Khamiskol, Terpikol, Uskol, and Tus. The total dissolved solids (TDS) of the various lakes ranges from 7.9 to 115.6g/l. The pH values lie mostly in the range of 8.3 – 9.9. The anionic composition of saline lakes is varied. The cationic composition of lakes is not so varied as the anionic one. Sodium is the dominant cation in the water composition of these lakes, whereas the Tus Lake contains magnesium and sodium in equal proportions. The chemical element enrichment of water is regulated by the formation of significant quantities of secondary mineral phases. The Khakassia saline lakes are saturated with respect to carbonate minerals such as calcite, dolomite, magnesite, and are undersaturated in terms of natrite, anhydrite, thenardite, and halite. Geochemical mobility coefficients can be used to evaluate the geochemical mobility of major elements in the saline lake waters. Geochemical mobility coefficients suggest that trace elements tend to accumulate in secondary phases, which are consolidated by secondary mineral precipitation and sorption processes.

Morphochemistry of patterns produced by mixing of rhyolitic and basaltic melts

In this work we present the results of time series experiments performed by mixing basaltic and rhyolitic melts at high temperature using a device recently developed to trigger chaotic dynamics in a mixing system. The morphology of mixing patterns is quantified at different times by measuring their fractal dimension and a linear relationship is derived between mixing time and morphological complexity. The complexity of mixing patterns is also compared to the degree of homogenization of chemical elements during mixing and empirical relationships are established between the fractal dimension and the temporal variation of concentration variance of elements.New concepts and tools to study the magma mixing process unfold from the experimental results presented in this work. The first one is that the mixing patterns are fractals and they can be quantified by measuring their fractal dimension. This represents a further step in the quantification of the magma mixing process. The second outcome is that the relationship between the fractal dimension of the mixing patterns and mixing time is linear. This has important volcanological implications as the analyses of the morphology of mixing patterns in volcanic rocks can be complemented by experiments to build a new chronometer to estimate the mixing-to-eruption time. A further result from this work is the relationship between the fractal dimension of mixing patterns and concentration variance of chemical elements. This represents the first morphochemical study in igneous petrology bringing with it the potential to infer the relative mobility of chemical elements during the time progression of mixing by analyzing the morphology of mixing patterns in the rocks.

Relaxation of concentration variance: A new tool to measure chemical element mobility during mixing of magmas

The ability of chemical elements to diffuse in silicate melts is central to igneous processes. It controls the rates of phase transitions such as crystal growth and dissolution kinetics, the rate of homogenization of compositional gradients generated by fractional crystallization and assimilation of country rocks as well as one of the most intriguing processes of all, magma mixing.A very useful measure, commonly used to quantify the rate of homogenization of chemical elements in silicate melts, is the diffusion coefficient. It is widely approximated to be of a constant value (at a fixed pressure and temperature) for a melt with a given composition and rheology. When dealing with magma mixing processes, melts with different initial compositions and rheological properties (e.g. basalt and rhyolite) coexist in the same system. Under such circumstances, the compositional and rheological dependence of diffusion coefficients must be considered, leading to a considerable increase of complexity in the modeling of magma mixing. Yet, an additional and even more dramatic increase in complexity is due to the fact that the mixing of magmas is undoubtedly a very dynamic process. Scale-invariant distributions of filaments of different melts are generated by stretching and folding dynamics. This has a dual effect on the mobility of chemical elements. On the one hand their mobility increases because of an exponential increase of contact area. On the other hand, mobility can be buffered by the different diffusivities in the melts (larger in the low-viscosity than in the high-viscosity melt). Uphill diffusion of chemical elements is likely to develop at the interface between interacting magmas, further increasing the complexity of the process.Here we aim to understand chemical element mobility during melt homogenization in a magma mixing event under dynamic conditions. We have performed experiments by mixing phonolitic and alkali-basaltic melts. The mixing process was induced using a high-temperature centrifuge apparatus. The rotating speed and acceleration during all experiments were 1850rpm and 1000g, respectively. Experiments were performed for 5, 20 and 120min. Samples were arranged in a buoyantly unstable geometry, with the denser material placed at the inner side of the rotating circle, resulting in injection of the mafic melt into the felsic melt during rotation. The temperature during experimental runs was 1200 (±1)°C.From the resultant glasses, vortex-like structures generated by repeated stretching and folding dynamics were observed at the interface between the two melts. The concentrations of major and trace elements were then measured along interfaces by electron microprobe and LA-ICP-MS. The mobility of each element was next quantified by calculating the decrease (or relaxation) of concentration variance with time. The first notable result is that for major and trace elements, concentrations variance decays exponentially. The exponent of the exponential function is then chosen as a measure of element mobility. Our results show clearly that different chemical elements homogenize in the melt at differing rates. Amongst the major elements Na is the fastest element followed by Al, Mg, Ca, K and Si. The trace elements, Ba, Rb, Sr, Nb and Zr exhibit similar mobilities. The REE display the lowest mobility and they show a systematic decrease from light to heavy.The results from this study indicate that the decay of concentration variance is a robust tool for obtaining new insights into chemical exchanges during the mixing of silicate melts. Concentration variance includes in a single measure an expression of the influence of all possible factors (e.g. viscosity, composition, fluid-dynamic regime) controlling the mobility of chemical elements during the mixing of two liquids. A new parameter, the Relaxation of Concentration Variance (RCV), is proposed as an effective tool for quantifying the homogenization of chemical elements during the mixing of silicate melts.

The space and time complexity of chaotic mixing of silicate melts: Implications for igneous petrology

We present new experimental results on the study of the space and time modulation of compositional fields during chaotic mixing between mafic and felsic silicate melts. The experimental strategy was planned using numerical simulations performed using the experimental geometry. These mixing experiments were performed using a recently developed experimental apparatus, which is capable of mixing high-viscosity silicate melts at high temperatures and under precisely controlled conditions of fluid-dynamics and strain. The compositional variability produced by the mixing process was investigated both along linear analytical transects and on high-resolution 2D X-ray maps, covering the mixing patterns.Our results indicate that chaotic flow fields represent very powerful dynamics to blend silicate melts, even under laminar fluid dynamic conditions (Reynolds number ca. 10−7) and for dissimilar melts with high viscosity ratios (on the order of 103). The repetition of stretching and folding processes between the two melts induced a strong increase of contact interfaces thus favoring efficient chemical exchanges. As a result the initial mafic composition is no longer detectable in the mixing system after ca. 2h (i.e. the duration of the experiment). A further important result is the observation of highly non-linear patterns in inter-elemental plots produced by the onset of diffusive fractionation processes. This is contrary to common thinking that magma mixing should always produce linear trends between pairs of chemical elements.A new measure, the “concentration variance”, is proposed to quantify chemical element mobility during the mixing process. This measure is statistically robust and can be quantitatively used to measure chemical element mobility independently of the geometry in which the compositional variation (i.e. transects, areas, etc.) is embedded or the local strain history of the mingling.Our results highlight concentration variance as a robust probe of the as yet poorly-understood processes involved in the common petrological process of magma mixing.

Micro- and nano-textural evidence of Ti(–Ca–Fe) mobility during fluid–rock interactions in carbonaceous lawsonite-bearing rocks from New Zealand

Understanding the mobility of chemical elements during fluid–rock interactions is critical to assess the geochemical evolution of a rock undergoing burial and metamorphism and, more generally, to constrain the geochemical budget of the subduction factory. In particular, determining the behavior and mobility of Ti in aqueous fluids constitutes a great challenge that is still under scrutiny. Here, we study plant fossils preserved in blueschist metasedimentary rocks from the Marybank Formation (New Zealand). Using scanning and transmission electron microscopies (SEM and TEM), we show that the carbonaceous material (CM) composing the fossils contains abundant nano-inclusions of Ti- and Fe-oxides. These nanocrystals are mainly anatase, rutile, and Fe–Ti oxides. The mineral composition observed within the fossils is significantly different from that detected in the surrounding rock matrix. We propose that Ti and Fe might have been mobilized by the alteration of a detrital Ti–Fe-rich protolith during an early diagenetic event under acidic and reducing conditions. Aqueous fluids rich in organic ligands released by the degradation of organic matter may have been involved. Moreover, using mass balance and petrological observations, we show that the contrasted mineralogy between the rock matrix and the fossil CM might be the consequence of the chemical isolation of fossil CM during the prograde path of the rock. Such an isolation results from the early formation of quartz and Fe-rich phyllosilicate layers enclosing the fossil as characterized by SEM and TEM investigations. Overall, this study shows that investigating minerals associated with CM down to the nanometer scale in metamorphic rocks can provide a precious record of early prograde geochemical conditions.