Concentration Of Light Elements Research Articles

Effect of discretization choices when modeling the thermo-chemical history of the accreting core

Different discretizations methods applied to models of core/mantle segregations are tested (single stage, multistage accretion, results of N-body simulations) in order to test the sensitivity of the thermo-chemical coupling to the type of discretization used. We found that while single stage and large discretization of segregation steps yield very different core temperature, multistage models of accretion and core mantle segregation, at least for the model presented in this paper, tend to yield similar results, whether it is for the light element concentrations or the final temperature of the core. As long as a magma ocean existence throughout the entire process of core/mantle segregation is posited, and that only the impactor's masses of metal and silicate are re-equilibrated at each step, the degree of discretization of continuous model does not matter as long as it encompasses more than 10 steps of calculations.

Submicronic-Scale Mechanochemical Characterization of Oxygen-Enriched Materials.

Conventional techniques that measure the concentration of light elements in metallic materials lack high-resolution performance due to their intrinsic limitation of sensitivity. In that context, scanning microwave microscopy has the potential to significantly enhance the quantification of element distribution due to its ability to perform a tomographic investigation of the sample. Scanning microwave microscopy associates the local electromagnetic measurement and the nanoscale resolution of an atomic force microscope. This technique allows the simultaneous characterization of oxygen concentration as well as local mechanical properties by microwave phase shift and amplitude signal, respectively. The technique was calibrated by comparison with nuclear reaction analysis and nanoindentation measurement. We demonstrated the reliability of the scanning microwave technique by studying thin oxygen-enriched layers on a Ti-6Al-4V alloy. This innovative approach opens novel possibilities for the indirect quantification of light chemical element diffusion in metallic materials. This technique is applicable to the control and optimization of industrial processes.

A STUDY OF IMPROVEMENT OF A TECHNOLOGY FOR OBTAINING RADIATION-PROTECTING MATERIALS FOR SPACECRAFT AND ROCKETRY SYSTEMS


 
 
 Abstract. The use of commercial integrated circuits (ICs) in the electronic equipment of the spacecraft entails a certain risk. This is due to the fact that some commercial ICs are not suitable for operating conditions in space, most have a functional failure rate of about 10 krad per total accumulated dose (ie quite low), durability is not controlled from lot to lot, and reliability in extreme operating conditions is not defined. The object of development and research were the processes of interaction of materials with corpuscular radiation in a wide range of energies, and the subject of research was the shielding of electron and proton flows with energies up to 100 MeV by disperse -filled composite materials with a polymer matrix. A promising way to increase the survivability of the spacecraft by reducing the accumulated radiation dose is the use of protective materials that effectively protect the BEA from the radiation flow. The analysis of the current state of protection of radio- electronic equipment of space technology made it possible to establish that the most effective protection can be achieved by optimally combining the content of light and heavy elements in the composite material (CM). Modern research is aimed at obtaining composite materials that have the ability to weaken and disperse both light and heavy elementary particles. In the State University named after O. Honchar developed fundamentally new composite materials, which are superior in protection efficiency to those used today - metal ones, and are not inferior to the best world analogues. Preliminary results of theoretical and experimental research, including the use of computer modeling and simulation experiments on electron and proton accelerators, made it possible to draw conclusions about the possibility of increasing the complex of protective properties and prospects of the materials being created. The flow of high-energy electrons decreases by 1.4 times, and protons by 1.6 times compared to aluminum alloys. Enterprises of the space industry of Ukraine have shown great interest in the use of new protective materials. Analysis of the available information shows that the created materials are superior in operational parameters to those used today in China, Russia, Ukraine and other space countries. According to theoretical calculations, CM samples were developed, which have a higher stopping power of electrons than aluminum or its alloys, which are currently used in space vehicles in almost the entire range of the spectrum characteristic of GSO. Studies using the ELIAS linear electron accelerator showed that the obtained KM samples are more than 1.3 times more effective in terms of protective properties compared to aluminum at electron energies of the order of 2-3 MeV . There are prerequisites for obtaining an even more effective attenuation of the electron flow in comparison with the "reference" aluminum due to the variation of both the qualitative composition of the CM and its structure.
 
 

Density deficit of Earth's core revealed by a multimegabar primary pressure scale.

An accurate pressure scale is a fundamental requirement to understand planetary interiors. Here, we establish a primary pressure scale extending to the multimegabar pressures of Earth's core, by combined measurement of the acoustic velocities and the density from a rhenium sample in a diamond anvil cell using inelastic x-ray scattering and x-ray diffraction. Our scale agrees well with previous primary scales and shock Hugoniots in each experimental pressure range and reveals that previous scales have overestimated laboratory pressures by at least 20% at 230 gigapascals. It suggests that the light element content in Earth's inner core (the density deficit relative to iron) is likely to be double what was previously estimated, or Earth's inner core temperature is much higher than expected, or some combination thereof.

The Geochemical Legacy of Low-Temperature, Percolation-Driven Core Formation in Planetesimals

Mechanisms for core formation in differentiated bodies in the early solar system are poorly constrained. At temperatures below those required to extensively melt planetesimals, core formation could have proceeded via percolation of metallic liquids. Although there is some geochemical data to support such ‘low-temperature’ segregation, experimental studies and simulations suggest that percolation-driven segregation might have only contributed to core formation in a proportion of fully-differentiated bodies. Here, the effects low-temperature core-formation on elemental compositions of planetesimal cores and mantles are explored. Immiscibility of Fe-rich and FeS-rich liquids will occur in all core-formation models, including those involving large fraction silicate melting. Light element content of cores (Si, O, C, P, S) depends on conditions under which Fe-rich and FeS-rich liquids segregated, especially pressure and oxygen fugacity. The S contents of FeS-rich liquids significantly exceed eutectic compositions in Fe–Ni–S systems and cannot be reconciled with S-contents of parent bodies to magmatic iron meteorites. Furthermore, there is limited data on trace element partitioning between FeS-rich and Fe-rich phases, and solid/melt partitioning models cannot be readily applied to FeS-rich liquids. Interaction of metallic liquids with minor phases stable up to low fraction silicate melting could provide a means for determining the extent of silicate melting prior to initiation of core-formation. However, element partitioning in most core-formation models remains poorly constrained, and it is likely that conditions under which segregation of metallic liquid occurred, especially oxygen fugacity and pressure, had as significant a control on planetesimal composition as segregation mechanisms and extent of silicate melting.

Determination of carbon, oxygen, hydrogen and nitrogen content in coals using WDXRF scattering spectra

A new approach to determination of light elements (C, O, H and N) content in coals by using Х-Ray fluorescence (XRF) method in combination with partial least squares (PLS) regression was studied. The quantitative content of light elements was determined by studying the spectra of coherent and incoherent scattering of the primary radiation of the X-Ray tube for compressed samples of coals of various brands. The study shows that hidden differences in the scattering spectra can be used for quantification of elements that are typically impossible to quantify using XRF. The information obtained can be used to improve semi-quantitative methods of XRF based on fundamental parameters (FP).

Quantitative analysis of Li, Na and K in single-element standard solutions using portable laser-induced breakdown spectroscopy

Laboratory-based laser-induced breakdown spectroscopy (LIBS) instruments have proven themselves for trace element analysis of an extensive range of elements. As portable devices have evolved greatly in recent years, new areas of field application are opening up. However, no portable LIBS (pLIBS) has yet been used for quantitative inorganic water analysis. The aim of this study was to explore whether pLIBS combined with a surface-enhanced liquid-to-solid conversion method can quantify light alkali element concentrations in standard solutions. Multivariate calibrations were performed with single-element standard solutions at detection limits of 0.006, 0.011 and 0.007 mg l −1 for Li, Na and K, respectively. Coefficients of determination ( R 2 ) for the calibration lines from 0.1 to 100 mg l −1 for Li and Na, and 0.1 to160 mg l −1 for K were between 0.96 and 0.99. It has been shown that the surface preparation technique used improves the homogeneity of the spread and shape of the evaporation residue and thus the accuracy and precision of the analysis. Hence, this study demonstrates that it is possible to quantify light alkali metals in single-element standard solutions in the range of 0.1 to 160 mg l −1 using handheld LIBS.

Development of Nondestructive Elemental Analysis System for Hayabusa2 Samples Using Muonic X-rays

The concentrations of carbon and other major elements in asteroid samples provide very important information on the birth of life on the Earth and the solar-system evolution. Elemental analysis using muonic X-rays is one of the best analytical methods to determine the elemental composition of solid materials and, notably, is the only method to determine the concentration of light elements in bulk samples in a nondestructive manner. We developed a new analysis system using muonic X-rays to measure the concentrations of carbon and other major elements in precious and expectedly tiny samples recovered from the asteroid Ryugu by spacecraft Hayabusa2. Here we report the development process of the system in 4 stages and their system configurations, The analysis system is composed of a stainless-steel analysis chamber, an acrylic glovebox for manipulating asteroid samples in a clean environment, and Ge semiconductor detectors arranged to surround the analysis chamber. The performance of the analysis system, including the background level, which is crucial for the measurement, was greatly improved from the first stage to the later ones. Our feasibility study showed that the latest model of our muonic X-ray analysis system is capable of determining the carbon concentration in Hayabusa2’s sample model with an uncertainty of less than 10% in a 6 day measurement.

Rare Earth Elements behaviour in different types of mineral waters within Baikal Lake

The current study contains a review of the REE abundance and distribution in thermal and cold mineral waters which are widely spread around Baikal Lake. Studied mineral waters were divided into CH4, N2 and CO2-rich waters by the associated gas composition. We found that the highest REE concentrations were connected with thermal waters that were accumulated in swamps (slow-moving waters). Another core process for accumulating of REE in waters is the rock weathering in CO2 presence. This study shows that there are no correlations between REE and main ions, Eh, TDS and temperature. But dependence of REE on pH and positive correlations of REE with Al, P, Mn, V, Cu, Pb and As, which indicate common processes of microelements migration, were established. Within the study waters the light REE concentrations dominate over heavy REE. The presence of CO2 gas increases heavy REE concentrations, and concentrations of several light elements (La, Ce, Nd). The observed differences in REE contents in studied waters can be provenance dependent and possibly relate to more complicated evolutionary processes as water circulation time, depth and mixing. This is the first investigation of REE distribution and abundance in mineral waters of the Baikal Lake.

The iron spin transition of deep nitrogen-bearing mineral Fe3N1.2 at high pressure

Abstract Nitrogen is an essential element for life, one of the most abundant volatiles in the atmosphere, and an important component in the Earth’s interior, where iron nitride is an essential host of deep nitrogen. Here, we investigate the pressure-induced electronic spin-pairing transition of iron in siderazot (Fe3N1.2) at pressures up to 45.8 GPa at room temperature, using diamond-anvil cell techniques coupled with synchrotron X-ray emission spectroscopy. The integrated intensity of the satellite emission peak (K′β) decreases upon compression but remains unchanged at pressures greater than 30.5 GPa. In other words, the high-spin to low-spin transition of iron in Fe3N1.2 starts immediately at very low pressures and completes at ~30.5 GPa. The iron spin transition completion pressures increase with the nitrogen concentration of hexagonal close-packed iron nitrides (i.e., Fe3N1.2, Fe7N3, and Fe2N). Moreover, the identity and concentration of light elements in binary iron-rich compounds such as Fe3N, Fe3C, Fe3P, Fe3S, Fe7C3, and Fe7N3, together with their crystal structure, could affect the iron spin transition pressures. The spin transition of iron-rich alloys could alter the bonding nature and the physical properties, including the thermal and electrical conductivity, thereby influencing the thermal state and evolution of planetary interiors.

Application of the medical linear accelerator ELEKTA AXESSE in the study of sorption properties of impurities and absorption coefficients of medium and heavy chemical elements

In this article, the authors propose a new technique for measuring linear attenuation coefficients on the medical linear accelerator Elekta Axesse. Linear attenuation coefficients were obtained for four samples at different concentrations of substances at a gamma-ray energy of 6 MeV. A unified ionization chamber was used as a detector to register the transmitted gamma-ray beam through the samples under study. Linear absorption coefficients were obtained for elements B, C, O, S, Fe, Ba taking into account their concentration, as well as taking into account the different mass inclusion of paraffin in the samples under study, which is acyclic hydrocarbons CnH2n+2. The measurement results showed that taking into account certain components in impurities leads to relatively small, but quite noticeable differences in the determination of the total absorption coefficients. This is especially important to take into account for determining the concentration of light elements in samples. To determine the content of medium and heavy chemical elements, taking into account the content of light elements can be neglected. The use of a 6 MeV gamma-ray beam made it possible to reduce the errors in determining the absorption coefficients, since their dependence on energy in the region of applicable gamma-ray energies is not so great in comparison with the low-energy region, in which the shell effects for heavy elements will introduce significant contribution.

Hydrothermal Fluids-Rock Interactions in the Geothermal Area of the Ngebel Volcano Complex Ponorogo, East Java, Indonesia

The Ngebel geothermal area is morphologically in several volcanic cones arranged as lava domes, volcanic hills, and lake craters. Volcanic cones are composed of lava, pyroclastic falls, pyroclastic flows, volcanic cones such as Jeding Volcano, Kemlandingan Volcano, Manyutan Volcano, and Ngebel Volcano. The magmatism activity that occurs in this area is andesitic-dacitic and also forms a geothermal system. This geothermal system is estimated to produce 50 MWe. During the formation of a geothermal system, hydrothermal fluids interact with the surrounding rock. Based on the results of geological mapping, petrographic analysis, and analysis of rare earth elements. In general, the results of rock-fluid interactions show a decrease in the concentration of rare earth elements, both light and heavy REE elements, from andesite basaltic samples to cold water samples. However, an unexpected reduction from 10 times chondrite to 0.3 times chondrite from hot water to cold water. This research will contribute to the hydrothermal alteration process in the research area that previous researchers have never done and expect to provide new information about forming the geothermal system in the Ngebel Volcanic Complex area.

Physical Properties and Internal Structure of the Central Region of the Moon

One of the pivoting problems of the geochemistry and geophysics of the Moon is the structure of its central region, i.e., its core and adjacent transition layer located at the boundary between the solid mantle and liquid or partially molten core. The chemical composition of the mantle and the internal structure of the central region of the Moon were simulated based on the joint inversion of seismic, selenophysical, and geochemical parameters that are not directly interrelated. The solution of the inverse problem is based on the Bayesian approach and the use of the Markov chain Monte Carlo algorithm in combination with the method of Gibbs free energy minimization. The results show that the radius of the Moon’s central region is about 500–550 km. The thickness of the transition layer and the radii of the outer and inner cores relatively weakly depend on the composition models of the bulk silicate Moon with different contents of refractory oxides. The silicate portion of the Moon is enriched in FeO (12–13 wt %, FeO ~ 1.5 × BSE) and depleted in MgO (Mg# 79–81) relative to the bulk composition of the silicate Earth (BSE), which is in conflict with the possibility of the formation of the Moon from the Earth’s primitive mantle and does not find an adequate explanation in the current canonical and non-canonical models of the origin of the Moon. SiO2 concentrations in all zones of the lunar mantle vary insignificantly and amount to 52–53 wt %, and the predominant mineral of the upper mantle is low-Ca orthopyroxene but not olivine. With respect to Al2O3, the lunar mantle is stratified, with a Al2O3 content higher in the lower mantle than in all overlying shells. The partially molten transition layer surrounding the core is about 200–250 km thick. The radii of the solid inner core are within 50–250 km, and the most probable radii of the liquid outer core are ~300–350 km. The physical characteristics of the lunar core are compared with experimental measurements of the density and speed of sound of liquid Fe(Ni)–S–C–Si alloys. If the seismic model of the liquid outer core with VP = 4100 ± 200 m/s (Weber et al., 2011) is reasonably reliable, then this uncertainty range is in the best agreement with the VP values of 3900–4100 m/s of liquid Fe(Ni)–S alloys, with sulfur content up to ~10 wt % and a density of 6200–7000 kg/m3, as well as with the inverted values of density and velocity of the outer core. The VP values of liquid Fe–Ni–C and Fe–N–Si alloys at 5 GPa exceed seismic estimates of the speed of sound of the outer lunar core, which indicates that carbon and silicon can hardly be dominant light elements of the lunar core. The inner Fe(Ni) core (possibly with an insignificant content of light elements: sulfur and carbon) is presumably solid and has a density of 7500–7700 kg/m3. The difference in density between the inner and outer cores Δρ ~ 500–1000 kg/m3 can be explained by the difference in their composition.

A seismometer maps Mars’s anatomy

NASA’s InSight is the first mission to explore seismic waves in a planetary body since Apollo 17 in 1972.

Beryllium determination in non-optimal matrices using the $^{9}$\textbf{Be(d,n$\gamma )$}$^{10}$\textbf{B}

An alternative method for the detection of beryllium in light element matrices is proposed, implementing the use of a deuteron beam at energies from 1 to 2.1 MeV and the $^{9}$Be(d,n$\gamma )^{10}$B reaction. A HP GE detector of 20{\%} relative efficiency was used to detect the 718 keV gamma ray of $^{10}$B. The minimum detection limits obtained for beryllium, are compared to those taken with other NRA techniques (PIGE, heavy-ion and charged-particle spectroscopy) in complex matrices containing high concentrations of light elements. The absolute $\gamma $-ray yield of the reaction is also compared to absolute $\gamma $-ray yields from literature.

How many explosions does one need? Quantifying supernovae in globular clusters from iron abundance spreads

ABSTRACT Many globular clusters (GCs) are known to host multiple populations distinguishable by their light-element content. Less common are GCs displaying iron abundance spreads that are seen as evidence for enrichment through core collapse supernovae (SNe). We present a simple analytical method to estimate the number of SNe required to have occurred in a GC from its metallicity and iron abundance spread. We then use this result to estimate how long star formation (SF) lasted to build the GC. We apply our method to up-to-date measurements and find that, assuming the correctness of these measurements, multiple SNe (up to 105) are required in most GCs with iron abundance spreads. The number of SNe events that contributed to the enrichment of the GCs studied here is typically a factor of 10 less than the expected number of SNe in a canonical initial mass function (IMF). This indicates that gas expulsion from the forming GC occurred after the first 10 per cent of SNe exploded. We compute that for the GCs typically SF ends after only a few Myr (extending up to ${\approx}30 \, \rm Myr$ in a few cases). We also discuss possible improvements of this method and especially its sensitivity to the error of iron abundance measurements of individual stars of a GC. The method presented here can quickly give an estimate for the number of SNe required to explain the iron abundance spread in a GC without the requirement of any hydrodynamical simulations.

Petrochemical features of tholeiites from the Shaka ridge (South Atlantic)

The article presents original data of chemical composition of tholeiitic basaltoids and andesites, dredged from the Shaka Ridge (South Atlantic) in the course of field research in spring 2016 on the scientific expedition vessel “Akademik Fedorov”. The analytical part of the work on estimating the contents of petrogenic, trace and rare-earth elements was carried out using the classical method (“wet chemistry”), X-ray fluorescence analysis (XRF) and inductively coupled plasma mass spectrometry (ICP-MS). The studied samples demonstrate elevated concentrations of large-ion lithophile elements, or LILE, (Ba, Rb, Pb) and light rare earth elements, or LREE, (La, Ce, Nd, Sm) relative to high field strength elements, or HFSE, (Nb, Ta) and heavy rare earth elements, or HREE, (Dy, Yb, Lu). The specifics of trace element geochemistry suggest a significant contribution of crustal or subduction components to the magmas of the Shaka Ridge. Discrimination diagrams of basaltoids and allied rocks with fields of different geodynamic settings indicate that they were formed in the setting of the mid-ocean ridge basalt (MORB). The reason behind the appearance of subduction and crustal marks in the rocks is possibly associated with assimilation of crustal matter by magmas or lies in their inheritance from the mantle source.

Linking globular cluster structural parameters and their evolution: multiple stellar populations

ABSTRACT Globular clusters (GCs) are known to host multiple stellar populations showing chemical anomalies in the content of light elements. The origin of such anomalies observed in Galactic GCs is still debated. Here we analyse data compiled from the Hubble Space Telescope, ground-based surveys, and Gaia Data Release 2 (DR2) and explore relationships between the structural properties of GCs and the fraction of second population (2P) stars. Given the correlations we find, we conclude that the main factor driving the formation/evolution of 2P stars is the cluster mass. The existing strong correlations between the 2P fraction and the rotational velocity and concentration parameter could derive from their correlation with the cluster mass. Furthermore, we observe that increasing cluster escape velocity corresponds to higher 2P fractions. Each of the correlations found is bimodal, with a different behaviour detected for low- and high-mass (or escape velocity) clusters. These correlations could be consistent with an initial formation of more centrally concentrated 2P stars in deeper cluster potentials, followed by a long-term tidal stripping of stars from clusters outskirts. The latter are dominated by the more extended distributed first population (1P) stars, and therefore stronger tidal stripping would preferentially deplete the 1P population, raising the cluster 2P fraction. This also suggests a tighter distribution of initial 2P fractions than observed today. In addition, higher escape velocities allow better retention of low-velocity material ejected from 1P stars, providing an alternative/additional origin for the observed differences and the distributions of 2P fractions amongst GCs.

Zircon Chemistry and Oxidation State of Magmas for the Duobaoshan-Tongshan Ore-Bearing Intrusions in the Northeastern Central Asian Orogenic Belt, NE China

The Duobaoshan (DBS)-Tongshan (TS) porphyry Cu–(Mo) deposit (4.4 Mt Cu, 0.15 Mt Mo) is located in the northeastern part of the central Asian orogenic belt (CAOB) in northeastern China. It is hosted by early Ordovician dioritic to granodioritic intrusions which are characterized by the subduction-related geochemical signatures including high concentrations of large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and low concentrations of heavy REEs (HREEs) and high-field -strength elements (HFSEs), such as Nb, Ta, Zr and Ti in bulk rock compositions. Furthermore, they show adakitic geochemical signatures of high Sr/Y ratios (29~55) due to high Sr (290~750 ppm) and low Y (<18 ppm). Zircon trace element abundances and published Sr-Nd-Hf isotope data of these rocks suggest that the parental magmas for these ore-bearing intrusions were rich in H2O and formed by partial melting of a juvenile lower crust/lithospheric mantle or metasomatized mantle wedge during the northwestward subduction of the Paleo-Asian Ocean before the collision of the Songnen block with the Erguna-Xing’an amalgamated block in the early Carboniferous. Values of Ce4+/Ce3+ and Ce/Nd in zircons are 307~461 and 14.1~20.3 for mineralized granodiorites, and 231~350 and 12.4~18.2 for variably altered diorite and granodiorites in DBS, whereas those for DBS-TS microgabbros are 174~357 and 7.4~22, and 45.9~62.6 and 5.0~5.8 for the early Mosozoic Qz-monzonites, respectively. Zircon Eu/Eu* values are high and similar among mineralized granodiorites (~0.6), altered diorite and granodiorites (~0.6) and the Mesozoic Qz-monzonites (~0.8), whereas the values are low and variable for the DBS-TS microgabbros (0.3~0.6). The magma oxidation state calculated from zircon chemistry and whole rock compositions are FMQ +1.0 to +1.5 in mineralized samples, and FMQ +2.4 to +4.2 in altered samples. The values are comparable to those for the fertile intrusions hosting porphyry Cu-Mo-(Au) deposits in the central and western CAOB and elsewhere in the world. Elevated oxidation state is also observed in the TS microgabbros, FMQ +1.4 to +1.9, and the early Mesozoic Qz-monzonites, FMQ +2.4 to +2.5. Comparison of zircon geochemistry data from porphyry deposists elsewhere suggests that positive Ce anomalies are generally associated with fertile intrusions, but not all igneous rocks with high Ce anomalies are Cu fertile. The findings in this study are useful in exploration work and evaluating oxidation state of magmas for porphyry Cu-(Mo) deposits in the region and elsewhere.

A window on mantle-derived magmas within the Central Andes: eruption style transitions at Cerro Overo maar and La Albóndiga lava dome, northern Chile

Cerro Overo maar and La Albondiga lava dome are two independent monogenetic volcanoes located in the Central Volcanic Zone of the Andes in northern Chile, close to the active Lascar and Chiliques volcanoes. Cerro Overo maar was formed <77 ka ago by explosive-effusive eruptions, including phreatomagmatic activity, while La Albondiga lava dome (Pleistocene) is the result of magmatic explosive-effusive activity alone. Cerro Overo and La Albondiga are characterized by deposits composed of pyroclastic rocks and dense coherent lava blocks. At Cerro Overo, these deposits are located around the crater rim, while at La Albondiga, they form coherent in situ lava dome features. Cerro Overo also displays thin ash- and lapilli-dominated deposit layers presumed to be pyroclastic surge deposits, which include juvenile pyroclasts exhibiting cauliflower textures, numerous exotic accidental lithics, and ballistically transported lapilli, bombs, blocks, and bomb sags. These fragments include recycled, juvenile pyroclasts, as well as material from older volcanic and intrusive rocks from the stratigraphic units immediately below. These small-volume volcanoes represent two of the less silicic volcanoes (~54 wt.% SiO2) in the northern Chilean Pleistocene to Holocene volcanic provinces. They are characterized by a fine grain size (mainly fine lapilli), olivine phenocrysts with skeletal textures, ignimbritic, dioritic, and granitic xenoliths, and quartz xenocrysts, with high concentrations of incompatible trace elements and light rare earth elements. The general magmatic evolution of the Cerro Overo and La Albondiga systems has been controlled by fast ascent (e.g., skeletal olivine phenocrysts) of mantle-derived magma associated with mixing, fractional crystallization, and a low degree of crustal assimilation during turbulent ascent processes. Such eruptions provide evidence that various factors play an essential role in the transition from explosive-effusive magmatic (Cerro Overo and La Albondiga) to phreatomagmatic (Cerro Overo) volcanic eruption styles.