UV laser radiation for microstructuring of photostructurable glasses

Photostructurable glasses are important materials for applications in microsystems. They enable structures with high aspect ratios and a high dependability of mechanical, optical and chemical properties in a large range of temperatures. The exposure of photostructurable glasses to UV laser radiation, as a rapid prototyping technique, is an alternative method to the exposure by a mask aligner. Α photostructurable glass (FS21) was exposed to UV laser radiation of the wavelengths 248, 308 and 355 nm. Investigated was the influenee of the exposure parameters wavelength of laser radiation and energy density on structuring results such as crystallization depth, lateral geometry of crystallized areas, structure of crystallized areas and etch angle for single pulse exposure

Magma mixing enhanced by bubble segregation

In order to explore the materials' complexity induced by bubbles rising through mixing magmas, bubble-advection experiments have been performed, employing natural silicate melts at magmatic temperatures. A cylinder of basaltic glass was placed below a cylinder of rhyolitic glass. Upon melting, bubbles formed from interstitial air. During the course of the experimental runs, those bubbles rose via buoyancy forces into the rhyolitic melt, thereby entraining tails of basaltic liquid. In the experimental run products, these plume-like filaments of advected basalt within rhyolite were clearly visible and were characterised by microCT and high-resolution EMP analyses. The entrained filaments of mafic material have been hybridised. Their post-experimental compositions range from the originally basaltic composition through andesitic to rhyolitic composition. Rheological modelling of the compositions of these hybridised filaments yield viscosities up to 2 orders of magnitude lower than that of the host rhyolitic liquid. Importantly, such lowered viscosities inside the filaments implies that rising bubbles can ascend more efficiently through pre-existing filaments that have been generated by earlier ascending bubbles. MicroCT imaging of the run products provides textural confirmation of the phenomenon of bubbles trailing one another through filaments. This phenomenon enhances the relevance of bubble advection in magma mixing scenarios, implying as it does so, an acceleration of bubble ascent due to the decreased viscous resistance facing bubbles inside filaments and yielding enhanced mass flux of mafic melt into felsic melt via entrainment. In magma mixing events involving melts of high volatile content, bubbles may be an essential catalyst for magma mixing. Moreover, the reduced viscosity contrast within filaments implies repeated replenishment of filaments with fresh end-member melt. As a result, complex compositional gradients and therefore diffusion systematics can be expected at the filament-host melt interface, due to the repetitive nature of the process. However, previously magmatic filaments were tacitly assumed to be of single-pulse origin. Consequently, the potential for multi-pulse filaments has to be considered in outcrop analyses. As compositional profiles alone may remain ambiguous for constraining the origin of filaments, and as 3-D visual evidence demonstrates that filaments may have experienced multiple bubbles passages even when featuring standard diffusion gradients, therefore, the calculation of diffusive timescales may be inadequate for constraining timescales in cases where bubbles have played an essential role in magma mixing. Data analysis employing concentration variance relaxation in natural samples can distinguish conventional single-pulse filaments from advection via multiple bubble ascent advection in natural samples, raising the prospect of yet another powerful application of this novel petrological tool

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

Europium structural role in silicate glasses: reduction kinetics at low oxygen fugacity.

This study is focused on the determination of the geochemical behaviour of europium (Eu) in a set of synthetic silicate glasses with composition relevant for the Earth Science and ranging from basaltic to granitic composition. The samples have been characterized through Eu L-III-edge by X-ray Absorption Spectroscopy (XAS) and the measurements have been performed in fluorescence mode at the ESRF (Grenoble, F). Eu L-III-edge XANES analysis allowed to obtain a semi-quantitative assessment of the Eu2+/(Eu2+ + Eu3+) redox ratio. Kinetics of europium reduction at low oxygen fugacity (IW buffer) has been studied on samples equilibrated at different times. Data obtained from kinetic experiments clearly show that glasses of basaltic composition reach equilibrium values of the Eu2+/(Eu2+ + Eu3+) ratio after 6 h at 1400 degrees C, whereas glasses of granitic composition reach equilibrium after 60 h at 1400 degrees C. Knowledge of Eu reduction kinetics is an absolute prerequisite for any study of Eu oxidation state at low oxygen fugacity

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

Europium oxidation state and local structure in silicate glasses

Europium LIII-edge XAS spectra were recorded for silicate glasses of different compositions, quenched from melts equilibrated at different oxygen fugacity (fO2). The Eu XANES spectra vary systematically with glass composition and with fO2 (–log fO2 ~0 to ~11.9) indicating changes in the Eu oxidation state. The intensity of the main peaks on the absorption edges were quantified and used to determine the Eu2+/(Eu2++Eu3+) ratio. All the Eu-bearing glasses synthesized in air show the prevalent presence of Eu3+ but also, unexpectedly, the presence of a small amount of Eu2+ in the basaltic glasses and up to 20% of Eu2+ in the haplogranitic sample. Moreover, XANES analyses of the samples synthesized at reducing conditions (from FMQ to IW-2) show that europium in haplogranitic glasses is always more reduced than in basaltic glasses. No relationship has been found between Eu valence and alkali content in the studied glasses. The structural environment of Eu in the glasses was determined by EXAFS analyses, demonstrating the different Eu behavior as function of the fO2. In fact, in air, Eu3+ both for basaltic and haplogranitic compositions, is bonded to six O atoms in a regular octahedron (CN = [6 ± 0.5]) with similar distances of about 2.30 ± 0.02 Å. On the other hand, the almost purely divalent samples have Eu2+ in a higher coordination (CN = [9 ± 1]) and longer distances (2.68 ± 0.02 Å). This work clearly demonstrates that, in addition to oxygen fugacity, melt composition also plays a strong role in affecting Eu oxidation state. Moreover, for the first time, experimentally derived structural data of Eu2+ in silicate glasses of geological interest are presented. Keywords: Europium, oxidation state, silicate glasses structure, XA

Experimental study of monazite solubility in haplogranitic melts: a new model for peraluminous and peralkaline melts

Abstract: Monazite is a common accessory mineral in peraluminous, metaluminous and peralkaline granitic/rhyolitic rocks. Considering the importance of monazite in geochemical and geochronological studies, a monazite solubility model that can be applied to a wide compositional range of magmas is desirable. To accomplish this, monazite solubility experiments were performed at atmospheric (1400 C) and crustal pressures (1–3 kbar, 720–850 C, H2O-saturated), using haplogranitic compositions ranging from peraluminous to peralkaline, doped with synthetic pure LaPO4. The concentrations of La in the melts increase sharply with increasing temperature and peralkalinity of the melt. We combined our new data with those of previous studies to describe the solubility of monazite in peralkaline to peraluminous melts. Our new monazite saturation model, which incorporates temperature, pressure, water content, melt and monazite composition is given by: lnRLREE = 12.77(±0.49) + 1.52(±0.15)M + 22 0.44(±0.10)(H2O)0.5 9934(±632)/T 36.79(±6.15)P/T + lnXLREE mnz where RLREE is the sum of the concentrations of La to Sm in monazite-saturated melt, in ppm, M is a dimensionless compositional parameter (Na + K + 2Ca) · Al1 · (Al + Si)1, similar to the compositional parameter used in an earlier model by Montel; Na, K, Ca, Al, Si are in moles, H2O is water content in weight percent, T is the temperature in K, P is the pressure in kbar, and XLREE mnz is the mole fraction of LREE in monazite LREEmnz/ (LREEmnz + Ymnz + Thmnz + Umnz). This model reproduces 76% and >95% of the data to within uncertainties of ±10% and ±20%, respectively. It may be applied to felsic melts poor in CaO + FeO + MgO (<3 wt%) from peraluminous to peralkaline compositions. Key-words: monazite; solubility; melt composition; agpaitic index; peralkaline; peraluminous; haplogranite; model; experimental petrology

Raman spectra of Martian glass analogues: A tool to approximate their chemical composition

International audienceRaman spectrometers will form a key component of the analytical suite of future planetary rovers intended to investigate geological processes on Mars. In order to expand the applicability of these spectrometers and use them as analytical tools for the investigation of silicate glasses, a database correlating Raman spectra to glass composition is crucial. Here we investigate the effect of the chemical composition of reduced silicate glasses on their Raman spectra. A range of compositions was generated in a diffusion experiment between two distinct, iron-rich end-members (a basalt and a peralkaline rhyolite), which are representative of the anticipated compositions of Martian rocks. Our results show that for silica-poor (depolymerized) compositions the band intensity increases dramatically in the regions between 550-780 cm À1 and 820-980 cm À1. On the other hand, Raman spectra regions between 250-550 cm À1 and 1000-1250 cm À1 are well developed in silica-rich (highly polymerized) systems. Further, spectral intensity increases at ~965 cm À1 related to the high iron content of these glasses (~7-17 wt % of FeO tot). Based on the acquired Raman spectra and an ideal mixing equation between the two end-members we present an empirical parameterization that enables the estimation of the chemical compositions of silicate glasses within this range. The model is validated using external samples for which chemical composition and Raman spectra were characterized independently. Applications of this model range from microanalysis of dry and hydrous silicate glasses (e.g., melt inclusions) to in situ field investigations and studies under extreme conditions such as extraterrestrial (i.e., Mars) and submarine volcanic environments