Non-Newtonian Rheology of Igneous Melts at High Stresses and Strain Rates: Experimental Results for Rhyolite, Andesite, Basalt, and Nephelinite

The stress-strain rate relationships of four silicate melt compositions (high-silica rhyolite, andesite, tholeiitic basalt, and nephelinite) have been studied using the fiber elongation method. Measurements were conducted in a stress range of 10–400 MPa and a strain rate range of 10−6 to 10−3 s−1. The stress-strain rate relationships for all the melts exhibit Newtonian behavior at low strain rates, but non-Newtonian (nonlinear stress-strain rate) behavior at higher strain rates, with strain rate increasing faster than the applied stress. The decrease in calculated shear viscosity with increasing strain rate precedes brittle failure of the fiber as the applied stress approaches the tensile strength of the melt. The decrease in viscosity observed at the high strain rates of the present study ranges from 0.25 to 2.54 log10 Pa s. The shear relaxation times τ of these melts have been estimated from the low strain rate, Newtonian, shear viscosity, using the Maxwell relationship τ = η s /G ∞. Non-Newtonian shear viscosity is observed at strain rates ( ɛ ˙ = time - 1 ) equivalent to time scales that lie 3 log10 units of time above the calculated relaxation time. Brittle failure of the fibers occurs 2 log10 units of time above the relaxation time. This study illustrates that the occurrence of non-Newtonian viscous flow in geological melts can be predicted to within a log10 unit of strain rate. High-silica rhyolite melts involved in ash flow eruptions are expected to undergo a non-Newtonian phase of deformation immediately prior to brittle failure

Structural relaxation in silicate melts and non-Newtonian melt rheology in geologic processes

The timescale of structural relaxation in a silicate melt defines the transition from liquid (relaxed) to glassy (unrelaxed) behavior. Structural relaxation in silicate melts can be described by a relaxation time, , consistent with the observation that the timescales of both volume and shear relaxation are of the same order of magnitude. The onset of significantly unrelaxed behavior occurs 2 log10 units of time above . In the case of shear relaxation, the relaxation time can be quantified using the Maxwell relationship for a viscoelastic material; S = S/G (where S is the shear relaxation time, G is the shear modulus at infinite frequency and S is the zero frequency shear viscosity). The value of G known for SiO2 and several other silicate glasses. The shear modulus, G , and the bulk modulus, K , are similar in magnitude for every glass, with both moduli being relatively insensitive to changes in temperature and composition. In contrast, the shear viscosity of silicate melts ranges over at least ten orders of magnitude, with composition at fixed temperature, and with temperature at fixed composition. Therefore, relative to S, G may be considered a constant (independent of composition and temperature) and the value of S, the relaxation time, may be estimated directly for the large number of silicate melts for which the shear viscosity is known. For silicate melts, the relaxation times calculated from the Maxwell relationship agree well with available data for the onset of the frequency-dependence (dispersion) of acoustic velocities, the onset of non-Newtonian viscosities, the scan-rate dependence of the calorimetric glass transition, with the timescale of an oxygen diffusive jump and with the Si-O bond exchange frequency obtained from 29Si NMR studies. Using data obtained over a range of frequencies and strain-rates we illustrate the significance of relaxed versus unrelaxed behavior in laboratory experiments on silicate melts. Similarly, using strain-rate estimates for magmatic processes we evaluate the significance of the liquid-glass transition in igneous petrogenesis. Dedicated to the memory of Chris Scarf

The onset of non-Newtonian rheology of silicate melts

The viscoelastic behavior of silicate melts has been measured for a range of compositions (NaAlSi3O8, NaCaAlSi2O7, CaMgSi2O6, Li2Si4O9, Na2Si4O9, K2Si4O9, Na2Si3O7, K2Si3O7 and Na2Si2O5) using the fiber elongation method. A1l compositions exhibit Newtonian behavior at low strain-rates, but non-Newtonian behavior at higher strain-rates, with strain-rate increasing faster than the applied stress. The decrease in shear viscosity observed at the high strain-rates ranges from 0.3 to 1.6 log10 units (Pa s). The relaxation strain-rates, relax, of these melts have been estimated from the low strain-rate, Newtonian, shear viscosity, using the Maxwell relationship; relax= –1=(s/G)–1. For all compositions investigated, the onset of non-Newtonian rheology is observed at strain-rates 2.5+0.5 orders of magnitude less than the calculated relaxation strain-rate. This difference between the non-Newtonian onset and the relaxation strain-rate is larger than that predicted by the single relaxation time Maxwell model. Normalization of the experimental strain-rates to the relaxation strain-rate predicted from the Maxwell relation, eliminates the composition. and temperature-dependence of the onset of non-Newtonian behavior. The distribution of relaxation in the viscoelastic region appears to be unrelated to melt chemistry. This conclusion is consistent with the torsional, frequency domain study of Mills (1974) which illustrated a composition-invariance of the distribution of the imaginary component of the shear modulus in melts on the Na2O-SiO2 join. The present, time domain study of viscoelasticity contrasts with frequency domain studies in terms of the absolute strains employed. The present study employs relatively large total strains (up to 2). This compares with typical strains of 10–8 in ultrasonic (frequency domain) studies. The stresses used to achieve the strain-rates required to observe viscoelastic behavior in this study approach the tensile strength of the fibers with the result that some of our experiments were terminated by fiber breakage. Although the breakage is unrelated to the observation of non-Newtonian viscosity, their close proximity in this and earlier studies suggests that brittle failure of igneous melts, may, in general, be preceded by a period of non-Newtonian rheology

The fluxing effect of fluorine at magmatic temperatures (600-800 °C): A scanning calorimetric study

The effect of F on the glass transition behavior of albite, diopside, and four other silicate melts has been investigated using scanning calorimetry. The addition of F to all silicate melts investigated results in a strong, nonlinear decrease of the glass transition temperature (Z' as recorded by the peak temperatures of heat capacity). The decreases observed extrapolate consistently to published fluoride glass transition temperatures. The largest Z, decrease is observed for albite-FrO-, melts (AT = 250 °C at 6 wt%F ). The effect of F is similar to that previously observed for HrO (Taniguchi, 1981). Physical properties of low-temperature silicate liquids are a valuable constraint on lowtemperature petrogenetic processes in granite and pegmatite petrogenesis. Low-temperature wiscosities can be estimated from the glass transition data. These data are combined with previously published high-temperature, concentric-cylinder viscosity data to obtain a much more complete description of the temperature dependence of viscosity for these melts. The present data, obtained on supercooled liquids close to the glass transition, are of special significance because it is at the glass transition that silicate glass structures are frozen. A separate multinuclear NMR study of glasses quenched from these experiments has shown that the predominant coordination of F in albite glass is octahedral to Al. The coordination state of F does not appear to be concentration dependent, and thus the structural origin of the nonlinear Z, decrease does not arise from such a mechanism

A consideration of copyright for a national repository of humanities and social science data

In 2011 the Digital Repository of Ireland (DRI) began work on the development of an interactive national Trusted Digital Repository for contemporary and historical social and cultural data. Copyright and intellectual property rights were identified as essential areas which the DRI, as a content holder and data publisher, needed to investigate in order to develop workflows, policy and the Repository infrastructure. We established a Copyright and IP Task Force (CIPT) in January 2013 to capture and identify IP challenges from our stakeholder community and the DRI’s demonstrator collections. This report outlines the legislative context in which the CIPT worked, and how the CIPT addressed copyright challenges through the development of policies and a robust framework of legal documentation for the Repository. We also provide a case study on Orphan Works, detailing the process undertaken by the Clarke Stained Glass Studios Collection, one of DRI’s demonstrator projects, in preparing their content for online publication in the Repository

“Reconfiguring Narrative” Using Digital Tools

This article describes the use of digital technology and text markup in the production and dissemination of scholarship. Traditional narrative, as static, linked arguments and paragraphs reflect the constraints, limitations but important use of print technology. “Reconfiguring the narrative” to reflect the capabilities of online scholarship enables readers and writers to engage in more thorough explorations of the text, theory, concepts, and interpretations (Landow, 2006)

The effect of F on the density of haplogranite melt

The densities and thermal expansivities of F-bearing haplogranitic glasses and liquids have been investigated using a combination of scanning calorimetry and dilatometry. F2O-1 reduces the density of haplogranitic liquids (at 750 °C) from 2.295 + 0.006 g/cm3 to 2.261 + 0.005 g/cm3 with the addition of 4.55 wt% F (0.33% per wt% of F added). The expansivities of the liquids increase with the addition of F2O-1 from 29.9 +- 3.0 x l0 -6/°C to 53.1 +- 1.4 x l0 -6/°C (at 750°C). Densities have been converted into molar volumes based on the haplogranite and F2O-1 components. The partial molar volume of F2O-1 has been calculated at 750°C to be 14.2 +- 1.3 cm3/mol in these melts. This value is close to the molar volume per O for several components of silicate melts. F and O have similar ionic and covalent radii, and thus the substitution of two F for one O yields approximately the volume change expected, assuming no secondaryc onsequencesfo r the averagec oordination number of cations. This is despite evidence from quenched melts that [6]Al exists in these compositions. F is significantly more effective (per wt% added) than B2O3 in reducing the density of haplogranitic melt. The effect of F on density reported here should complement the viscosity- reducing effect of F2O-1 on granitic melts in significantly acceleratingg ravity-driven processes of crystal-melt fractionation in F-rich igneous systems

Determination of silicate liquid thermal expansivity using dilatometry and calorimetry

A method for the determination of relaxed silicate liquid molar volume and expansivity at temperatures just above the glass transition is discussed. The method involves the comparison of heat capacity and molar expansivity in the glass transition region. Glassy and liquid heat-capacity data are obtained using differential scanning calorimetry, and glassy thermal expansion data are obtained using scanning dilatometry. The molar expansivity of the liquid is calculated by a fictive temperature normalization of the relaxation behavior of both the heat capacity and the molar expansivity in the glass transition region, with the normalized heat capacity curve being used to extend the dilatometric data into the liquid temperature range. This comparison is based upon the assumed equivalence of the parameters describing the relaxation of volume and enthalpy. The molar expansivity of relaxed sodium trisilicate (Na2Si3O7) has been determined in this manner at temperatures above the glass transition temperature. This low-temperature determination of liquid molar expansivity has been tested against high-temperature liquid expansivity data obtained from high temperature Pt double bob Archimedean buoyancy measurements. The low-temperature molar expansivity (26.43±0.83xl0~4 cm3 mole"lßC_1 at 540°C) determined in this manner agrees within error with the high-temperature molar expansivity (23.29±1.39xl0~4 cm3 mole^ºC1 at 1400°C). This dilatometric/calorimetric method of liquid molar expansivity determination greatly increases the temperature range accessible for thermal expansion measurements. A weighted linear fit to the combined low and high temperature volume data gives a molar expansivity of 23.0010.25x10^ cm3 mole^ºC"1. The volume-temperature relationship thus derived reproduces the measured volumes from both dilatometry and densitometry with a RMSD value of 0.033 cm3 mole"1 or 0.14%. This represents a substantial increase in precision, which is especially important for liquids whose high liquidus temperatures restrict the temperature range accessible to liquid volume determinations

The effect of P2O5 on the viscosity of haplogranitic liquid

The effect of P2O5 on the viscosity of a haplogranitic (K2O-Na2O-Al2O3-SiO2) liquid has been determined at 1 atm pressure in the temperature interval of 700 - 1650°C. Viscosity measurements of a haplogranite, haplogranite + 5.1 wt.% P2O5 and haplogranite + 9.5 wt.% P2O5 have been performed using the concentric cylinder and micropenetration methods. The viscosity of haplogranite liquid decreases with the addition of P2O5 at all temperatures investigated. The viscosity decrease is nonlinear, with the strongest decrease exhibited at low P2O5 concentration. The temperature-dependence of the viscosity of all the investigated liquids is Arrhenian, as is the case for P2O5 liquid. The Arrhenian activation energy is slightly lower in the P2O5-bearing liquids than in the P2O5-free haplogranite with the result that the effect of P2O5 on viscosity is a (weak) function of temperature. At temperatures corresponding to the crystallization of phosphorus-rich granitic and pegmatitic systems the addition of 1 wt.% of P2O5 decreases the viscosity 0.2 log10 units. The effect of P2O5 on haplogranitic melt viscosity is much less than that for B2O3, F2O−1 on the same melt composition (Dingwell et al., 1992 and this study). This implies that P2O5 concentration gradients in high-silica melts during, for example, phosphate mineral growth or dissolution in granitic magmas, will not significantly influence melt viscosity