Ce and Eu anomalies in zircon as proxies for the oxidation state of magmas

http://www.geo.mtu.edu/EHaz/ConvergentPlatesClass/wallace/Grove_2006.pdf

The influence of H2O on mantle wedge melting

Isotope fractionation by chemical diffusion between molten basalt and rhyolite

Quartz and rutile were synthesized from silica-saturated aqueous fluids between 5 and 20 kbar and from 700 to 940°C in a piston-cylinder apparatus to explore the potential pressure effect on Ti solubility in quartz. A systematic decrease in Ti-in-quartz solubility occurs between 5 and 20 kbar. Titanium K-edge X-ray absorption near-edge structure (XANES) measurements demonstrate that Ti4+ substitutes for Si4+ on fourfold tetrahedral sites in quartz at all conditions studied. Molecular dynamic simulations support XANES measurements and demonstrate that Ti incorporation onto fourfold sites is favored over interstitial solubility mechanisms. To account for the P–T dependence of Ti-in-quartz solubility, a least-squares method was used to fit Ti concentrations in quartz from all experiments to the simple expression $$ RT\ln X_{{{\text{TiO}}_{ 2} }}^{\text{quartz}} = - 60952 + 1.520 \cdot T(K) - 1741 \cdot P(kbar) + RT\ln a_{{{\text{TiO}}_{ 2} }} $$
 where R is the gas constant 8.3145 J/K, T is temperature in Kelvin, $$ X_{{{\text{TiO}}_{ 2} }}^{\text{quartz}} $$
 is the mole fraction of TiO2 in quartz and $$ a_{{{\text{TiO}}_{ 2} }} $$
 is the activity of TiO2 in the system. The P–T dependencies of Ti-in-quartz solubility can be used as a thermobarometer when used in combination with another thermobarometer in a coexisting mineral, an independent P or T estimate of quartz crystallization, or well-constrained phase equilibria. If temperature can be constrained within ±25°C, pressure can be constrained to approximately ±1.2 kbar. Alternatively, if pressure can be constrained to within ±1 kbar, then temperature can be constrained to approximately ±20°C.

TitaniQ under pressure: the effect of pressure and temperature on the solubility of Ti in quartz

Evaluation of mechanical rock properties using a Schmidt Hammer

The refractory oxides MgO and Al2O3 are the most commonly used insulator/filler materials in solid-media pressure assemblies. These oxides react with one another at high temperatures and pressures, forming a well-defined layer of spinel (~MgAl2O4) at the contact. The spinel layer widens in proportion to the square root of time at a rate that also depends systematically upon temperature and pressure. On the basis of 44 piston-cylinder runs spanning 1,200–2,000 °C and 1.0–4.0 GPa, we present a general relationship describing the width (ΔX) of the spinel layer as a function of time (t, in s), temperature (T, in K) and pressure (P, in GPa): $\Delta {\rm X} = \left[ {{\rm 8}{\rm .58} \times {\rm 10}^{{\rm 11}} \cdot \exp \left( { - 48865/{\rm T} - 2.08 \cdot {\rm p}^{1/2} } \right) \cdot {\rm t}} \right]^{1/2}$ . If the pressure and duration of an experiment are known (as is usually the case) this calibration makes it possible to calculate the temperature to within a few degrees at any location in a solid-media assembly where MgO and Al2O3 are in contact (at T above ~1,200 °C) – simply by measuring the width of the spinel layer with an optical microscope. Application of this "reaction-progress" thermometer to the 13- and 19-mm diameter piston-cylinder assemblies used in the RPI lab confirms generally parabolic axial T gradients with acceptably broad hot spots. Three-dimensional maps of the 19-mm assembly reveal a radial component to the thermal field, with somewhat higher temperatures near the graphite heating element (i.e., a saddle-shaped hot region). Two exploratory experiments in a multi-anvil apparatus at 14 GPa (1,700 and 1,975 °C) confirm that the reaction-progress technique will work at pressures well above 4 GPa. The piston-cylinder-based calibration predicts ΔX to within a factor of two in the two multi-anvil runs, and relative changes in T along the assembly can be readily mapped. However, additional high-pressure calibration points will be needed before the thermometer can be used in quantitative multi-anvil applications. The spinel reaction-progress thermometer is easily implemented, and should allow other researchers to map the thermal structures of their own assemblies in a single experiment with one thermocouple.

Mapping the thermal structure of solid-media pressure assemblies

https://scholarsmine.mst.edu/cgi/viewcontent.cgi?article=1071&context=geosci_geo_peteng_facwork

Magma traps and driving pressure: consequences for pluton shape and emplacement in an extensional regime

[1] With the goal of constraining fluid and melt transport rates in the upper mantle and lower crust, various permeability–porosity relations have been proposed for deep-seated, microstructurally equilibrated rocks. Two relations that are in close agreement include one that is based on numerical modeling for an idealized rock and another that is based on direct measurement of permeability on synthetic quartzite analogs. Each relation describes a continuous increase in permeability as a function of porosity, raised to some power. The empirical relation is displaced to lower permeabilities, reflecting the more complex (nonuniform) pore geometry of the quartzites, which resembles that expected in natural, deep-seated rocks. Despite differences, the numerical models assume, and the quartzites display, a similar pore geometry that is consistent with thermodynamic equilibria: grain boundaries are “dry,” with pores largely confined to joins of three or more grains. In contrast, a fundamentally different pore microstructure, in which most of the melt occupies grain boundaries, has been proposed for partially molten dunite. This has led to the suggestion of a unique, noncontinuous, or “threshold” permeability relation for upper mantle melts. A more critical analysis of pore microstructure in dunite indicates, however, that pore shapes had been misinterpreted: very little melt is present along grain boundaries. Melt instead occupies a triple-junction network closely resembling that of the quartzite analog. Consequently, a relation similar to that for synthetic quartzites can describe upper mantle grain-scale permeabilities, because permeability is a function of pore geometry alone.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2001JB001575

Reassessment of pore shapes in microstructurally equilibrated rocks, with implications for permeability of the upper mantle

Kinetics of the reaction MgO + Al2O3 → MgAl2O4 and Al-Mg interdiffusion in spinel at 1200 to 2000°C and 1.0 to 4.0 GPa

Transient pulse decay has been widely used to measure permeability of tight rocks and synthetic materials. When the pore fluid is a gas (e.g., dry air, Ar, or N2) as used in a gas permeameter, the pressure diffusion equation governing the pulse decay problem is nonlinear due to a pressure-dependent gas compressibility and molecular slippage effect (also known as the Klinkenberg effect). To simplify data analysis in permeability measurement using a gas permeameter, an approximate solution to the nonlinear diffusion equation was obtained using a regular perturbation method. This solution, which is similar to the original exponential solution of Brace et al. [1968] for a case when the compressibility of the pore fluid is a constant, is valid in the limit when the volume of the interconnected pore fluid is much smaller than the volume of the upstream reservoir. Applications of the approximate solution to laboratory measured pulse decay data show that the estimated sample permeability can be overestimated by as much as a factor of two if the transient gas pressure decay experiment is conducted at low pressures and if molecular slippage is not taken into account. The molecular slippage can be effectively eliminated if the pulse decay measurement is conducted at a mean pressure at least 5 times higher than the Klinkenberg slip factor, which is on the order of 1 bar for texturally equilibrated marble and quartzite used in the permeability study of Wark and Watson [1998].

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000JB900344

Nonlinear pressure diffusion in a porous medium: Approximate solutions with applications to permeability measurements using transient pulse decay method

Jonathan D. Price

Papers

Mapping the thermal structure of solid-media pressure assemblies

Magma traps and driving pressure: consequences for pluton shape and emplacement in an extensional regime

Reassessment of pore shapes in microstructurally equilibrated rocks, with implications for permeability of the upper mantle

Kinetics of the reaction MgO + Al2O3 → MgAl2O4 and Al-Mg interdiffusion in spinel at 1200 to 2000°C and 1.0 to 4.0 GPa

Nonlinear pressure diffusion in a porous medium: Approximate solutions with applications to permeability measurements using transient pulse decay method