Geochimica Acta, 15, 3121-3134, O Elsevier H,O LARRIEU revisedform H 2 0 VN+ , H20 H.>0. temperature. deformatiron 10 15 above 900°C, Burnham al. the > 10 accur,ate < Ihe H20 Kerrick 1, I0 > 10 O Elsevier 1. H20 H20 solidus liquidus H20 skarn (eg, surrounding 120 McCulloch 1 ; H20 ~ble lithophile H,O H20 from equilibria. H,O \lolume Kirkwood 1 1). H20 58.5 kbars ~925'C, Burnham et Cosmochimica Vol. 61, No. pp. 1997 Copyright 1997 Science Ltd Printed in the USA. All rights reserved 0016-7037197 $17.00 + .OO Measurements of the pressure-volume-temperature properties of fluids to 20 kbar and 1000°C: A new approach demonstrated on THEODORE L. and JOHN C. AYERS Department of Geology, Vanderbilt University, Nashville, Tennessee 37235, USA (Received October 23, 1996; accepted in April 9, 1997) Abstract - A new method for measuring volumes of fluids in a piston cylinder apparatus has been from 8.5 to 20 kbar and 800" to 1000°C. A thick-walled nickel capsule partially filled with allowing it to deform until pressures inside and outside the capsule equate. Rapidly quenching the experiment preserves the capsule volume, which is measured by weighing the capsule in air and in Subtracting the known volume of the metal in the capsule from the total capsule volume yields the inner volume of the capsule, which represents the equilibrium volume of the fluid at pressure and Multiple experiments defined the conditions under which capsules are strong enough to resist on the short timescale of the quenching process, but weak enough to compact to achieve an equilibrium volume during the longer timescale of the experiment. The time required for the capsule to attain an equilibrium volume is between one and two days at 8.5 kbar and 800°C and 180 and 460 min at 1'7.5 kbar and 1000°C. Errors arising from modification of capsule volume during quenching appear minor at tested and applied to measuring the molar volume of is run at the desired pressure and temperature, kbar for temperatures up to 1000°C, but become significant at kbar for temperatures resulting in poor precision or underestimation of the equilibrium volume. The total relative error in molar volume arising from uncertainties in pressure, temperature, and volume measurement is - 2%. Measurements overlapping with those of et ( 1969) are in good agreement, suggesting method is accurate. The equation of Brodholt and Wood ( 1993) fits our data best at pressures kbar but is not at pressures 10 kbar and should be used only in combination with another equation of state accurate between zero and 10 kbar to estimate the values of integrated thermodynamic quantities. Values of fugacity of from 10- 30 kbar and 600- 1200°C calculated by combining the equations of state of and Jacobs ( 198 1 bar- kbar) and Brodholt and Wood ( 1993, kbar) are presented and fit with a polynomial to allow easy calculation of fugacity. Copyright 1997 Science Ltd INTRODUCTION even trigger deep-focus earthquakes (Meade and Jeanloz, may be respons for large- The importance of in the lower crust and upper mantle 1991 ) . Fluids containing scale transport of alkalis, ferromagnesian species, large-ion can hardly be overstated. Small weight-percentages of temperatures of rocks, elements (LILE), and rare earth elements (REE) can affect the and thereby controlling the location and extent of melting and the in the lower crust and upper mantle. potential for ascent of magma. released from intrusive magmas can trigger country rock decarbonation reactions, 1.1. Pressure - Volume - Temperature (P- V- T) Relations driving reactions such as the formation of wollastonite in of aureoles Labotka et al., 1988). Hydrothermal fluids emanating from and igneous intrusions Much of the importance of stems its ability to transport heat and dissolved constituents and may metasoma- control melting, phase stability, and mineral To tize rocks to produce ore deposits. quantify the effect of water on the physical and chemical On a larger scale, aqueous fluids are thought to be respon- properties of a system, the pressure-volume-temperature (P - sible for zonation and heterogeneity of elements in the crust V-T) relations of must be accurately known. Enthalpy, since fluids can dissolve, transport, and precipitate elements, entropy, Gibbs free energy, and fugacity values for a fluid selectively or en masse. Fluids emanating from the mantle can all be obtained by integrating the molar volume of the may metasomatize the lower crust, enriching it in trace ele- fluid over a change in pressure or temperature. infor- ments while depleting those elements in the lithospheric mation allows calculation of the dielectric constant of a fluid mantle (Eggler, 1987). In subduction zones, subducted sedi- from the Equation. ments dehydrate continuously to depths greater than km, Figure is a P - T diagram showing lines of equal volume and the liberated fluid may migrate into the overlying mantle (isochores) in the supercritical fluid region for pressures wedge, transporting major and trace elements and pro- extending up to 30 kbar and temperatures up to 1500°C (Fig. foundly affecting island arc magmatism (Plank and Lang- The P- V- T properties of are well known only at muir, 1993; and Gamble, 199 and temperatures primarily Hydrous mineral dehydration in the subducting slab may because et al. (1969) made many high-accuracy Eggler, 1989). pressures