I-Ming Chou, 954 National Center, U.S. Geological Survey, Reston, VA 20192, U.S.A.

imchou@usgs.gov

Introduction

The hydrothermal diamond-anvil cell (HDAC) was designed specifically for the study of geologic material under hydrothermal conditions, even though the applicable P-T range of the cell is much larger; pressures range up to 10 GPa and temperatures span –190 and 1200° C (Bassett et al., 1993). It should be emphasized that the main application of the HDAC is for the study of geologic processes in the crust in the presence of water or other fluids, and, as contrast to the traditional diamond anvil cell, it is not for the studies of Earth mantle or core (Hemley and Ashcroft, 1998). Haselton and Chou (1994) constructed a control and data acquisition system for the HDAC. Chou et al. (1994) described the applications of the HDAC in fluid-inclusion related research, and Bassett et al. (1996) and Li (1999) reviewed general applications of the HDAC. Recently, the HDAC was modified for the study of gigahertz ultrasonic interferometry and X-ray diffraction for single crystals (Bassett et al., 2000a), and also for collecting XAFS (X-ray absorption fine structure) spectra of supercritical aqueous solutions (Bassett et al., 2000b; Bassett, 2000).

The advantages of the HDAC for hydrothermal studies include: (1) widely applicable P-T range, (2) low cost, (3) safe operation, (4) ease of loading samples, (5) allowance of in-situ sample characterization through optical observation and spectroscopic analysis, including Raman, FTIR, and synchrotron X-ray, (6) ease of keeping permanent records on video tapes, and (7) capability of varying bulk sample density without reloading.

Major recent applications of the HDAC include: (1) the acquisition of equation of state for geologic fluids (Shen et al., 1993a, 1993b, 1994; Shen, 1994) and minerals (Wu et al., 1995), (2) characterization of a new H₂O ice phase (Chou et al., 1998) and a new methane hydrate phase (Chou et al., 2000), and determination of their respective melting relations, (3) microthermometric analysis of high-density fluid inclusions (Schmidt et al., 1998; Darling and Bassett, 2000), (4) study of melting relations in the aqueous systems containing silicate (Shen and Keppler, 1995a; Chou and Anderson, 1998; Anderson and Chou, 1999, 2000, Shen et al., 2000; Sowerby and Keppler, 2000), carbonate (Cooper et al., 1998), and hydroxide (Chou et al., 1995), (5) calibration of pressure calibrants (Chou et al., 1993; Chou and Nord, 1993, 1994; Chou and Haselton, 1994; Haselton et al., 1995; Schmidt and Ziemann, 2000, in press), (6) studying ion-paring in hydrothermal solutions by Raman scattering (Frantz et al., 1994), (7) infrared spectroscopy of hydrous silicate melts (Shen and Keppler, 1995b), and aqueous NaCl solutions (Hu and Zhang, 2000), (8) determination and characterization of hydration and dehydration of clays using synchrotron radiation (Huang et al., 1994; Wu et al., 1997), and (9) study of organic material (Huang and Otten, 2000, Chou et al., 2000, Sharma et al., 2000).

Recently, the HDAC has been modified to study gigahertz ultrasonic interferometry and X-ray diffraction for single crystals (Bassett et al., 2000a). However, the most exciting development is that two other modifications have been made on the HDAC by machining the diamonds using Q-switched YAG laser: (1) "holy" diamonds, suitable for transmission XAFS (Bassett et al., 2000b), and (2) "groovy" diamonds, suitable for fluorescence XAFS (Bassett, 2000). In both modified cells, the loss of intensity of X-ray due to scattering and absorption by the diamonds was minimized by removing as much solid material as possible along the path of the X-ray beam. As a result, excellent XAFS spectra can be obtained for first-row transition elements in aqueous solutions, up to supercritical conditions (Bassett et al., 2000b; Bassett, 2000, Mayanovic et al., 1999a, 1999b, 2000). This will provide the basic information on speciation and structure of metal complexes in hydrothermal solutions, to facilitate our understanding of not only the transportation and deposition of elements in geologic systems (Seward and Barnes, 1997; Anderson et al., 1998), but also the fundamental physicochemical properties of aqueous solutions at elevated P-T conditions.

It has been demonstrated that the HDAC is a very versatile new tool for gathering fundamental information related to geologic processes under hydrothermal conditions. Allowing in-situ observation and sample characterization under elevated P-T conditions in the HDAC experiments, not only eliminates the problems related to the quenching processes, which are commonly encountered in the conventional hydrothermal experiments, but also creates opportunities to discover unexpected phases and phenomena.

I would like to thank all of my previous coauthors on this subject, especially William A. Bassett (Cornell University, USA), Andy H.T. Shen (University of Cambridge, UK), Alan J. Anderson (St. Francis Xavier University, Canada), Robert A. Mayanovic (Southwest Missouri University, USA), and H. T. Haselton, Jr. for the exciting development of this technique.

Anderson, A.J., Mayanovic, R.A., and Chou, I.M., 1998, Micro-beam XAFS measurements of zinc complexes in highly saline fluid inclusions to 400° C before and after experimental re-equilibration at high hydrogen pressure. Goldschmidt Conference, Toulouse, France. Mineralogical Magazine, v. 62A, p. 55-56.

Anderson, A.J., and Chou, I.M., 1999, Direct observation of crystallization in the system NaAlSi₃O₈-SiO₂-LiAlSiO₄-H₂O using the hydrothermal diamond anvil cell: Insights into the formation of gem pockets in miarolitic pegmatites. Joint Annual Meeting of Geological Association of Canada and Mineralogical Association of Canada, May 26-28, 1999, Sudbury, Canada, v. 24, p. 2.

Anderson, A. J., and Chou, I., 2000, Direct observation of bubble nucleation in rhyolitic melts in response to reductions in pressure and temperature. American Geophysical Union Transactions, v. 81, p. S36-37.

Bassett, W.A., Shen, A.H., Bucknum, M., and Chou, I. M., 1993, A new diamond anvil cell for hydrothermal studies to 10 GPa and -190° C to 1100° C: Reviews of Scientific Instruments, v. 64 (8), p. 2340-2345.

Bassett, W.A., Wu, T.C., Chou, I.M., Haselton, H.T., Jr., Frantz, J., Mysen, B.O., Huang, W.L., Sharma, K., and Schiferl, D., 1996, The hydrothermal diamond anvil cell (HDAC) and its applications. In: "Mineral Spectroscopy: A Tribute to Roger G. Burns", M.D. Dyar, C. McCammon, and M.W., Schaefer eds., The Geochemical Society Special Publication No. 5, p. 261-272.

Bassett, W.A., Reichmann, H.-J., Angel, R.J., Spetzler, H., and Smyth, J.R., 2000a, New diamond anvil cells for gigahertz ultrasonic interferometry and X-ray diffraction. American Mineralogist, v. 85, p. 283-287.

Bassett, W.A., Anderson, A.J., Mayanovic, R.A., and Chou, I.M., 2000b, Hydrothermal diamond anvil cell for XAFS studies of first-row transition elements in aqueous solution up to supercritical conditions. Chemical Geology, v. 167, p. 3-10.

Bassett, W.A., 2000, Holy and groovy diamonds, the latest in diamond anvil cells. American Geophysical Union Transactions, v. 81, p. S36.

Chou, I.M., Haselton, H.T., Jr., Nord, G.L., Jr. Shen, A.H., and Bassett, W.A., 1993, Barium titanate as a pressure calibrant in the diamond anvil cell: American Geophysical Union Transactions, v. 74, no. 16, p. 170.

Chou, I.M., and Nord, G.L., Jr., 1993, Observation of a /b cristobalite transition under hydrostatic pressures in diamond-anvil cell: GSA Abstracts with Programs, v. 25, no. 6, p. A-147.

Chou, I.M., and Haselton, H.T., Jr., 1994, Lead titanate as a pressure calibrant in the diamond anvil cell. Abstracts, 16th General Meeting, IMA, p. 74-75.

Chou, I.M., and Nord, G.L., Jr., 1994, Lead phosphate as a pressure calibrant in the hydrothermal diamond-anvil cell. GSA Abstracts with Programs, v. 26, no. 7, p. A-291.

Chou, I.M., Shen, A.H., and Bassett, W.A., 1994, Applications of the hydrothermal diamond-anvil cells in fluid-inclusion research, in De Vivo, B., and Frezzotti, M.L., ed., Fluid Inclusions in Minerals: Methods and Applications. Short course of the working group (IMA) "Inclusions in Minerals", p. 215-230.

Chou, I.M., Bassett, W.A., and Bai, T.B., 1995, Hydrothermal diamond-anvil cell study of melts: Eutectic melting of the assemblage Ca(OH)₂-CaCO₃ with excess H₂O and lack of evidence for "portlandite II" phase: American Mineralogist, v. 80, P. 865-868.

Chou, I.M., and Anderson, A.J., 1998, Direct observation of low temperature melting in the system petalite-quartz-H₂O using a hydrothermal diamond-anvil cell: methods and geological implications. Goldschmidt Conference, Toulouse, France. Mineralogical Magazine, v. 62A, p. 327-328.

Chou, I.M., Blank, J.G., Goncharov, A.F., Mao, H.K., and Hemley, R.J., 1998, In situ observations of a high-pressure phase of H₂O ice. Science, v. 281, p. 809-812.

Chou, I.M., Burruss, R.C., Goncharov, A.F., Sharma, A., Hemley, R.J., Stern, L.A. and Kirby, S.H., 2000, In situ observations of a new high-pressure methane hydrate phase. American Geophysical Union Transactions, v. 81, p. S38.

Cooper, A., Wood, B.J., and Ragnarsdottir, K.V., 1998, The properties of carbonated fluids in the system Na₂CO₃-H₂O and K₂CO₃-H₂O to 1000° C and 20 kbar. Goldschmidt Conference, Toulouse, France. Mineralogical Magazine, v. 62A, p. 347-348.

Darling, R.S., and Bassett, W.A., 2000, Analysis of H₂O+CO₂+NaCl fluid inclusions in the hydrothermal diamond anvil cell. American Geophysical Union Transactions, v. 81, p. S39.

Frantz, J.D., Dubessy, J., and Mysen, B.O., 1994, Ion-pairing in aqueous MgSO₄ solutions along an isochore to 500° C and 11 kbar using Raman spectroscopy in conjunction with the diamond-anvil cell. Chemical Geology, v. 116, p. 181-188.

Haselton, H.T., Jr., and Chou, I.M., 1994, A control and data acquisition system for use with a hydrothermal diamond-anvil cell. U.S. Geological Survey Open-file Report 94-703, 23p.

Haselton, H.T., Jr., Chou, I.M., Shen, A.H., and Bassett, W.A., 1995, Techniques for determining pressure in the hydrothermal diamond-anvil cell: The behavior of ice polymorphs (I, III, V, VI): American Mineralogist, v. 80, p. 1302-1306.

Hemley, R.J., and Ashcroft, N.W, 1998, The revealing role of pressure in the condensed

matter sciences. Physics Today, v.51, p. 26-32.

Hu, Shumin, and Zhang Ronghua, 2000, A study of aqueous solutions at elevated temperatures and pressures using hydrothermal diamond anvil cell and in situ FT-IR spectroscopy. (this volume).

Huang, W.L, Bassett, W.A., and Wu, T.C., 1994, Dehydration and hydration of montmorillonite at elevated temperatures and pressures monitored using synchrotron radiation. American Mineralogist, v. 79, p. 683-691.

Huang, W., and Otten, G.A., 2000, Fluorescence behavior of crude oils and alkanes during cracking monitored in situ at elevated temperatures and pressures. American Geophysical Union Transactions, v. 81, p. S38.

Li, Zhao-lin, 1999, Application of hydrothermal diamond anvil cell to geology and the experiment in synthesis of methane hydrates. Earth Science Frontiers (China University of Geosciences, Beijing), v. 7, no. 1, p. 271-285.

Mayanovic, R.A., Anderson, A.J., Bassett, W.A., and Chou, I.M., 1999a, XAFS measurements on zinc chloride aqueous solutions from ambient to supercritical conditions using the diamond anvil cell. Journal of Synchrotron Radiation, v. 6, p. 195-197.

Mayanovic, R.A., Anderson, A.J., Bassett, W.A., and Chou, I.M., 1999b, XAFS investigations of aqueous zinc halide solutions up to supercritical conditions. Final Program and Abstracts, 13^th International Conference on the Properties of Water and Steam. Toronto, Canada, September 12-16, p.77.

Mayanovic, R. A., Anderson, A.J., Bassett, W.A., and Chou, I., 2000, Evidence for dehydration of zinc halide complexes from XAFS measurements on zinc bromide and zinc chloride aqueous solutions at up to 500° C and elevated pressures using a hydrothermal diamond anvil cell. American Geophysical Union Transactions, v. 81, p. S37.

Schmidt, C., Chou, I.M., Bodnar, R.J., and Bassett, W.A., 1998, Microthermometric analysis of synthetic fluid inclusions in the hydrothermal diamond-anvil cell. American Mineralogist. v. 83, p. 995-1007.

Schmidt, C., and Ziemann, M.A., 2000, In-situ Raman spectroscopy of quartz at crustal P-T conditions: A pressure sensor for hydrothermal diamond-anvil cell studies. American Geophysical Union Transactions, v. 81, p. S37.

Schmidt, C. and Ziemann, M.A., (in press), In-situ Raman spectroscopy of quartz: A pressure sensor for hydrothermal diamond-anvil cell experiments at elevated temperatures. American Mineralogist.

Seward, T.M., and Barnes, H.L. 1997, Metal transport by hydrothermal ore fluids. In: Geochemistry of hydrothermal ore deposits. 3rd ed. H.L. Barnes (ed.). New York John Wiley & Sons, Inc. 435- 486.

Sharma, A., Cody, G.D., Goncharov, A., Hazen, R.M., Hemley, R.J., Mao, H., and Chou, I., 2000, Direct observations on the hydrothermal organic synthesis reactions with implications on CO₂ phase behavior at high pressure and temperature. American Geophysical Union Transactions, v. 81, p. S38.

Shen, A.H., Chou, I.M., and Bassett, W.A., 1993a, Experimental determination of isochores of H₂O in a diamond-anvil cell up to 1200 MPa and 860° C with preliminary results in the NaCl-H₂O system. Proceedings of the 4th International Symposium on Hydrothermal Reactions, p. 235-239.

Shen, A.H., Bassett, W.A., and Chou, I.M., 1993b, The a -b quartz transition observed at simultaneous high temperatures and high pressures in a diamond-anvil cell by laser interferometry: The American Mineralogist, v. 78, p. 694-698.

Shen, A.H., Chou, I.M., and Bassett, W.A., 1994, Experimental determination of PVTX relations of fluids in the diamond-anvil cell (V.M. Goldschmidt Conference, Edinburgh). Mineralogical Magazine, v. 58A, p. 823-824.

Shen, A.H., 1994 - PhD thesis, Hydrothermal studies in the diamond-anvil cell: pressure-volume-temperature-composition relations of water and aqueous sodium chloride solutions to 12 kbar and 850 degree centigrade, Department of Geological Sciences, Cornell University, Ithaca, NY 14853, U.S.A., available from UMI Dissertation Services, A Bell & Howell Company, 300 N. Zeeb Road, Ann Arbor, Michigan 28106, U.S.A.

Shen, A., and Keppler, H., 1995a,Direct observations of supercritical behaviour in albite-H₂O system. Nature, v. 358, p. 710-714.

Shen, A., and Keppler, H., 1995b, Infrared spectroscopy of hydrous silicate melts to 1000 ° C and 10 kbar: Direct observation of H₂O speciation in a diamond-anvil cell, American Mineralogist, v. 80, p. 1335-1338.

Shen, A.H., Hammon, L.T., and Zheng, H., 2000, Direct observation of dehydration of melts in the K₂O-SiO₂-CO₂-H₂O system. American Geophysical Union Transactions, v. 81, p. S37.

Sowerby, J. R., and Keppler, H., 2000, Supercritical behaviour in pegmatites: Direct observation in the hydrothermal diamond anvil cell. American Geophysical Union Transactions, v. 81, p. S37.

Wu, T.C., Shen, A.H., Weathers, M.S., Bassett, W.A., and Chou, I.M., 1995, Anisotropic thermal expansion of calcite at high pressures: An in-situ X-ray diffraction study in a hydrothermal diamond-anvil cell: American Mineralogist, v. 80, P. 941-946.

Groos, G.F., 1997, Montmorillonite under high H₂O pressure: stability of hydrate phases, rehydration hysteresis, and the effect of interlayer cations. American Mineralogist, v. 82, p. 69-78.