Quench Rate Profiles in Water, Air and Liquid Nitrogen

Zhengjiu Xu (zhengjiu@umich.edu) & Youxue Zhang (youxue@umich.edu)

Dept. of Geol. Sci., Univ. of Michigan, Ann Arbor, MI 48109-1063, USA

When red hot lava enters water, what is the cooling rate? We investigated this problem using the hydrous species geospeedometer developed in this laboratory [1]. For a chunk of lava dropped in water, within 0.4 mm of the surface, the quench rates are high enough to preserve the species concentrations at the experimental temperature. Further away, quench rates are slower and can be quantified to be 300°C/s at 0.7 mm from the quench surface to 65°C/s at 3.3 mm. We also determined quench rates for a lava cooled in air and in liquid nitrogen using the same technique to be 12°C/s and 18°C/s, respectively. This order of quenching efficiency is consistent with the results of Dyar and Birnie [2]. When the experimentally determined quench rates are compared with calculations in literature [3], the agreement is good for water cooling, but poor for liquid nitrogen and air cooling. The rough agreement for water cooling is because water is an effective quenching agent and the details of heat transfer in water is not very important. For liquid nitrogen and air quench, however, the details of heat transfer in liquid nitrogen and air plays a determining role. Hence calculation using empirical heat transfer coefficients is not accurate enough. More detailed physical cooling model must be constructed to account for the cooling in such medium.

Zhang Y, Jenkins J & Xu Z, GCA, 61, 2167-2173, (1997).

Dyar MD & Birnie DP, J. Non-Cryst. Solids, 67, 397-412, (1984).

Birnie D.& Dyar MD, JGR, 91, D509-D513, (1986).

Wolframite Solubility in Chloride and Fluoride Solutions at 300 to 600°C and 100 MPa

George P. Zaraisky (zaraisky@iem.ac.ru)

Institute of Experimental, Mineralogy, Russian AS, Chernogolovka, 142432, Russia

The solubility of natural wolframite (44.1 mol.% Frb) has been studied at 100 MPa (± 0.05 Mpa), T=300-600°C (± 5°C) in the NaCl, HCl and HF aqueous solutions of concentration from 0.03 to 10 mole/kg H₂O. The experiments were run in autoclaves in "floating" sealed gold containers of 23 cm³. Run duration were from 2 to 6 weeks. The solubility was determined by the weight loss af a single crystal (measured accurately to 0.2 mg) and by the chemical analysis. The solubility was nearly congruent over the entire concentration range of the NaCl solutions (0.03-8.0 m) and in the 0.1 m HF solution. At the HF concentration from 0.1 m to 10.0 m the solution is enriched in Fe and Mn with respect to W. In the 0.1-10.0 m HCl solutions wolframite undergoes distinctly incongruent dissolution accompanied by heavy losses of Fe and Mn (to 0.1-1.0 m) and the formation of a leached layer of fine fibrous indigo-blue tungsten compound on the crystal surface. The experiments show positive temperature dependence of wolframite solubility in NaCl, HCl and HF solutions. For 1 m NaCl solution, m (sum) W in the solution varies from 0.0002 m at 300°C to 0.007 m at 600°C. In 0.1 m HCl and HF solutions, the (sum) W values are 0.00005 and 0.003 m at the same temperatures. The concentration dependence of W passing into solution is also positive. In the region of NaCl, HCl and HF concentrations from 0.01 to 1.0 m, the slope of the solubility curves is about the same for all the three solutions. The m (sum) W values are here in the range 0.0001 m to 0.001 m. At NaCl and HF concentrations greater than 4 m and 0.5 m, respectively, the solubility of wolframite increases greatly, suggesting that new W-complexes might have formed in this region. The break of the concentration curve in runs using NaCl may be due to the formation of a Na-bearing complex of W, such as NaHWO₄, as proposed by Wood and Vlassopoulos (1989). By analogy with Al and Si complexing in HF aqueous solutions (Zaraisky and Soboleva, 1997), it is likely that similar tungsten hydroxyfluoride complexes of the type W(OH)_nF_6-n may exist in these solutions.

Wood SA & Vlassopoulos D, Geochim. Cosmoshim Acta, 53, 303-312, (1989).

Zaraisky GP & Soboleva YuB, Proc. 5-th Intern. Symp. on Hydrothermal Reactions. Palmer DA & Wesolowski DJ eds. Gatlinburg, USA, 201-205, (1997).

Oxygen Diffusion in the Orthopyroxene Solid Solution: A TG Study

Michele Zema (michele@elicona.unipv.it)¹, Paolo Ghigna (paolo@chifis.unipv.it)², M. Chiara Domeneghetti (domeneghetti@crystal.unipv.it)³ & Vittorio Tazzoli (tazzoli@crystal.unipv.it)³

¹ Centro Grandi Strumenti - Università di Pavia, Via Bassi 21, 27100 Pavia, Italy

² Dipartimento di Chimica Fisica - Università di Pavia, V.le Taramelli 16, 27100 Pavia, Italy

³ Dipartimento di Scienze della Terra - Università di Pavia, Via Ferrata 1, 27100 Pavia, Italy

Oxygen partial pressure is supposed, by analogy with olivines, to influence the kinetics of the Fe-Mg exchange reaction in orthopyroxene. It has been demonstrated for olivines that the Fe-Mg interdiffusion coefficient is dependent on P(O₂), according to D_Fe-Mg (alpha) P(O₂)^~1/6 (Buening and Buseck, 1973; Nakamura and Schmalzried, 1983, 1984). Thermogravimetric analyses were performed on orthopyroxene from the volcanic rock L3 (Aeolian Islands, Italy) under two different P(O₂) conditions, an "O₂-rich" atmosphere (10^-6 atm) and an "O₂-poor" atmosphere (5x10^-19 atm, obtained using a mixture of Fe and FeO heated at 700°C). In both cases ~35 mg of orthopyroxene grains (granulometry 125-250µm) were heated at 400, 500 and 600°C. The opposite trends observed in the two TG plots (an increase in weight in the "O₂-rich" atmosphere and a sharp loss of weight in the "O₂-poor" atmosphere) indicate that oxygen moves into or out of the orthopyroxene lattice in response to an oxygen chemical potential gradient and hence orthopyroxene stoichiometry varies as a function of P(O₂). Therefore, in orthopyroxene, as well as in olivine, the Fe/Mg interdiffusion and hence the kinetics of the Fe-Mg intracrystalline exchange should be affected by P(O₂). In order to determine the time required by the orthopyroxene lattice to equilibrate with the atmosphere at the experimental conditions normally used for single-crystal annealing studies, a TG experiment was performed on the orthopyroxene from the TPK-30F granulite. The sample was heated to 750°C at a rate of ~50°C/min. The TG plot showed that the sample started losing weight at ~250°C and reached equilibrium in less than ten minutes when temperature had not yet stabilized. No more loss of weight was observed during the isotherm. This is evidence that in these operating conditions the orthopyroxene is always at equilibrium with the atmosphere.

Buening DK, Buseck PR, J.Geophys.Res, 78, 6852-6861, (1973).

Nakamura A, Schmalzried H, Phys.Chem.Minerals, 10, 27-37, (1983).

Nakamura A, Schmalzried H, Ber. Bunsenges. Phys. Chem, 88, 140-145, (1984).