HR: 1330h
AN: V22D-0613    [PDF]
TI: Solubility of Albite + Paragonite $\pm$ Quartz in H$_{2}$O at 1 GPa, $580\deg$C: Implications for Metamorphic Fluids
AU: * Antignano, A
EM: aaiv@ess.ucla.edu
AF: Dept. of Earth and Space Sciences, University of Calfornia, Los Angeles, CA 90095
AU: Manning, C
EM: manning@ess.ucla.edu
AF: Dept. of Earth and Space Sciences, University of Calfornia, Los Angeles, CA 90095
AB: One of the most common mineral assemblages in crustal metamorphism is feldspar + quartz; however, little is known about the solubility of this assemblage in metamorphic fluids. We measured the solubility of albite and albite+quartz in H$_{2}$O at $580\deg$C and 1.0 GPa using a piston cylinder apparatus. Experiments were conducted using Amelia albite in NaCl-graphite assemblies. Experiments were conducted using a double capsule arrangement. Inner capsules consisting of perforated 1.6 mm OD Pt capsules containing a single albite crystal were load in 3.5mm OD outer capsules containing ultra pure H$_{2}$O $\pm$ quartz. Solubility was determined by the weight loss of single albite and quartz grains after 8 hr runs. Time series experiments on this system show no variation in fluid composition or solubility after 4hrs. Albite exhibited incongruent dissolution, yielding paragonite as a husk that mantles the albite grain. The composition of the fluid was determined by mass balance as determined by the weights of albite, quartz, and paragonite. In the albite-only experiments, the concentration of total dissolved solids (TDS) were 0.628 molal, with Na, Al and Si in the fluid of 0.137, 0.081, and 0.41 molal, respectively, and Na/Al of 1.691. In the presence of quartz, there is an increase in the overall TDS to 0.777 molal. Albite-quartz experiments produce an increase in Si concentration to 0.628 molal, with lower Na and Al concentrations of 0.098 and 0.051 molal, respectively, and Na/Al of 1.922. The aqueous Si concentrations in the albite-only experiments are higher than those in fluid equilibrated with quartz (Manning, 1994, GCA, 58, 4831) at the same conditions. This is consistent with the data of Anderson and Burnham (1983, Am. J. Sci., 283-A, 283) on albite. In the quartz-present experiments results show still higher Si concentration in the fluid phase. Our results demonstrate enhanced solubility of silica in the presence of albite and albite+quartz, relative to quartz alone, suggesting that the additional components promote complexing, perhaps through polymerization. This solubility enhancement has implications for the nature of transport in deep crustal pelitic systems, allowing for a greater abundance of silica to be removed by a fluid phase during metamorphism. The enhancement of silica solubility indicates that models of simple, aqueous metamorphic fluids must account for silica polymerization, and that such fluids may carry a substantially greater solute load than has previously been recognized.
DE: 3630 Experimental mineralogy and petrology
DE: 3640 Igneous petrology
DE: 3660 Metamorphic petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting