H2O activity in albite melts at deep crustal P-T conditions derived from melting experiments in the systems NaAlSi3O8-H2O-CO2 and NaAlSi3O8-H2O-NaCl
- Authors: Makhluf A.R.1, Newton R.C.1, Manning C.E.1
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Affiliations:
- Department of Earth, Planetary and Space Sciences
- Issue: Vol 25, No 5 (2017)
- Pages: 449-457
- Section: Article
- URL: https://journals.rcsi.science/0869-5911/article/view/177535
- DOI: https://doi.org/10.1134/S0869591117050046
- ID: 177535
Cite item
Abstract
The system NaAlSi3O8 (albite, Ab)-H2O offers a simple and tractable model to study the thermodynamics of the volatile constituent H2O in felsic magmas. Although it has been studied in this context for nearly 100 years, developing a comprehensive model that adequately describes the activity of H2O (\({a_{{H_2}O}}\)) in hydrous albite liquids and vapors has proven challenging. There are several problems. First, \({a_{{H_2}O}}\) in hydrous liquids relies on melting experiments in the presence of mixed fluids with reduced H2O activity (H2O-CO2 and H2O-NaCl), but models of \({a_{{H_2}O}}\) in these coexisting fluids have lacked sufficient accuracy. Second, the role of the solubility of albite in H2O has been assumed to be negligible; however, it is important to take solubility into account at pressure (P) above 0.5 GPa because it becomes sufficiently high that H2O activity at the wet solidus is significantly less than 1. Third, the dry melting temperatures and wet solidus temperatures are inconsistent between the datasets. We address these issues by combining previous experimental work on T–\({X_{{H_2}O}}\) liquidus relations at 0.5–1.5 GPa with accurate activity formulations for H2O in mixed fluids (Aranovich and Newton, 1996, 1999). This yields isobaric T–\({a_{{H_2}O}}\) sections at 0.5, 0.7, 1.0 and 1.5 GPa. Data at each isobar were fit to cubic equations, which were used to derive the following equation for liquidus T as a function of \({a_{{H_2}O}}\) and P:
About the authors
A. R. Makhluf
Department of Earth, Planetary and Space Sciences
Author for correspondence.
Email: amakhluf@epss.ucla.edu
United States, Los Angeles, CA, 90095
R. C. Newton
Department of Earth, Planetary and Space Sciences
Email: amakhluf@epss.ucla.edu
United States, Los Angeles, CA, 90095
C. E. Manning
Department of Earth, Planetary and Space Sciences
Email: amakhluf@epss.ucla.edu
United States, Los Angeles, CA, 90095
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