NDLI: Dehydration of dioctahedral aluminous phyllosilicates: thermodynamic modelling and implications for thermobarometric estimates

Content Provider	Springer Nature Link
Author	Dubacq, Beît Vidal, Olivier Andrade, Vincent
Copyright Year	2009
Abstract	We propose a solid-solution model for dioctahedral aluminous phyllosilicates accounting for the main compositional variations, including hydration, observed in natural smectites, interlayered illite/smectite, illites, and phengites from diagenetic to high-grade metamorphic conditions. The suggested formalism involves dehydrated micas and hydrated pyrophyllite-like thermodynamic end-members. With these end-members, the equilibrium conditions of quartz + water + K-bearing mica-like phyllosilicates of fixed 2:1 composition are represented by a line in P–T space along which the interlayer water content varies. The relevant thermodynamic properties required for the calculation of equilibrium conditions were derived using a set of 250 natural data of known maximal temperature and pressure conditions, which covers a range between 25°C and few MPa to 800°C and 5 GPa. The temperatures calculated at fixed pressure with our model are in fair agreement with those reported in the literature for the 250 natural data. At low temperature and pressure, the amount of interlayer water in K-deficient phengite and illite is predicted to reach 100% of the apparent vacancies, which is consistent with previous values reported in the literature. Although the amount of interlayer water is predicted to decrease with pressure and temperature, it is calculated to be significant in K-deficient phengite from LT–HP pelites metamorphosed at about 350°C, 10 kbar. The presence of molecular water in the interlayer site of such phengites has been confirmed by FTIR mapping. Its implications for P–T estimates are discussed.
Starting Page	159
Ending Page	174
Page Count	16
File Format	PDF
ISSN	00107999
Journal	Contributions to Mineralogy and Petrology
Volume Number	159
Issue Number	2
e-ISSN	14320967
Language	English
Publisher	Springer-Verlag
Publisher Date	2009-07-24
Publisher Place	Berlin/Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Thermodynamics Clay minerals Hydration Thermobarometry Phengites Solid solution Mineralogy Mineral Resources Geology
Content Type	Text
Resource Type	Article
Subject	Geochemistry and Petrology Geophysics

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