Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

Journal of the Geological Society

This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Thompson, A. B. Search for Related Content GeoRef GeoRef Citation

Fluid-absent metamorphism

Many interpretations of metamorphic parageneses tacitly assume that a free fluid phase was always present during metamorphic equilibration (fluid-present metamorphism), as opposed to the circumstance that, while volatile species are certainly released from minerals during metamorphism, these species may not saturate the grain boundaries to produce free fluid (fluid-absent metamorphism). H₂O-activity has meaning for both fluid-present and fluid-absent metamorphism and may be evaluated if an equilibrium may be written involving H₂O and the temperature and rock-pressure of equilibration are known. P_H2O has only a physical meaning for fluid-present metamorphism.

Although the effects of an aqueous fluid on displacing reactions in P–T space are well known, as are the enhanced kinetic and deformational effects of excess fluid, there is actually little compelling evidence to suggest that the presence of aqueous fluids is common during metamorphism of the middle and lower crust, and the mantle, for the duration of most dynamic processes, including partial melting. Possible exceptions are discontinuous dehydration reactions which affect large compositional ranges of metamorphic rock over narrow pressure–temperature intervals and which could locally produce a free liquid if production rate exceeds escape rate.

Evidence from stable isotopes and fluid inclusions obviously points to the accumulation of free aqueous fluid in definite locations for limited duration, but cannot, unfortunately, be used as evidence for generalized fluid transport during regional or contact metamorphism. Both mineralogical and textural criteria presently used to infer ubiquitous fluid, must be examined in terms of crustal volume and duration of dynamic processes to deduce the presence or absence of free fluid. If volatile components ever saturate grain boundaries, then the fluid-phase may only exist locally and perhaps only for short periods of time. Flow of metamorphic fluid may be focused into narrow regimes that could be quite widely spaced. Fluid-present metamorphism should not be considered as typical of whole crust evolution.

This article has been cited by other articles:

				G. Phillips, D. E. Kelsey, A. F. Corvino, and R. A. Dutch Continental Reworking during Overprinting Orogenic Events, Southern Prince Charles Mountains, East Antarctica J. Petrology, November 1, 2009; 50(11): 2017 - 2041. [Abstract] [Full Text] [PDF]

				E. F. Baxter Natural constraints on metamorphic reaction rates Geological Society, London, Special Publications, January 1, 2003; 220(1): 183 - 202. [Abstract] [PDF]

				J. Konzett and P. Ulmer The Stability of Hydrous Potassic Phases in Lherzolitic Mantle--an Experimental Study to 9.5 GPa in Simplified and Natural Bulk Compositions J. Petrology, April 1, 1999; 40(4): 629 - 652. [Abstract] [Full Text] [PDF]

				A. B. THOMPSON Some aspects of fluid motion during metamorphism Journal of the Geological Society, April 1, 1987; 144(2): 309 - 312. [Abstract] [PDF]

				A. C. BARNICOAT and N. FRY High-pressure metamorphism of the Zermatt-Saas ophiolite zone, Switzerland Journal of the Geological Society, July 1, 1986; 143(4): 607 - 618. [Abstract] [PDF]