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7466667 
Journal Article 
FLUID INFILTRATION AND REGIONAL METAMORPHISM OF THE WAITS RIVER FORMATION, NORTH-EAST VERMONT, USA 
Leger, A; Ferry, JM 
1993 
Yes 
Journal of Metamorphic Geology
ISSN: 0263-4929
EISSN: 1525-1314 
BLACKWELL SCIENCE INC 
CAMBRIDGE 
11 
1 
3-29 
WOS:A1993KF36900001 
The Siluro-Devonian Waits River Formation of north-east Vermont was deformed, intruded by plutons and regionally metamorphosed during the Devonian Acadian Orogeny. Five metamorphic zones were mapped based on the mineralogy of carbonate rocks. From low to high grade, these are: (1) ankerite-albite, (2) ankerite-oligoclase, (3) biotite, (4) amphibole and (5) diopside zones. Pressure was near 4.5 kbar and temperature varied from c. 450-degrees-C in the ankerite-albite zone to c. 525-degrees-C in the diopside zone. Fluid composition for all metamorphic zones was estimated from mineral equilibria. Average calculated X(CO2)[= CO2/(CO2 + H2O)] of fluid in equilibrium with the marls increases with increasing grade from 0.05 in the ankerite-oligoclase zone. to 0.25 in the biotite zone and to 0.44 in the amphibole zone. In the diopside zone, X(CO2) decreases to 0.06.Model prograde metamorphic reactions were derived from measured modes, mineral chemistry, and whole-rock chemistry. Prograde reactions involved decarbonation with an evolved volatile mixture of X(CO2) > 0.50. The X(CO2) of fluid in equilibrium with rocks from all zones, however, was generally <0.40. This difference attests to the infiltration of a reactive H2O-rich fluid during metamorphism. Metamorphosed carbonate rocks from the formation suggests that both heat flow and pervasive infiltration of a reactive H2O-rich fluid drove mineral reactions during metamorphism. Average time-integrated volume fluxes (cm3 fluid/cm2 rock), calculated from the standard equation for coupled fluid flow and reaction in porous media, are ( 1) ankerite-oligoclase zone: c. 1 X 10(4); (2) biotite zone: c. 3 x 10(4); (3) amphibole zone: c. 10 X 10(4); and diopside zone: c. 60 X 10(4). The increase in calculated flux with increasing grade is at least in part the result of internal production of volatiles from prograde reactions in pelitic schists and metacarbonate rocks within the Waits River Formation.The mapped pattern of time-integrated fluxes indicates that the Strafford-Willoughby Arch and the numerous igneous intrusions in the field area focused fluid flow during metamorphism. Many rock specimens in the diopside zone experienced extreme alkali depletion and also record low X(CO2). Metamorphic fluids in equilibrium with diopside zone rocks may therefore represent a mixture of acid, H2O-rich fluids given off by the crystallizing magmas, and CO2-H2O fluids produced by devolatilization reactions in the host marls. Higher fluxes and different fluid compositions recorded near the plutons suggest that pluton-driven hydrothermal cells were local highs in the larger regional metamorphic hydrothermal system 
METAMORPHIC FLUID INFILTRATION; REGIONAL AND PLUTON-DRIVEN HYDROTHERMAL SYSTEMS; TIME-INTEGRATED FLUID FLUXES