US EPA

7462051 

Journal Article 

The role of alkalis in the formation of coronitic textures in metamangerites and metaanorthosites from the Adirondack Complex, United States (vol 6, pg 583, 1998) 

Safonov, OG 

1999 

1 

Petrology
ISSN: 0869-5911
EISSN: 1531-8540 

7 

1 

102-121 

English 

WOS:000078723500007 

The effect of potassium and sodium activities on corona-forming reactions during the retrograde stage of metamorphism is studied and exemplified by metamangerites and metaanorthosites from the Adirondack Complex, New York State, United States. K-feldspar rims and veinlets, which accompany garnet and amphibole coronitic textures in the orthorocks, are the mineralogic indicators of rock interaction with fluids containing potassium and sodium salts. The calcium content of garnet in the rocks systematically increases from the earliest generation of the mineral to the latest, which coexist with newly formed K-feldspar. According to the reaction CaAl2Si2O8 + 3SiO2 + {4/3K+ + 2/3H2O} = 4/3KAlSi3O8 + 1/3Ca3Al2Si3O12 + 4/3H+ An Qtz fluid Kfs Grs fluid an increase in the calcium content of the garnet corresponds to an increase in the alkali activity in the fluid (at constant T and P) during corona growth. Calculation of temperature, pressure, oxygen, and alkali activities showed that the formation of garnet-K-feldspar-quartz coronas in metamangerites and metaanorthosites from the Adirondack Complex has taken place at T = 700-600°C, P = 7-6 kbar under conditions of low oxygen and carbon dioxide activities and has resulted from the isobaric cooling of the rocks from metamorphic peak at high potassium and sodium activities in aqueous-chloride reduced fluid. The determining factor in the formation of the Grt + Kfs + Qtz assemblage of the rocks was low aH2Ofl, which was caused by the high concentration of potassium and sodium salts (up to Xsalts = 0.7) in the fluid. Two consequent stages were distinguished in the evolution of fluid in the Adirondack Complex: (1) high-temperature (700-600°C) stage of rock interaction with aqueous fluid saturated with potassium and sodium chlorides and (2) low-temperature (<600°C) stage of rock alteration by aqueous-carbon dioxide fluids. Copyright © 1998 by MAEe cyrillic signK "Hayκa/Interperiodica". 

Physical Sciences - Other Topics; transport-properties, fluid inclusions, isotope evidence,; high-pressures, new-york, granulites, metamorphism, equilibria,; amphiboles, garnet