ISSN:
1432-0967
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract Recent experimental, theoretical, and thermodynamic studies permit better calibration of two reactions for geobarometry: grossular+pyrope+quartz=anorthite+enstatite grossular+almandine+quartz=anorthite+ferrosilite If both reactions are applied using the same thermodynamic data and activity models they should yield the same pressure for a given garnet-pyroxene-plagioclase-quartz assemblage. Application to a variety of high-grade terrains generally yielded excellent results. However, poor results have been obtained for high-Fe rocks which can be traced to errors in activity models for garnet and/or pyroxene. Either a two-site ideal mixing model for orthopyroxene (cf. Wood and Banno 1973) underestimates enstatite activity for high-Fe orthopyroxenes or the Ganguly and Saxena (1984) model overestimates pyrope activity in low-Mg garnets. Application of both barometers to a variety of high-grade terrains gives the following average pressures: Terrain Mg-reaction Fe-reaction Adirondacks, New York 11.2 8.0 Buksefjorden, Greenland 9.5 8.89 Doubtful Sound, New Zealand 12.6 12.0 Enlish River subprovince, Ontario 4.7 5.4 Furua Complex, Tanzania 10.8 10.6 Granite Falls, Minnesota 5.3 6.9 Huntley-Portsoy, Scotland 3.8 4.1 Inarijärvi Complex, Finland 6.0 6.7 Indian Shield 8.9 9.5 Kapuskasing Zone, Ontario 7.8 8.2 Lachnagar, Scotland 3.9 2.6 Molodezhnaya Station, Antartica 7.1 7.5 Nain Province, Labrador 3.6 1.6 Otter Lake, Quebec 9.3 7.7 Qianxi Country, China 11.0 10.7 The above pressures are, in general, in excellent agreement with previous estimates. The results for the English River subprovince and for the Minnesota River Valley further support the idea that the Archean crust was, in some areas, in excess of 20 km thick.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01177592
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