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6911068 
Journal Article 
Petrologic evidence for K-feldspar metasomatism in granulite facies rocks 
Harlov, DE; Hansen, EC; Bigler, C; , 
1998 
Yes 
Chemical Geology
ISSN: 0009-2541 
ELSEVIER SCIENCE BV 
AMSTERDAM 
151 
1-4 
373-386 
English 
WOS:000076718300026 
We present evidence for K-feldspar metasomatism in chamockitic granulites from two well-known terranes: the Shevaroy Hills Massif, S. India (750 degrees C, 8 kbars) and the Bamble Sector, S.E. Norway (790 degrees C, 7.5 kbars) in the form of K-feldspar veins principally along plagioclase and quartz grain boundaries and in the form of highly variable antiperthitic patches of K-feldspar in an uneven scattering of plagioclase grains. With one exception, orthopyroxene or amphibole grains in contact with these K-feldspar veins show no alteration to secondary biotite, indicating that the H(2)O activity of the fluids responsible for these veins must have been relatively low. A high Ba concentration in these veins also suggests a metasomatic origin. Point counted, back-scattered electron photomicrographs, along with microprobe analyses, provide reintegrated K-feldspar and plagioclase compositions for 8 to 12 predetermined random areas per thin section for three samples from Bamble and three samples from the Shevaroy Hills. These reintegrated feldspar compositions plot over a range of temperatures on the feldspar ternary for each sample, and indicate saturation temperatures above the mean temperature for either region with a few reintegrated compositions above the 1000 degrees C isotherm and with the lower cut-off temperatures at 700 degrees C and 600 degrees C for the Shevaroy and Bamble samples, respectively. These patterns suggest that exsolution alone could not have been responsible for the formation of the K-feldspar veins and patches in these rocks. We suggest that these veins are due to the influx of complex, supercritical, low H(2)O activity brines shortly after peak metamorphic conditions, that this influx continued during the initial phases of post-peak metamorphic uplift and that these fluids represent the first stage in a series of fluid influxes in which the H(2)O activity increased as uplift continued. Reaction of these brines with potassium-undersaturated plagioclase grains formed K-feldspar veins along grain boundaries and fractures, as well as diffusing into the plagioclase, which became supersaturated, and exsolved K-feldspar as antiperthite patches during uplift and cooling. Formation of secondary biotite halos around orthopyroxene in one sample associated with these K-feldspar veins can be explained by heightened H(2)O activity in the brines due to enrichment in H(2)O, emplacement of the veins at lower pressure during uplift or both compared to the other Shevaroy and Bamble samples. (C) 1998 Elsevier Science B.V. All rights reserved. 
NaCl-KCl brines; K-feldspar metasomatism; replacement antiperthite; granulites; charnockites 
European Research Conference on the Geochemistry of Crustal Fluids 
SEEFELD, AUSTRIA