The Retrogression of Ultramafic Granulites from the Scourian of NW Scotland

Jane D. Sills
Geology Department, University of Leicester, Leicester, LE1 7RH

Abstract: Scourian ultramafic granulites from the Assynt region, of Sutherland were retrogressed to amphibolite facies during the Inverian and in Laxfordian shear zones. Inverian assemblages are dominantly chlorite and tremolite with minor anthophyllite and dolomite. Laxfordian assemblages are cummingtonite, chlorite, and dolomite with only minor amounts of tremolite. Retrogression took place on a falling temperature path with temperatures between 750 and 550°C, and with H2O forming more than 90% of the fluid phase. Initially retrogression was caused by the influx of large volumes of hydrous fluid associated with the development of Inverian folds. During the Laxfordian shearing PCO2 was increased slightly. Serpentinization of olivine occurred at a much later stage.

Mineralogical Magazine; March 1982 v. 46; no. 338; p. 55-61; DOI: 10.1180/minmag.1982.046.338.10
© 1982, The Mineralogical Society
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